Publications by authors named "Markku Kulmala"

148 Publications

Indoor Model Simulation for COVID-19 Transport and Exposure.

Int J Environ Res Public Health 2021 03 12;18(6). Epub 2021 Mar 12.

Institute for Atmospheric and Earth System Research (INAR/Physics), University of Helsinki, FI-00014 Helsinki, Finland.

Transmission of respiratory viruses is a complex process involving emission, deposition in the airways, and infection. Inhalation is often the most relevant transmission mode in indoor environments. For severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the risk of inhalation transmission is not yet fully understood. Here, we used an indoor aerosol model combined with a regional inhaled deposited dose model to examine the indoor transport of aerosols from an infected person with novel coronavirus disease (COVID-19) to a susceptible person and assess the potential inhaled dose rate of particles. Two scenarios with different ventilation rates were compared, as well as adult female versus male recipients. Assuming a source strength of 10 viruses/s, in a tightly closed room with poor ventilation (0.5 h), the respiratory tract deposited dose rate was 140-350 and 100-260 inhaled viruses/hour for males and females; respectively. With ventilation at 3 h the dose rate was only 30-90 viruses/hour. Correcting for the half-life of SARS-CoV-2 in air, these numbers are reduced by a factor of 1.2-2.2 for poorly ventilated rooms and 1.1-1.4 for well-ventilated rooms. Combined with future determinations of virus emission rates, the size distribution of aerosols containing the virus, and the infectious dose, these results could play an important role in understanding the full picture of potential inhalation transmission in indoor environments.
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http://dx.doi.org/10.3390/ijerph18062927DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7999367PMC
March 2021

Rapid conversion of isoprene photooxidation products in terrestrial plants.

Commun Earth Environ 2020 4;1:44. Epub 2020 Nov 4.

Department of Ion Physics and Applied Physics, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria.

Isoprene is emitted from the biosphere into the atmosphere, and may strengthen the defense mechanisms of plants against oxidative and thermal stress. Once in the atmosphere, isoprene is rapidly oxidized, either to isoprene-hydroxy-hydroperoxides (ISOPOOH) at low levels of nitrogen oxides, or to methyl vinyl ketone (MVK) and methacrolein at high levels. Here we combine uptake rates and deposition velocities that we obtained in laboratory experiments with observations in natural forests to show that 1,2-ISOPOOH deposits rapidly into poplar leaves. There, it is converted first to cytotoxic MVK and then most probably through alkenal/ one oxidoreductase (AOR) to less toxic methyl ethyl ketone (MEK). This detoxification process is potentially significant globally because AOR enzymes are ubiquitous in terrestrial plants. Our simulations with a global chemistry-transport model suggest that around 6.5 Tg yr of MEK are re-emitted to the atmosphere. This is the single largest MEK source presently known, and recycles 1.5% of the original isoprene flux. Eddy covariance flux measurements of isoprene and MEK over different forest ecosystems confirm that MEK emissions can reach 1-2% those of isoprene. We suggest that detoxification processes in plants are one of the most important sources of oxidized volatile organic compounds in the atmosphere.
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http://dx.doi.org/10.1038/s43247-020-00041-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7894407PMC
November 2020

Role of iodine oxoacids in atmospheric aerosol nucleation.

Authors:
Xu-Cheng He Yee Jun Tham Lubna Dada Mingyi Wang Henning Finkenzeller Dominik Stolzenburg Siddharth Iyer Mario Simon Andreas Kürten Jiali Shen Birte Rörup Matti Rissanen Siegfried Schobesberger Rima Baalbaki Dongyu S Wang Theodore K Koenig Tuija Jokinen Nina Sarnela Lisa J Beck João Almeida Stavros Amanatidis António Amorim Farnoush Ataei Andrea Baccarini Barbara Bertozzi Federico Bianchi Sophia Brilke Lucía Caudillo Dexian Chen Randall Chiu Biwu Chu António Dias Aijun Ding Josef Dommen Jonathan Duplissy Imad El Haddad Loïc Gonzalez Carracedo Manuel Granzin Armin Hansel Martin Heinritzi Victoria Hofbauer Heikki Junninen Juha Kangasluoma Deniz Kemppainen Changhyuk Kim Weimeng Kong Jordan E Krechmer Aleksander Kvashin Totti Laitinen Houssni Lamkaddam Chuan Ping Lee Katrianne Lehtipalo Markus Leiminger Zijun Li Vladimir Makhmutov Hanna E Manninen Guillaume Marie Ruby Marten Serge Mathot Roy L Mauldin Bernhard Mentler Ottmar Möhler Tatjana Müller Wei Nie Antti Onnela Tuukka Petäjä Joschka Pfeifer Maxim Philippov Ananth Ranjithkumar Alfonso Saiz-Lopez Imre Salma Wiebke Scholz Simone Schuchmann Benjamin Schulze Gerhard Steiner Yuri Stozhkov Christian Tauber António Tomé Roseline C Thakur Olli Väisänen Miguel Vazquez-Pufleau Andrea C Wagner Yonghong Wang Stefan K Weber Paul M Winkler Yusheng Wu Mao Xiao Chao Yan Qing Ye Arttu Ylisirniö Marcel Zauner-Wieczorek Qiaozhi Zha Putian Zhou Richard C Flagan Joachim Curtius Urs Baltensperger Markku Kulmala Veli-Matti Kerminen Theo Kurtén Neil M Donahue Rainer Volkamer Jasper Kirkby Douglas R Worsnop Mikko Sipilä

Science 2021 02 4;371(6529):589-595. Epub 2021 Feb 4.

Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, 00014 Helsinki, Finland.

