Publications by authors named "Urs Baltensperger"

88 Publications

Photodegradation of α-Pinene Secondary Organic Aerosol Dominated by Moderately Oxidized Molecules.

Environ Sci Technol 2021 May 7;55(10):6936-6943. Epub 2021 May 7.

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland.

Atmospheric secondary organic aerosol (SOA) undergoes chemical and physical changes when exposed to UV radiation, affecting the atmospheric lifetime of the involved molecules. However, these photolytic processes remain poorly constrained. Here, we present a study aimed at characterizing, at a molecular level and in real time, the chemical composition of α-pinene SOA exposed to UV-A light at 50% relative humidity in an atmospheric simulation chamber. Significant SOA mass loss is observed at high loadings (∼100 μg m), whereas the effect is less prevalent at lower loadings (∼20 μg m). For the vast majority of molecules measured by the extractive electrospray time-of-flight mass spectrometer, there is a fraction that is photoactive and decays when exposed to UV-A radiation and a fraction that appears photorecalcitrant. The molecules that are most photoactive contain between 4 and 6 oxygen atoms, while the more highly oxygenated compounds and dimers do not exhibit significant decay. Overall, photolysis results in a reduction of the volatility of SOA, which cannot be explained by simple evaporative losses but requires either a change in volatility related to changes in functional groups or a change in physical parameters (i.e., viscosity).
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http://dx.doi.org/10.1021/acs.est.0c06752DOI Listing
May 2021

Brown Carbon in Primary and Aged Coal Combustion Emission.

Environ Sci Technol 2021 05 7;55(9):5701-5710. Epub 2021 Apr 7.

Centre for Isotope Research (CIO), Energy and Sustainability Research Institute Groningen (ESRIG), University of Groningen, 9747 AG Groningen, The Netherlands.

Smog chamber experiments were conducted to characterize the light absorption of brown carbon (BrC) from primary and photochemically aged coal combustion emissions. Light absorption was measured by the UV-visible spectrophotometric analysis of water and methanol extracts of filter samples. The single-scattering albedo at 450 nm was 0.73 ± 0.10 for primary emissions and 0.75 ± 0.13 for aged emissions. The light absorption coefficient at 365 nm of methanol extracts was higher than that of water extracts by a factor of 10 for primary emissions and a factor of 7 for aged emissions. This suggests that the majority of BrC is water-insoluble even after aging. The mass absorption efficiency of this BrC (MAE) for primary OA (POA) was dependent on combustion conditions, with an average of 0.84 ± 0.54 m g, which was significantly higher than that for aged OA (0.24 ± 0.18 m g). Secondary OA (SOA) dominated aged OA and the decreased MAE after aging indicates that SOA is less light absorbing than POA and/or that BrC is bleached (oxidized) with aging. The estimated MAE of SOA (0.14 ± 0.08 m g) was much lower than that of POA. A comparison of MAE of residential coal combustion with other anthropogenic sources suggests that residential coal combustion emissions are among the strongest absorbing BrC organics.
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http://dx.doi.org/10.1021/acs.est.0c08084DOI Listing
May 2021

Large contribution to secondary organic aerosol from isoprene cloud chemistry.

Sci Adv 2021 Mar 24;7(13). Epub 2021 Mar 24.

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland.

Aerosols still present the largest uncertainty in estimating anthropogenic radiative forcing. Cloud processing is potentially important for secondary organic aerosol (SOA) formation, a major aerosol component: however, laboratory experiments fail to mimic this process under atmospherically relevant conditions. We developed a wetted-wall flow reactor to simulate aqueous-phase processing of isoprene oxidation products (iOP) in cloud droplets. We find that 50 to 70% (in moles) of iOP partition into the aqueous cloud phase, where they rapidly react with OH radicals, producing SOA with a molar yield of 0.45 after cloud droplet evaporation. Integrating our experimental results into a global model, we show that clouds effectively boost the amount of SOA. We conclude that, on a global scale, cloud processing of iOP produces 6.9 Tg of SOA per year or approximately 20% of the total biogenic SOA burden and is the main source of SOA in the mid-troposphere (4 to 6 km).
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http://dx.doi.org/10.1126/sciadv.abe2952DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7990335PMC
March 2021

Characteristics and sources of hourly elements in PM and PM during wintertime in Beijing.