Iodic acid (HIO) is known to form aerosol particles in coastal marine regions, but predicted nucleation and growth rates are lacking. Using the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber, we find that the nucleation rates of HIO particles are rapid, even exceeding sulfuric acid-ammonia rates under similar conditions. We also find that ion-induced nucleation involves IO and the sequential addition of HIO and that it proceeds at the kinetic limit below +10°C. In contrast, neutral nucleation involves the repeated sequential addition of iodous acid (HIO) followed by HIO, showing that HIO plays a key stabilizing role. Freshly formed particles are composed almost entirely of HIO, which drives rapid particle growth at the kinetic limit. Our measurements indicate that iodine oxoacid particle formation can compete with sulfuric acid in pristine regions of the atmosphere.
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http://dx.doi.org/10.1126/science.abe0298DOI Listing
February 2021

Direct field evidence of autocatalytic iodine release from atmospheric aerosol.

Proc Natl Acad Sci U S A 2021 Jan;118(4)

Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, 00014 Helsinki, Finland;

Reactive iodine plays a key role in determining the oxidation capacity, or cleansing capacity, of the atmosphere in addition to being implicated in the formation of new particles in the marine boundary layer. The postulation that heterogeneous cycling of reactive iodine on aerosols may significantly influence the lifetime of ozone in the troposphere not only remains poorly understood but also heretofore has never been observed or quantified in the field. Here, we report direct ambient observations of hypoiodous acid (HOI) and heterogeneous recycling of interhalogen product species (i.e., iodine monochloride [ICl] and iodine monobromide [IBr]) in a midlatitude coastal environment. Significant levels of ICl and IBr with mean daily maxima of 4.3 and 3.0 parts per trillion by volume (1-min average), respectively, have been observed throughout the campaign. We show that the heterogeneous reaction of HOI on marine aerosol and subsequent production of iodine interhalogens are much faster than previously thought. These results indicate that the fast formation of iodine interhalogens, together with their rapid photolysis, results in more efficient recycling of atomic iodine than currently considered in models. Photolysis of the observed ICl and IBr leads to a 32% increase in the daytime average of atomic iodine production rate, thereby enhancing the average daytime iodine-catalyzed ozone loss rate by 10 to 20%. Our findings provide direct field evidence that the autocatalytic mechanism of iodine release from marine aerosol is important in the atmosphere and can have significant impacts on atmospheric oxidation capacity.
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http://dx.doi.org/10.1073/pnas.2009951118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7848547PMC
January 2021

Assessing Human Exposure to SVOCs in Materials, Products, and Articles: A Modular Mechanistic Framework.

Environ Sci Technol 2021 01 15;55(1):25-43. Epub 2020 Dec 15.

Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, Virginia 24060, United States.

A critical review of the current state of knowledge of chemical emissions from indoor sources, partitioning among indoor compartments, and the ensuing indoor exposure leads to a proposal for a modular mechanistic framework for predicting human exposure to semivolatile organic compounds (SVOCs). Mechanistically consistent source emission categories include solid, soft, frequent contact, applied, sprayed, and high temperature sources. Environmental compartments are the gas phase, airborne particles, settled dust, indoor surfaces, and clothing. Identified research needs are the development of dynamic emission models for several of the source emission categories and of estimation strategies for critical model parameters. The modular structure of the framework facilitates subsequent inclusion of new knowledge, other chemical classes of indoor pollutants, and additional mechanistic processes relevant to human exposure indoors. The framework may serve as the foundation for developing an open-source community model to better support collaborative research and improve access for application by stakeholders. Combining exposure estimates derived using this framework with toxicity data for different end points and toxicokinetic mechanisms will accelerate chemical risk prioritization, advance effective chemical management decisions, and protect public health.
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http://dx.doi.org/10.1021/acs.est.0c02329DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7877794PMC
January 2021

Is reducing new particle formation a plausible solution to mitigate particulate air pollution in Beijing and other Chinese megacities?

Faraday Discuss 2021 Mar 8;226:334-347. Epub 2020 Dec 8.

Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, China.

Atmospheric gas-to-particle conversion is a crucial or even dominant contributor to haze formation in Chinese megacities in terms of aerosol number, surface area and mass. Based on our comprehensive observations in Beijing during 15 January 2018-31 March 2019, we are able to show that 80-90% of the aerosol mass (PM) was formed via atmospheric reactions during the haze days and over 65% of the number concentration of haze particles resulted from new particle formation (NPF). Furthermore, the haze formation was faster when the subsequent growth of newly formed particles was enhanced. Our findings suggest that in practice almost all present-day haze episodes originate from NPF, mainly since the direct emission of primary particles in Beijing has considerably decreased during recent years. We also show that reducing the subsequent growth rate of freshly formed particles by a factor of 3-5 would delay the buildup of haze episodes by 1-3 days. Actually, this delay would decrease the length of each haze episode, so that the number of annual haze days could be approximately halved. Such improvement in air quality can be achieved with targeted reduction of gas-phase precursors for NPF, mainly dimethyl amine and ammonia, and further reductions of SO emissions. Furthermore, reduction of anthropogenic organic and inorganic precursor emissions would slow down the growth rate of newly-formed particles and consequently reduce the haze formation.
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http://dx.doi.org/10.1039/d0fd00078gDOI Listing
March 2021

Particle growth with photochemical age from new particle formation to haze in the winter of Beijing, China.

Sci Total Environ 2021 Jan 14;753:142207. Epub 2020 Sep 14.

Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, China; Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Finland; Joint International Research Laboratory of Atmospheric and Earth System Sciences, School of Atmospheric Sciences, Nanjing University, Nanjing 210023, China.

Secondary aerosol formation in the aging process of primary emission is the main reason for haze pollution in eastern China. Pollution evolution with photochemical age was studied for the first time at a comprehensive field observation station during winter in Beijing. The photochemical age was used as an estimate of the timescale attributed to the aging process and was estimated from the ratio of toluene to benzene in this study. A low photochemical age indicates a fresh emission. The photochemical age of air masses during new particle formation (NPF) days was lower than that on haze days. In general, the strongest NPF events, along with a peak of the formation rate of 1.5 nm (J) and 3 nm particles (J), were observed when the photochemical age was between 12 and 24 h while rarely took place with photochemical ages less than 12 h. When photochemical age was larger than 48 h, haze occurred and NPF was suppressed. The sources and sinks of nanoparticles had distinct relation with the photochemical age. Our results show that the condensation sink (CS) showed a valley with photochemical ages ranging from 12 to 24 h, while HSO concentration showed no obvious trend with the photochemical age. The high concentrations of precursor vapours within an air mass lead to persistent nucleation with photochemical age ranging from 12 to 48 h in winter. Coincidently, the fast increase of PM mass was also observed during this range of photochemical age. Noteworthy, CS increased with the photochemical age on NPF days only, which is the likely reason for the observation that the PM mass increased faster with photochemical age on NPF days compared with other days. The evolution of particles with the photochemical age provides new insights into understanding how particles originating from NPF transform to haze pollution.
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http://dx.doi.org/10.1016/j.scitotenv.2020.142207DOI Listing
January 2021

Unprecedented Ambient Sulfur Trioxide (SO) Detection: Possible Formation Mechanism and Atmospheric Implications.