Environ Pollut 2021 Jun 3;278:116865. Epub 2021 Mar 3.

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232, Villigen, PSI, Switzerland. Electronic address:

Characteristics and sources of ambient particle elements in urban Beijing were studied by hourly observations in two size fractions (PM and PM) during November and December 2017 using an online multi-element analyzer. The reconstructed oxide concentrations of 24 elements (from Al to Pb) comprise an appreciable fraction of PM and PM accounting for 37% and 17%, respectively on average. We demonstrate the benefit of using high-time-resolution chemical speciation data in achieving robust source apportionment of the total elemental PM (PM) and elemental PM (PM) mass using positive matrix factorization (PMF). Biomass burning, coal combustion, secondary sulfate, industry, non-exhaust traffic and dust were identified in both size fractions (with varying relative concentrations), which accounted on average for 4%, 12%, 5%, 2%, 14%, and 63%, respectively to the total PM, and 14%, 35%, 21%, 6%, 12% and 12%, respectively to the total PM. Biomass burning and coal combustion exhibited higher concentrations during haze episodes of the heating season. In contrast, secondary sulfate and industry contributed more to haze episodes during the non-heating season. The fractional contribution of dust was mostly high during clean days, while the fractional non-exhaust traffic emission contribution was similar throughout the measurement period. The non-exhaust traffic emissions contributed locally, while the remaining sources were dominated by neighboring areas. Furthermore, trajectory analysis showed that the origin of the industrial sources roughly agreed with the locations of the main point sources. Overall, this work provides detailed information on the characteristics of the elements during different haze events during heating and non-heating seasons.
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http://dx.doi.org/10.1016/j.envpol.2021.116865DOI Listing
June 2021

Role of iodine oxoacids in atmospheric aerosol nucleation.

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

Department of Chemistry and Cooperative Institute for Research in the Environmental Sciences, University of Colorado Boulder, Boulder, CO 80309, USA.

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

Structures and reactivity of peroxy radicals and dimeric products revealed by online tandem mass spectrometry.

Nat Commun 2021 01 12;12(1):300. Epub 2021 Jan 12.

Univ Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, 69626, Villeurbanne, France.

Organic peroxy radicals (RO) play a pivotal role in the degradation of hydrocarbons. The autoxidation of atmospheric RO radicals produces highly oxygenated organic molecules (HOMs), including low-volatility ROOR dimers formed by bimolecular RO + RO reactions. HOMs can initiate and greatly contribute to the formation and growth of atmospheric particles. As a result, HOMs have far-reaching health and climate implications. Nevertheless, the structures and formation mechanism of RO radicals and HOMs remain elusive. Here, we present the in-situ characterization of RO and dimer structure in the gas-phase, using online tandem mass spectrometry analyses. In this study, we constrain the structures and formation pathway of several HOM-RO radicals and dimers produced from monoterpene ozonolysis, a prominent atmospheric oxidation process. In addition to providing insights into atmospheric HOM chemistry, this study debuts online tandem MS analyses as a unique approach for the chemical characterization of reactive compounds, e.g., organic radicals.
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http://dx.doi.org/10.1038/s41467-020-20532-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7804243PMC
January 2021

Sources of particulate-matter air pollution and its oxidative potential in Europe.

Nature 2020 11 18;587(7834):414-419. Epub 2020 Nov 18.

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland.

Particulate matter is a component of ambient air pollution that has been linked to millions of annual premature deaths globally. Assessments of the chronic and acute effects of particulate matter on human health tend to be based on mass concentration, with particle size and composition also thought to play a part. Oxidative potential has been suggested to be one of the many possible drivers of the acute health effects of particulate matter, but the link remains uncertain. Studies investigating the particulate-matter components that manifest an oxidative activity have yielded conflicting results. In consequence, there is still much to be learned about the sources of particulate matter that may control the oxidative potential concentration. Here we use field observations and air-quality modelling to quantify the major primary and secondary sources of particulate matter and of oxidative potential in Europe. We find that secondary inorganic components, crustal material and secondary biogenic organic aerosols control the mass concentration of particulate matter. By contrast, oxidative potential concentration is associated mostly with anthropogenic sources, in particular with fine-mode secondary organic aerosols largely from residential biomass burning and coarse-mode metals from vehicular non-exhaust emissions. Our results suggest that mitigation strategies aimed at reducing the mass concentrations of particulate matter alone may not reduce the oxidative potential concentration. If the oxidative potential can be linked to major health impacts, it may be more effective to control specific sources of particulate matter rather than overall particulate mass.
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http://dx.doi.org/10.1038/s41586-020-2902-8DOI Listing
November 2020

Oxidative stress-induced inflammation in susceptible airways by anthropogenic aerosol.