Environ Sci Technol Lett 2020 Nov 25;7(11):809-818. Epub 2020 Sep 25.

Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100089, China.

Sulfur trioxide (SO) is a crucial compound for atmospheric sulfuric acid (HSO) formation, acid rain formation, and other atmospheric physicochemical processes. During the daytime, SO is mainly produced from the photo-oxidation of SO by OH radicals. However, the sources of SO during the early morning and night, when OH radicals are scarce, are not fully understood. We report results from two field measurements in urban Beijing during winter and summer 2019, using a nitrate-CI-APi-LTOF (chemical ionization-atmospheric pressure interface-long-time-of-flight) mass spectrometer to detect atmospheric SO and HSO. Our results show the level of SO was higher during the winter than during the summer, with high SO levels observed especially during the early morning (∼05:00 to ∼08:30) and night (∼18:00 to ∼05:00 the next day). On the basis of analysis of SO, NO , black carbon, traffic flow, and atmospheric ions, we suggest SO could be formed from the catalytic oxidation of SO on the surface of traffic-related black carbon. This previously unidentified SO source results in significant HSO formation in the early morning and thus promotes sub-2.5 nm particle formation. These findings will help in understanding urban SO and formulating policies to mitigate secondary particle formation in Chinese megacities.
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http://dx.doi.org/10.1021/acs.estlett.0c00615DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7659313PMC
November 2020

Effects of forests on particle number concentrations in near-road environments across three geographic regions.

Environ Pollut 2020 Nov 1;266(Pt 2):115294. Epub 2020 Aug 1.

University of Helsinki, Ecosystems and Environment Research Programme, Faculty of Biological and Environmental Sciences, Niemenkatu 73, FI, 15140, Lahti, Finland.

Trees and other vegetation have been advocated as a mitigation measure for urban air pollution mainly due to the fact that they passively filter particles from the air. However, mounting evidence suggests that vegetation may also worsen air quality by slowing the dispersion of pollutants and by producing volatile organic compounds that contribute to formation of ozone and other secondary pollutants. We monitored nanoparticle (>10 nm) counts along distance gradients away from major roads along paired transects across open and forested landscapes in Baltimore (USA), Helsinki (Finland) and Shenyang (China) - i.e. sites in three biomes with different pollution levels - using condensation particle counters. Mean particle number concentrations averaged across all sampling sites were clearly reduced (15%) by the presence of forest cover only in Helsinki. For Baltimore and Shenyang, levels showed no significant difference between the open and forested transects at any of the sampling distances. This suggests that nanoparticle deposition on trees is often counterbalanced by other factors, including differing flow fields and aerosol processes under varying meteorological conditions. Similarly, consistent differences in high frequency data patterns between the transects were detected only in Helsinki. No correlations between nanoparticle concentrations and solar radiation or local wind speed as affecting nanoparticle abundances were found, but they were to some extent associated with canopy closure. These data add to the accumulating evidence according to which trees do not necessarily improve air quality in near-road environments.
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http://dx.doi.org/10.1016/j.envpol.2020.115294DOI Listing
November 2020

Seasonal Characteristics of New Particle Formation and Growth in Urban Beijing.

Environ Sci Technol 2020 07 1;54(14):8547-8557. Epub 2020 Jul 1.

State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, 100084 Beijing, China.

Understanding the atmospheric new particle formation (NPF) process within the global range is important for revealing the budget of atmospheric aerosols and their impacts. We investigated the seasonal characteristics of NPF in the urban environment of Beijing. Aerosol size distributions down to ∼1 nm and HSO concentration were measured during 2018-2019. The observed formation rate of 1.5 nm particles () is significantly higher than those in the clean environment, e.g., Hyytiälä, whereas the growth rate is not significantly different. Both and NPF frequency in urban Beijing show a clear seasonal variation with maxima in winter and minima in summer, while the observed growth rates are generally within the same range around the year. We show that ambient temperature is a governing factor driving the seasonal variation of . In contrast, the condensation sink and the daily maximum HSO concentration show no significant seasonal variation during the NPF periods. In all four seasons, condensation of HSO and (HSO)(amine) clusters contributes significantly to the growth rates in the sub-3 nm size range, whereas it is less important for the observed growth rates of particles above 3 nm. Therefore, other species are always needed for the growth of larger particles.
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http://dx.doi.org/10.1021/acs.est.0c00808DOI Listing
July 2020

Photo-oxidation of Aromatic Hydrocarbons Produces Low-Volatility Organic Compounds.

Environ Sci Technol 2020 07 18;54(13):7911-7921. Epub 2020 Jun 18.

Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.

To better understand the role of aromatic hydrocarbons in new-particle formation, we measured the particle-phase abundance and volatility of oxidation products following the reaction of aromatic hydrocarbons with OH radicals. For this we used thermal desorption in an iodide-adduct Time-of-Flight Chemical-Ionization Mass Spectrometer equipped with a Filter Inlet for Gases and AEROsols (FIGAERO-ToF-CIMS). The particle-phase volatility measurements confirm that oxidation products of toluene and naphthalene can contribute to the initial growth of newly formed particles. Toluene-derived (C) oxidation products have a similar volatility distribution to that of α-pinene-derived (C) oxidation products, while naphthalene-derived (C) oxidation products are much less volatile than those from toluene or α-pinene; they are thus stronger contributors to growth. Rapid progression through multiple generations of oxidation is more pronounced in toluene and naphthalene than in α-pinene, resulting in more oxidation but also favoring functional groups with much lower volatility per added oxygen atom, such as hydroxyl and carboxylic groups instead of hydroperoxide groups. Under conditions typical of polluted urban settings, naphthalene may well contribute to nucleation and the growth of the smallest particles, whereas the more abundant alkyl benzenes may overtake naphthalene once the particles have grown beyond the point where the Kelvin effect strongly influences the condensation driving force.
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http://dx.doi.org/10.1021/acs.est.0c02100DOI Listing
July 2020

Rapid growth of new atmospheric particles by nitric acid and ammonia condensation.

Nature 2020 05 13;581(7807):184-189. Epub 2020 May 13.

Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, USA.

A list of authors and their affiliations appears at the end of the paper New-particle formation is a major contributor to urban smog, but how it occurs in cities is often puzzling. If the growth rates of urban particles are similar to those found in cleaner environments (1-10 nanometres per hour), then existing understanding suggests that new urban particles should be rapidly scavenged by the high concentration of pre-existing particles. Here we show, through experiments performed under atmospheric conditions in the CLOUD chamber at CERN, that below about +5 degrees Celsius, nitric acid and ammonia vapours can condense onto freshly nucleated particles as small as a few nanometres in diameter. Moreover, when it is cold enough (below -15 degrees Celsius), nitric acid and ammonia can nucleate directly through an acid-base stabilization mechanism to form ammonium nitrate particles. Given that these vapours are often one thousand times more abundant than sulfuric acid, the resulting particle growth rates can be extremely high, reaching well above 100 nanometres per hour. However, these high growth rates require the gas-particle ammonium nitrate system to be out of equilibrium in order to sustain gas-phase supersaturations. In view of the strong temperature dependence that we measure for the gas-phase supersaturations, we expect such transient conditions to occur in inhomogeneous urban settings, especially in wintertime, driven by vertical mixing and by strong local sources such as traffic. Even though rapid growth from nitric acid and ammonia condensation may last for only a few minutes, it is nonetheless fast enough to shepherd freshly nucleated particles through the smallest size range where they are most vulnerable to scavenging loss, thus greatly increasing their survival probability. We also expect nitric acid and ammonia nucleation and rapid growth to be important in the relatively clean and cold upper free troposphere, where ammonia can be convected from the continental boundary layer and nitric acid is abundant from electrical storms.
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http://dx.doi.org/10.1038/s41586-020-2270-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7334196PMC
May 2020

Responses of gaseous sulfuric acid and particulate sulfate to reduced SO concentration: A perspective from long-term measurements in Beijing.

Sci Total Environ 2020 Jun 5;721:137700. Epub 2020 Mar 5.

State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China; State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Beijing 100084, China. Electronic address:

SO concentration decreased rapidly in recent years in China due to the implementation of strict control policies by the government. Particulate sulfate (pSO) and gaseous HSO (SA) are two major products of SO and they play important roles in the haze formation and new particle formation (NPF), respectively. We examined the change in pSO and SA concentrations in response to reduced SO concentration using long-term measurement data in Beijing. Simulations from the Community Multiscale Air Quality model with a 2-D Volatility Basis Set (CMAQ/2D-VBS) were used for comparison. From 2013 to 2018, SO concentration in Beijing decreased by ~81% (from 9.1 ppb to 1.7 ppb). pSO concentration in submicrometer particles decreased by ~60% from 2012-2013 (monthly average of ~10 μg·m) to 2018-2019 (monthly average of ~4 μg·m). Accordingly, the fraction of pSO in these particles decreased from 20-30% to <10%. Increased sulfur oxidation ratio was observed both in the measurements and the CMAQ/2D-VBS simulations. Despite the reduction in SO concentration, there was no obvious decrease in SA concentration based on data from several measuring periods from 2008 to 2019. This was supported by the increased SA:SO ratio with reduced SO concentration and condensation sink. NPF frequency in Beijing between 2004 and 2019 remains relatively constant. This constant NPF frequency is consistent with the relatively stable SA concentration in Beijing, while different from some other cities where NPF frequency was reported to decrease with decreased SO concentrations.
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http://dx.doi.org/10.1016/j.scitotenv.2020.137700DOI Listing
June 2020

Formation and growth of sub-3-nm aerosol particles in experimental chambers.

Nat Protoc 2020 03 12;15(3):1013-1040. Epub 2020 Feb 12.

Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki, Finland.

Atmospheric new particle formation (NPF), which is observed in many environments globally, is an important source of boundary-layer aerosol particles and cloud condensation nuclei, which affect both the climate and human health. To better understand the mechanisms behind NPF, chamber experiments can be used to simulate this phenomenon under well-controlled conditions. Recent advancements in instrumentation have made it possible to directly detect the first steps of NPF of molecular clusters (~1-2 nm in diameter) and to calculate quantities such as the formation and growth rates of these clusters. Whereas previous studies reported particle formation rates as the flux of particles across a specified particle diameter or calculated them from measurements of larger particle sizes, this protocol outlines methods to directly quantify particle dynamics for cluster sizes. Here, we describe the instrumentation and analysis methods needed to quantify particle dynamics during NPF of sub-3-nm aerosol particles in chamber experiments. The methods described in this protocol can be used to make results from different chamber experiments comparable. The experimental setup, collection and post-processing of the data, and thus completion of this protocol, take from months up to years, depending on the chamber facility, experimental plan and level of expertise. Use of this protocol requires engineering capabilities and expertise in data analysis.
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http://dx.doi.org/10.1038/s41596-019-0274-zDOI Listing
March 2020

Input-Adaptive Proxy for Black Carbon as a Virtual Sensor.

Sensors (Basel) 2019 Dec 28;20(1). Epub 2019 Dec 28.

Institute for Atmospheric and Earth System Research (INAR)/Physics, University of Helsinki, FI-00560 Helsinki, Finland.