PLoS One 2020 18;15(11):e0233425. Epub 2020 Nov 18.

Institute of Anatomy, University of Bern, Bern, Switzerland.

Ambient air pollution is one of the leading five health risks worldwide. One of the most harmful air pollutants is particulate matter (PM), which has different physical characteristics (particle size and number, surface area and morphology) and a highly complex and variable chemical composition. Our goal was first to comparatively assess the effects of exposure to PM regarding cytotoxicity, release of pro-inflammatory mediators and gene expression in human bronchial epithelia (HBE) reflecting normal and compromised health status. Second, we aimed at evaluating the impact of various PM components from anthropogenic and biogenic sources on the cellular responses. Air-liquid interface (ALI) cultures of fully differentiated HBE derived from normal and cystic fibrosis (CF) donor lungs were exposed at the apical cell surface to water-soluble PM filter extracts for 4 h. The particle dose deposited on cells was 0.9-2.5 and 8.8-25.4 μg per cm2 of cell culture area for low and high PM doses, respectively. Both normal and CF HBE show a clear dose-response relationship with increasing cytotoxicity at higher PM concentrations. The concurrently enhanced release of pro-inflammatory mediators at higher PM exposure levels links cytotoxicity to inflammatory processes. Further, the PM exposure deregulates genes involved in oxidative stress and inflammatory pathways leading to an imbalance of the antioxidant system. Moreover, we identify compromised defense against PM in CF epithelia promoting exacerbation and aggravation of disease. We also demonstrate that the adverse health outcome induced by PM exposure in normal and particularly in susceptible bronchial epithelia is magnified by anthropogenic PM components. Thus, including health-relevant PM components in regulatory guidelines will result in substantial human health benefits and improve protection of the vulnerable population.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0233425PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7673561PMC
December 2020

Real-time measurement and source apportionment of elements in Delhi's atmosphere.

Sci Total Environ 2020 Nov 23;742:140332. Epub 2020 Jun 23.

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland. Electronic address:

Delhi, the capital of India, suffers from heavy local emissions as well as regional transport of air pollutants, resulting in severe aerosol loadings. To determine the sources of these pollutants, we have quantified the mass concentrations of 26 elements in airborne particles, measured by an online X-ray fluorescence spectrometer with time resolution between 30 min and 1 h. Measurements of PM and PM (particulate matter <10 μm and < 2.5 μm) were conducted during two consecutive winters (2018 and 2019) in Delhi. On average, 26 elements from Al to Pb made up ~25% and ~19% of the total PM mass (271 μg m and 300 μg m) in 2018 and 2019, respectively. Nine different aerosol sources were identified during both winters using positive matrix factorization (PMF), including dust, non-exhaust, an S-rich factor, two solid fuel combustion (SFC) factors and four industrial/combustion factors related to plume events (Cr-Ni-Mn, Cu-Cd-Pb, Pb-Sn-Se and Cl-Br-Se). All factors were resolved in both size ranges (but varying relative concentrations), comprising the following contributions to the elemental PM mass (in % average for 2018 and 2019): Cl-Br-Se (41.5%, 36.9%), dust (27.6%, 28.7%), non-exhaust (16.2%, 13.7%), S-rich (6.9%, 9.2%), SFC1 + SFC2 (4%, 7%), Pb-Sn-Se (2.3%, 1.66%), Cu-Cd-Pb (0.67%, 2.2%) and Cr-Ni-Mn (0.57%, 0.47%). Most of these sources had the highest relative contributions during late night (22:00 local time (LT)) and early morning hours (between 03:00 to 08:00 LT), which is consistent with enhanced emissions into a shallow boundary layer. Modelling of airmass source geography revealed that the Pb-Sn-Se, Cl-Br-Se and SFC2 factors prevailed for northwest winds (Pakistan, Punjab, Haryana and Delhi), while the Cu-Cd-Pb and S-rich factors originated from east (Nepal and Uttar Pradesh) and the Cr-Ni-Mn factor from northeast (Uttar Pradesh). In contrast, SFC1, dust and non-exhaust were not associated with any specific wind direction.
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http://dx.doi.org/10.1016/j.scitotenv.2020.140332DOI Listing
November 2020

Publisher Correction: Frequent new particle formation over the high Arctic pack ice by enhanced iodine emissions.