Missing data has been a challenge in air quality measurement. In this study, we develop an input-adaptive proxy, which selects input variables of other air quality variables based on their correlation coefficients with the output variable. The proxy uses ordinary least squares regression model with robust optimization and limits the input variables to a maximum of three to avoid overfitting. The adaptive proxy learns from the data set and generates the best model evaluated by adjusted coefficient of determination (adjR). In case of missing data in the input variables, the proposed adaptive proxy then uses the second-best model until all the missing data gaps are filled up. We estimated black carbon (BC) concentration by using the input-adaptive proxy in two sites in Helsinki, which respectively represent street canyon and urban background scenario, as a case study. Accumulation mode, traffic counts, nitrogen dioxide and lung deposited surface area are found as input variables in models with the top rank. In contrast to traditional proxy, which gives 20-80% of data, the input-adaptive proxy manages to give full continuous BC estimation. The newly developed adaptive proxy also gives generally accurate BC (street canyon: adjR = 0.86-0.94; urban background: adjR = 0.74-0.91) depending on different seasons and day of the week. Due to its flexibility and reliability, the adaptive proxy can be further extend to estimate other air quality parameters. It can also act as an air quality virtual sensor in support with on-site measurements in the future.
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http://dx.doi.org/10.3390/s20010182DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6982708PMC
December 2019

Source apportionment of particle number size distribution in urban background and traffic stations in four European cities.

Environ Int 2020 02 4;135:105345. Epub 2019 Dec 4.

MRC-PHE Centre for Environment and Health, Environmental Research Group, King's College London, 150 Stamford Street, London SE1 9NH, UK.

Ultrafine particles (UFP) are suspected of having significant impacts on health. However, there have only been a limited number of studies on sources of UFP compared to larger particles. In this work, we identified and quantified the sources and processes contributing to particle number size distributions (PNSD) using Positive Matrix Factorization (PMF) at six monitoring stations (four urban background and two street canyon) from four European cities: Barcelona, Helsinki, London, and Zurich. These cities are characterised by different meteorological conditions and emissions. The common sources across all stations were Photonucleation, traffic emissions (3 sources, from fresh to aged emissions: Traffic nucleation, Fresh traffic - mode diameter between 13 and 37 nm, and Urban - mode diameter between 44 and 81 nm, mainly traffic but influenced by other sources in some cities), and Secondary particles. The Photonucleation factor was only directly identified by PMF for Barcelona, while an additional split of the Nucleation factor (into Photonucleation and Traffic nucleation) by using NO concentrations as a proxy for traffic emissions was performed for all other stations. The sum of all traffic sources resulted in a maximum relative contributions ranging from 71 to 94% (annual average) thereby being the main contributor at all stations. In London and Zurich, the relative contribution of the sources did not vary significantly between seasons. In contrast, the high levels of solar radiation in Barcelona led to an important contribution of Photonucleation particles (ranging from 14% during the winter period to 35% during summer). Biogenic emissions were a source identified only in Helsinki (both in the urban background and street canyon stations), that contributed importantly during summer (23% in urban background). Airport emissions contributed to Nucleation particles at urban background sites, as the highest concentrations of this source took place when the wind was blowing from the airport direction in all cities.
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http://dx.doi.org/10.1016/j.envint.2019.105345DOI Listing
February 2020

Exploring the regional pollution characteristics and meteorological formation mechanism of PM in North China during 2013-2017.

Environ Int 2020 01 16;134:105283. Epub 2019 Nov 16.

State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China; Centre for Excellence in Atmospheric Urban Environment, Institute of Urban Environment, Chinese Academy of Science, Xiamen, Fujian 361021, China; University of the Chinese Academy of Sciences, Beijing 100049, China; Department of Atmospheric Physics, Nanjing University of Information Science & Technology, Nanjing 210044, China.

In the last decade, North China (NC) has been one of the most populated and polluted regions in the world. The regional air pollution has had a serious impact on people's health; thus, all levels of government have implemented various pollution prevention measures since 2013. Based on multi-city in situ environmental and meteorological data, as well as the meteorological reanalysis dataset from 2013 to 2017, regional pollution characteristics and meteorological formation mechanisms were analyzed to provide a more comprehensive understanding of the evolution of PM in NC. The domain-averaged PM was 79 ± 17 µg m from 2013 to 2017, with a decreasing rate of 10 μg m yr. Two automatic computer algorithms were established to identify 6 daily regional pollution types (DRPTs) and 48 persistent regional pollution events (PRPEs) over NC during 2014-2017. The average PM concentration for the Large-Region-Pollution type (including the Large-Moderate-Region-Pollution and Large-Severe-Region-Pollution types) was 113 ± 40 µg m, and more than half of Large-Region-Pollution days and PRPEs occurred in winter. The PRPEs in NC mainly developed from the area south of Hebei. The number of Large-Region-Pollution days decreased notably from 2014 to 2017, the annual number of days varying between 194 and 97 days, whereas a slight decline was observed in winter. In addition, the averaged PM concentrations and the numbers and durations of the PRPEs decreased. Lamb-Jenkinson weather typing was used to reveal the impact of synoptic circulations on PM across NC. Generally, the contributions of the variations in circulation to the reduction in PM levels over NC between 2013 and 2017 were 64% and 45% in summer and winter, respectively. The three most highly polluted weather types were types C, S and E, with an average PM concentration of 137 ± 40 µg m in winter. Furthermore, three typical circulation dynamics were categorized in the peak stage of the PRPEs, namely, the southerly airflow pattern, the northerly airflow pattern and anticyclone pattern; the averaged relative humidity, recirculation index, wind speed and boundary layer height were 63%, 0.33, 2.0 m s and 493 m, respectively. Our results imply that additional emission reduction measures should be implemented under unfavorable meteorological situations to attain ambient air quality standards in the future.
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http://dx.doi.org/10.1016/j.envint.2019.105283DOI Listing
January 2020

Molecular identification of organic vapors driving atmospheric nanoparticle growth.

Nat Commun 2019 09 30;10(1):4442. Epub 2019 Sep 30.

Department of Applied Physics, University of Eastern Finland, 70211, Kuopio, Finland.

Particles formed in the atmosphere via nucleation provide about half the number of atmospheric cloud condensation nuclei, but in many locations, this process is limited by the growth of the newly formed particles. That growth is often via condensation of organic vapors. Identification of these vapors and their sources is thus fundamental for simulating changes to aerosol-cloud interactions, which are one of the most uncertain aspects of anthropogenic climate forcing. Here we present direct molecular-level observations of a distribution of organic vapors in a forested environment that can explain simultaneously observed atmospheric nanoparticle growth from 3 to 50 nm. Furthermore, the volatility distribution of these vapors is sufficient to explain nanoparticle growth without invoking particle-phase processes. The agreement between observed mass growth, and the growth predicted from the observed mass of condensing vapors in a forested environment thus represents an important step forward in the characterization of atmospheric particle growth.
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http://dx.doi.org/10.1038/s41467-019-12473-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6769005PMC
September 2019

The role of highly oxygenated organic molecules in the Boreal aerosol-cloud-climate system.

Nat Commun 2019 09 25;10(1):4370. Epub 2019 Sep 25.

Institute for Atmospheric and Earth System Research (physics), University of Helsinki, P.O. Box 64, FI-00014, Helsinki, Finland.

Over Boreal regions, monoterpenes emitted from the forest are the main precursors for secondary organic aerosol (SOA) formation and the primary driver of the growth of new aerosol particles to climatically important cloud condensation nuclei (CCN). Autoxidation of monoterpenes leads to rapid formation of Highly Oxygenated organic Molecules (HOM). We have developed the first model with near-explicit representation of atmospheric new particle formation (NPF) and HOM formation. The model can reproduce the observed NPF, HOM gas-phase composition and SOA formation over the Boreal forest. During the spring, HOM SOA formation increases the CCN concentration by ~10 % and causes a direct aerosol radiative forcing of -0.10 W/m. In contrast, NPF reduces the number of CCN at updraft velocities < 0.2 m/s, and causes a direct aerosol radiative forcing of +0.15 W/m. Hence, while HOM SOA contributes to climate cooling, NPF can result in climate warming over the Boreal forest.
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http://dx.doi.org/10.1038/s41467-019-12338-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6761173PMC
September 2019

Molecular Composition and Volatility of Nucleated Particles from α-Pinene Oxidation between -50 °C and +25 °C.

Environ Sci Technol 2019 Nov 8;53(21):12357-12365. Epub 2019 Oct 8.

Center for Atmospheric Particle Studies , Carnegie Mellon University , Pittsburgh , Pennsylvania 15213 , United States.

We use a real-time temperature-programmed desorption chemical-ionization mass spectrometer (FIGAERO-CIMS) to measure particle-phase composition and volatility of nucleated particles, studying pure α-pinene oxidation over a wide temperature range (-50 °C to +25 °C) in the CLOUD chamber at CERN. Highly oxygenated organic molecules are much more abundant in particles formed at higher temperatures, shifting the compounds toward higher O/C and lower intrinsic (300 K) volatility. We find that pure biogenic nucleation and growth depends only weakly on temperature. This is because the positive temperature dependence of degree of oxidation (and polarity) and the negative temperature dependence of volatility counteract each other. Unlike prior work that relied on estimated volatility, we directly measure volatility via calibrated temperature-programmed desorption. Our particle-phase measurements are consistent with gas-phase results and indicate that during new-particle formation from α-pinene oxidation, gas-phase chemistry directly determines the properties of materials in the condensed phase. We now have consistency between measured gas-phase product concentrations, product volatility, measured and modeled growth rates, and the particle composition over most temperatures found in the troposphere.
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http://dx.doi.org/10.1021/acs.est.9b03265DOI Listing
November 2019

Radical Formation by Fine Particulate Matter Associated with Highly Oxygenated Molecules.

Environ Sci Technol 2019 Nov 7;53(21):12506-12518. Epub 2019 Oct 7.

Centre for Atmospheric Science, Department of Chemistry , University of Cambridge , Cambridge CB2 1EW , United Kingdom.

Highly oxygenated molecules (HOMs) play an important role in the formation and evolution of secondary organic aerosols (SOA). However, the abundance of HOMs in different environments and their relation to the oxidative potential of fine particulate matter (PM) are largely unknown. Here, we investigated the relative HOM abundance and radical yield of laboratory-generated SOA and fine PM in ambient air ranging from remote forest areas to highly polluted megacities. By electron paramagnetic resonance and mass spectrometric investigations, we found that the relative abundance of HOMs, especially the dimeric and low-volatility types, in ambient fine PM was positively correlated with the formation of radicals in aqueous PM extracts. SOA from photooxidation of isoprene, ozonolysis of α- and β-pinene, and fine PM from tropical (central Amazon) and boreal (Hyytiälä, Finland) forests exhibited a higher HOM abundance and radical yield than SOA from photooxidation of naphthalene and fine PM from urban sites (Beijing, Guangzhou, Mainz, Shanghai, and Xi'an), confirming that HOMs are important constituents of biogenic SOA to generate radicals. Our study provides new insights into the chemical relationship of HOM abundance, composition, and sources with the yield of radicals by laboratory and ambient aerosols, enabling better quantification of the component-specific contribution of source- or site-specific fine PM to its climate and health effects.
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http://dx.doi.org/10.1021/acs.est.9b05149DOI Listing
November 2019

Ultrafine particles and PM in the air of cities around the world: Are they representative of each other?

Environ Int 2019 08 21;129:118-135. Epub 2019 May 21.