Nat Commun 2020 Oct 28;11(1):5557. Epub 2020 Oct 28.

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, PSI, Switzerland.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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http://dx.doi.org/10.1038/s41467-020-19533-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7595227PMC
October 2020

Online monitoring of volatile organic compounds emitted from human bronchial epithelial cells as markers for oxidative stress.

J Breath Res 2020 Oct 12. Epub 2020 Oct 12.

Paul Scherrer Institute Laboratory of Atmospheric Chemistry, Villigen, 5232, SWITZERLAND.

Particulate air pollution is associated with adverse respiratory effects and is a major factor for premature deaths. In-vitro assays are commonly used for investigating the direct cytotoxicity and inflammatory impacts due to particulate matter (PM) exposure. However, biological tests are often labor-intensive, destructive and limited to endpoints measured offline at single time points, making it impossible to observe the progression of cell response upon exposure. Here we explored the potential of a high-resolution proton transfer reaction mass spectrometer (PTR-MS) to detect the volatile organic compounds (VOCs) emitted by human bronchial epithelial cells (BEAS-2B) upon exposure to PM. Cells were exposed to single components (1,4-naphthoquinone and Cu(II)) known to induce oxidative stress. We also tested filter extracts of aerosols generated in a smog chamber, including fresh and aged wood burning emissions, as well as α-pinene secondary organic aerosol (SOA). We found that 1,4-naphthoquinone was rapidly internalized by the cells. Exposing cells to each of these samples induced the emission of VOCs, which we tentatively assigned to acetonitrile, benzaldehyde and dimethylbenzaldehyde, respectively. Emission rates upon exposure to fresh and aged organic aerosol from α-pinene oxidation and from biomass burning significantly exceeded those observed after exposure to similar doses of Cu(II), a proxy for transition metals with high oxidative potential. Emission rates of biomarkers from cell exposure to α-pinene SOA exhibited a statistically significant, but weak dose dependence. The emission rates of benzaldehyde scaled with cell death, estimated by measuring the apical release of cytosolic lactate dehydrogenase. Particle mass doses delivered to the BEAS-2B cells match those deposited in the human tracheobronchial tract after several hours of inhalation at elevated ambient air pollution. The results presented here show that our method has the potential to determine biomarkers of PM induced pulmonary damage in toxicological and epidemiological research on air pollution.
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http://dx.doi.org/10.1088/1752-7163/abc055DOI Listing
October 2020

Frequent new particle formation over the high Arctic pack ice by enhanced iodine emissions.

Nat Commun 2020 10 1;11(1):4924. Epub 2020 Oct 1.

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, PSI, Switzerland.

In the central Arctic Ocean the formation of clouds and their properties are sensitive to the availability of cloud condensation nuclei (CCN). The vapors responsible for new particle formation (NPF), potentially leading to CCN, have remained unidentified since the first aerosol measurements in 1991. Here, we report that all the observed NPF events from the Arctic Ocean 2018 expedition are driven by iodic acid with little contribution from sulfuric acid. Iodic acid largely explains the growth of ultrafine particles (UFP) in most events. The iodic acid concentration increases significantly from summer towards autumn, possibly linked to the ocean freeze-up and a seasonal rise in ozone. This leads to a one order of magnitude higher UFP concentration in autumn. Measurements of cloud residuals suggest that particles smaller than 30 nm in diameter can activate as CCN. Therefore, iodine NPF has the potential to influence cloud properties over the Arctic Ocean.
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http://dx.doi.org/10.1038/s41467-020-18551-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7529815PMC
October 2020

Changes in ozone and PM in Europe during the period of 1990-2030: Role of reductions in land and ship emissions.