International Laboratory for Air Quality and Health, Queensland University of Technology, Brisbane, QLD 4000, Australia. Electronic address:

Can mitigating only particle mass, as the existing air quality measures do, ultimately lead to reduction in ultrafine particles (UFP)? The aim of this study was to provide a broader urban perspective on the relationship between UFP, measured in terms of particle number concentration (PNC) and PM (mass concentration of particles with aerodynamic diameter < 2.5 μm) and factors that influence their concentrations. Hourly average PNC and PM were acquired from 10 cities located in North America, Europe, Asia, and Australia over a 12-month period. A pairwise comparison of the mean difference and the Kolmogorov-Smirnov test with the application of bootstrapping were performed for each city. Diurnal and seasonal trends were obtained using a generalized additive model (GAM). The particle number to mass concentration ratios and the Pearson's correlation coefficient were calculated to elucidate the nature of the relationship between these two metrics. Results show that the annual mean concentrations ranged from 8.0 × 10 to 19.5 × 10 particles·cm and from 7.0 to 65.8 μg·m for PNC and PM, respectively, with the data distributions generally skewed to the right, and with a wider spread for PNC. PNC showed a more distinct diurnal trend compared with PM, attributed to the high contributions of UFP from vehicular emissions to PNC. The variation in both PNC and PM due to seasonality is linked to the cities' geographical location and features. Clustering the cities based on annual median concentrations of both PNC and PM demonstrated that a high PNC level does not lead to a high PM, and vice versa. The particle number-to-mass ratio (in units of 10 particles·μg) ranged from 0.14 to 2.2, >1 for roadside sites and <1 for urban background sites with lower values for more polluted cities. The Pearson's r ranged from 0.09 to 0.64 for the log-transformed data, indicating generally poor linear correlation between PNC and PM. Therefore, PNC and PM measurements are not representative of each other; and regulating PM does little to reduce PNC. This highlights the need to establish regulatory approaches and control measures to address the impacts of elevated UFP concentrations, especially in urban areas, considering their potential health risks.
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http://dx.doi.org/10.1016/j.envint.2019.05.021DOI Listing
August 2019

Ion Mobility-Mass Spectrometry of Iodine Pentoxide-Iodic Acid Hybrid Cluster Anions in Dry and Humidified Atmospheres.

J Phys Chem Lett 2019 Apr 8;10(8):1935-1941. Epub 2019 Apr 8.

Department of Mechanical Engineering , University of Minnesota , Minneapolis , Minnesota 55455 , United States.

Nanometer-scale clusters form from vapor-phase precursors and can subsequently grow into nanoparticles during atmospheric nucleation events. A particularly interesting set of clusters relevant to nucleation is hybrid iodine pentoxide-iodic acid clusters of the form (IO) (HIO) as these clusters have been observed in coastal region nucleation events in anomalously high concentrations. To better understand their properties, we utilized ion mobility-mass spectrometry to probe the structures of cluster anions of the form (IO) (HIO) (IO) ( x = 0-7, y = 0-1, α = 1-3), similar to those observed in coastal nucleation events. We show that (IO) (HIO) (IO) clusters are relatively stable against dissociation during mass spectrometric measurement, as compared to other clusters observed in nucleation events over continental sites, and that at atmospherically relevant relative humidity levels (65% and less) clusters can become sufficiently hydrated to facilitate complete conversion of iodine pentoxide to iodic acid but that water sorption beyond this level is limited, indicating that the clusters do not persist as nanometer-scale droplets in the ambient.
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http://dx.doi.org/10.1021/acs.jpclett.9b00453DOI Listing
April 2019

Highly Oxygenated Organic Molecules (HOM) from Gas-Phase Autoxidation Involving Peroxy Radicals: A Key Contributor to Atmospheric Aerosol.

Chem Rev 2019 03 25;119(6):3472-3509. Epub 2019 Feb 25.

Institute for Atmospheric and Earth System Research, Faculty of Science , University of Helsinki , Helsinki 00014 , Finland.

Highly oxygenated organic molecules (HOM) are formed in the atmosphere via autoxidation involving peroxy radicals arising from volatile organic compounds (VOC). HOM condense on pre-existing particles and can be involved in new particle formation. HOM thus contribute to the formation of secondary organic aerosol (SOA), a significant and ubiquitous component of atmospheric aerosol known to affect the Earth's radiation balance. HOM were discovered only very recently, but the interest in these compounds has grown rapidly. In this Review, we define HOM and describe the currently available techniques for their identification/quantification, followed by a summary of the current knowledge on their formation mechanisms and physicochemical properties. A main aim is to provide a common frame for the currently quite fragmented literature on HOM studies. Finally, we highlight the existing gaps in our understanding and suggest directions for future HOM research.
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http://dx.doi.org/10.1021/acs.chemrev.8b00395DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6439441PMC
March 2019

Multicomponent new particle formation from sulfuric acid, ammonia, and biogenic vapors.

Sci Adv 2018 Dec 12;4(12):eaau5363. Epub 2018 Dec 12.

Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland.

A major fraction of atmospheric aerosol particles, which affect both air quality and climate, form from gaseous precursors in the atmosphere. Highly oxygenated organic molecules (HOMs), formed by oxidation of biogenic volatile organic compounds, are known to participate in particle formation and growth. However, it is not well understood how they interact with atmospheric pollutants, such as nitrogen oxides (NO ) and sulfur oxides (SO ) from fossil fuel combustion, as well as ammonia (NH) from livestock and fertilizers. Here, we show how NO suppresses particle formation, while HOMs, sulfuric acid, and NH have a synergistic enhancing effect on particle formation. We postulate a novel mechanism, involving HOMs, sulfuric acid, and ammonia, which is able to closely reproduce observations of particle formation and growth in daytime boreal forest and similar environments. The findings elucidate the complex interactions between biogenic and anthropogenic vapors in the atmospheric aerosol system.
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http://dx.doi.org/10.1126/sciadv.aau5363DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6291317PMC
December 2018

Seasonal influences on surface ozone variability in continental South Africa and implications for air quality.

Atmos Chem Phys 2018 Oct 29;18(20):15491-15514. Epub 2018 Oct 29.

Finnish Meteorological Institute, Helsinki, Finland.

Although elevated surface ozone (O) concentrations are observed in many areas within southern Africa, few studies have investigated the regional atmospheric chemistry and dominant atmospheric processes driving surface O formation in this region. Therefore, an assessment of comprehensive continuous surface O measurements performed at four sites in continental South Africa was conducted. The regional O problem was evident, with O concentrations regularly exceeding the South African air quality standard limit, while O levels were higher compared to other background sites in the Southern Hemisphere. The temporal O patterns observed at the four sites resembled typical trends for O in continental South Africa, with O concentrations peaking in late winter and early spring. Increased O concentrations in winter were indicative of increased emissions of O precursors from household combustion and other low-level sources, while a spring maximum observed at all the sites was attributed to increased regional biomass burning. Source area maps of O and CO indicated significantly higher O and CO concentrations associated with air masses passing over a region with increased seasonal open biomass burning, which indicated CO associated with open biomass burning as a major source of O in continental South Africa. A strong correlation between O on CO was observed, while O levels remained relatively constant or decreased with increasing NO , which supports a VOC-limited regime. The instantaneous production rate of O calculated at Welgegund indicated that ~ 40 % of O production occurred in the VOC-limited regime. The relationship between O and precursor species suggests that continental South Africa can be considered VOC limited, which can be attributed to high anthropogenic emissions of NO in the interior of South Africa. The study indicated that the most effective emission control strategy to reduce O levels in continental South Africa should be CO and VOC reduction, mainly associated with household combustion and regional open biomass burning.
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http://dx.doi.org/10.5194/acp-18-15491-2018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7365263PMC
October 2018

Accretion Product Formation from Ozonolysis and OH Radical Reaction of α-Pinene: Mechanistic Insight and the Influence of Isoprene and Ethylene.

Environ Sci Technol 2018 10 20;52(19):11069-11077. Epub 2018 Sep 20.

Institute for Ion Physics and Applied Physics , University of Innsbruck , 6020 Innsbruck , Austria.

α-Pinene (CH) represents one of the most important biogenic emissions in the atmosphere. Its oxidation products can significantly contribute to the secondary organic aerosol (SOA) formation. Here, we report on the formation mechanism of C and C accretion products from α-pinene oxidation, which are believed to be efficient SOA precursors. Measurements have been performed in a free-jet flow system. Detection of RO radicals and accretion products was carried out by recent mass spectrometric techniques using different ionization schemes. Observed C-RO radicals from α-pinene ozonolysis were O,O-CH(O) O with x = 0, 1, 2, 3 and from the OH radical reaction HO-CH(O)O with α = 0, 1, 2. All detected C accretion products can be explained via the accretion reaction RO + R'O → ROOR' + O starting from the measured C-RO radicals. We speculate that C accretion products are formed in an analogous way assuming CHO elimination. Addition of isoprene (CH), producing C-RO radicals, leads to C accretion products formed via cross-reactions with C-RO radicals. This process is competing with the formation of C/C products from the pure α-pinene oxidation. A similar behavior has been observed for ethylene additives that form C accretion products. In the atmosphere, a complex accretion product spectrum from self- and cross-reactions of available RO radicals can be expected. Modeling atmospheric conditions revealed that C/C product formation is only reduced by a factor of 1.2 or 3.6 in isoprene-dominated environments assuming a 2- or 15-fold isoprene concentration over α-pinene, respectively, as present in different forested areas.
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http://dx.doi.org/10.1021/acs.est.8b02210DOI Listing
October 2018

Rapid growth of organic aerosol nanoparticles over a wide tropospheric temperature range.

Proc Natl Acad Sci U S A 2018 09 28;115(37):9122-9127. Epub 2018 Aug 28.

Faculty of Physics, University of Vienna, 1090 Vienna, Austria;

Nucleation and growth of aerosol particles from atmospheric vapors constitutes a major source of global cloud condensation nuclei (CCN). The fraction of newly formed particles that reaches CCN sizes is highly sensitive to particle growth rates, especially for particle sizes <10 nm, where coagulation losses to larger aerosol particles are greatest. Recent results show that some oxidation products from biogenic volatile organic compounds are major contributors to particle formation and initial growth. However, whether oxidized organics contribute to particle growth over the broad span of tropospheric temperatures remains an open question, and quantitative mass balance for organic growth has yet to be demonstrated at any temperature. Here, in experiments performed under atmospheric conditions in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN), we show that rapid growth of organic particles occurs over the range from [Formula: see text]C to [Formula: see text]C. The lower extent of autoxidation at reduced temperatures is compensated by the decreased volatility of all oxidized molecules. This is confirmed by particle-phase composition measurements, showing enhanced uptake of relatively less oxygenated products at cold temperatures. We can reproduce the measured growth rates using an aerosol growth model based entirely on the experimentally measured gas-phase spectra of oxidized organic molecules obtained from two complementary mass spectrometers. We show that the growth rates are sensitive to particle curvature, explaining widespread atmospheric observations that particle growth rates increase in the single-digit-nanometer size range. Our results demonstrate that organic vapors can contribute to particle growth over a wide range of tropospheric temperatures from molecular cluster sizes onward.
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http://dx.doi.org/10.1073/pnas.1807604115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6140529PMC
September 2018

Atmospheric new particle formation from sulfuric acid and amines in a Chinese megacity.

Science 2018 07;361(6399):278-281

Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP), Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China.

Atmospheric new particle formation (NPF) is an important global phenomenon that is nevertheless sensitive to ambient conditions. According to both observation and theoretical arguments, NPF usually requires a relatively high sulfuric acid (HSO) concentration to promote the formation of new particles and a low preexisting aerosol loading to minimize the sink of new particles. We investigated NPF in Shanghai and were able to observe both precursor vapors (HSO) and initial clusters at a molecular level in a megacity. High NPF rates were observed to coincide with several familiar markers suggestive of HSO-dimethylamine (DMA)-water (HO) nucleation, including sulfuric acid dimers and HSO-DMA clusters. In a cluster kinetics simulation, the observed concentration of sulfuric acid was high enough to explain the particle growth to ~3 nanometers under the very high condensation sink, whereas the subsequent higher growth rate beyond this size is believed to result from the added contribution of condensing organic species. These findings will help in understanding urban NPF and its air quality and climate effects, as well as in formulating policies to mitigate secondary particle formation in China.
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http://dx.doi.org/10.1126/science.aao4839DOI Listing
July 2018