Sci Total Environ 2020 Nov 23;741:140467. Epub 2020 Jun 23.

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland.

Air pollution is among the top threats to human health and ecosystems despite the substantial decrease in anthropogenic emissions. Meanwhile, the role of ship emissions on air quality is becoming increasingly important with the growing maritime transport and less strict regulations. In this study, we modeled the air quality in Europe between 1990 and 2030 with ten-year intervals, using the regional air quality model CAMx version 6.50, to investigate the changes in the past (1990-2010) as well as the effects of different land and ship emission scenarios in the future (2020,2030). The modeled mean ozone levels decreased slightly during the first decade but then started increasing again especially in polluted areas. Results from the future scenarios suggest that by 2030 the peak ozone would decrease, leading to a decrease in the days exceeding the maximum daily 8-h average ozone (MDA8) limit values (60 ppb) by 51% in southern Europe relative to 1990. The model results show a decrease of 56% (6.3 μg m) in PM concentrations from 1990 to 2030 under current legislation, mostly due to a large drop in sulfate (representing up to 44% of the total PM decrease during 1990-2000) while nitrate concentrations were predicted to go down with an increasing rate (10% of total PM decrease during 1990-2000 while 36% during 2020-2030). The ship emissions if reduced according to the maximum technically feasible reduction (MTFR) scenario were predicted to contribute up to 19% of the decrease in the PM concentrations over land between 2010 and 2030. Ship emission reductions according to the MTFR scenario would lead to a decrease in the days with MDA8 exceeding EU limits by 24-28% (10-14 days) around the coastal regions. The results obtained in our study show the increasing importance of ship emission reductions, after a relatively large decrease in land emissions was achieved in Europe.
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http://dx.doi.org/10.1016/j.scitotenv.2020.140467DOI Listing
November 2020

Chemical characterization of PM and source apportionment of organic aerosol in New Delhi, India.

Sci Total Environ 2020 Nov 13;745:140924. Epub 2020 Jul 13.

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland. Electronic address:

Delhi is one of the most polluted cities worldwide and a comprehensive understanding and deeper insight into the air pollution and its sources is of high importance. We report 5 months of highly time-resolved measurements of non-refractory PM and black carbon (BC). Additionally, source apportionment based on positive matrix factorization (PMF) of the organic aerosol (OA) fraction is presented. The highest pollution levels are observed during winter in December/January. During that time, also uniquely high chloride concentrations are measured, which are sometimes even the most dominant NR-species in the morning hours. With increasing temperature, the total PM concentration decreases steadily, whereas the chloride concentrations decrease sharply. The concentrations measured in May are roughly 6 times lower than in December/January. PMF analysis resolves two primary factors, namely hydrocarbon-like (traffic-related) OA (HOA) and solid fuel combustion OA (SFC-OA), and one or two secondary factors depending on the season. The uncertainties of the PMF analysis are assessed by combining the random a-value approach and the bootstrap resampling technique of the PMF input. The uncertainties for the resolved factors range from ±18% to ±19% for HOA, ±7% to ±19% for SFC-OA and ±6 % to ±11% for the OOAs. The average correlation of HOA with equivalent black carbon from traffic (eBC) is R = 0.40, while SFC-OA has a correlation of R = 0.78 with equivalent black carbon from solid fuel combustion (eBC). Anthracene (m/z 178) and pyrene (m/z 202) (PAHs) are mostly explained by SFC-OA and follow its diurnal trend (R = 0.98 and R = 0.97). The secondary oxygenated aerosols are dominant during daytime. The average contribution during the afternoon hours (1 pm-5 pm) is 59% to the total OA mass, with contributions up to 96% in May. In contrast, the primary sources are more important during nighttime: the mean nightly contribution (22 pm-3 am) to the total OA mass is 48%, with contributions up to 88% during some episodes in April.
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http://dx.doi.org/10.1016/j.scitotenv.2020.140924DOI Listing
November 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.

Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, 60438, Frankfurt am Main, Germany.

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.

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

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

Online Aerosol Chemical Characterization by Extractive Electrospray Ionization-Ultrahigh-Resolution Mass Spectrometry (EESI-Orbitrap).

Environ Sci Technol 2020 04 20;54(7):3871-3880. Epub 2020 Mar 20.

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.

Current mass spectrometry techniques for the online measurement of organic aerosol (OA) composition are subjected to either thermal/ionization-induced artifacts or limited mass resolving power, hindering accurate molecular characterization. Here, we combined the soft ionization capability of extractive electrospray ionization (EESI) and the ultrahigh mass resolution of Orbitrap for real-time, near-molecular characterization of OAs. Detection limits as low as tens of ng m with linearity up to hundreds of μg m at 0.2 Hz time resolution were observed for single- and mixed-component calibrations. The performance of the EESI-Orbitrap system was further evaluated with laboratory-generated secondary OAs (SOAs) and filter extracts of ambient particulate matter. The high mass accuracy and resolution (140 000 at / 200) of the EESI-Orbitrap system enable unambiguous identification of the aerosol components' molecular composition and allow a clear separation between adjacent peaks, which would be significantly overlapping if a medium-resolution (20 000) mass analyzer was used. Furthermore, the tandem mass spectrometry (MS) capability provides valuable insights into the compound structure. For instance, the MS analysis of ambient OA samples and lab-generated biogenic SOAs points to specific SOA precursors in ambient air among a range of possible isomers based on fingerprint fragment ions. Overall, this newly developed and characterized EESI-Orbitrap system will advance our understanding of the formation and evolution of atmospheric aerosols.
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http://dx.doi.org/10.1021/acs.est.9b07090DOI Listing
April 2020

Comparing the lung cancer burden of ambient particulate matter using scenarios of air quality standards versus acceptable risk levels.

Int J Public Health 2020 Mar 7;65(2):139-148. Epub 2020 Jan 7.

Swiss Tropical and Public Health Institute, Basel, Switzerland.

Objectives: Ambient particulate matter (PM) is regulated with science-based air quality standards, whereas carcinogens are regulated with a number of "acceptable" cases. Given that PM is also carcinogenic, we identify differences between approaches.

Methods: We assessed the lung cancer deaths for Switzerland attributable to exposure to PM up to 10 µm (PM) and to five particle-bound carcinogens. For PM, we used an epidemiological approach based on relative risks with four exposure scenarios compared to two counterfactual concentrations. For carcinogens, we used a toxicological approach based on unit risks with four exposure scenarios.

Results: The lung cancer burden using concentrations from 2010 was 10-14 times larger for PM than for the five carcinogens. However, the burden depends on the underlying exposure scenarios, counterfactual concentrations and number of carcinogens. All scenarios of the toxicological approach for five carcinogens result in a lower burden than the epidemiological approach for PM.

Conclusions: Air quality standards-promoted so far by the WHO Air Quality Guidelines-provide a more appealing framework to guide health risk-oriented clean air policymaking than frameworks based on a number of "acceptable" cases.
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http://dx.doi.org/10.1007/s00038-019-01324-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7049545PMC
March 2020

Source apportionment of fine particulate matter in a Middle Eastern Metropolis, Tehran-Iran, using PMF with organic and inorganic markers.

Sci Total Environ 2020 Feb 21;705:135330. Epub 2019 Nov 21.

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen-PSI, Switzerland. Electronic address:

With over 8 million inhabitants and 4 million motor vehicles on the streets, Tehran is one of the most crowded and polluted cities in the Middle East. Frequent exceedances of national daily PM limit have been reported in this city during the last decade, yet, the chemical composition and sources of fine particles are poorly determined. In the present study, 24-hour PM samples were collected at two urban sites during two separate campaigns, a one-year period from 2014 to 2015 and another three-month period at the beginning of 2017. Concentrations of organic carbon (OC), elemental carbon (EC), inorganic ions, trace metals and specific organic molecular markers were measured by chemical analysis of filter samples. The dominant mass components were organic matter (OM), sulfate and EC. With a 20% water-soluble organic carbon (WSOC) fraction, the predominance of primary anthropogenic sources (i.e. fossil fuel combustion) was anticipated. A positive matrix factorization (PMF) analysis using the ME-2 (Multilinear Engine-2) solver was then applied to this dataset. 5 factors were identified by Marker-PMF, named as traffic exhaust (TE), biomass burning (BB), industries (Ind.), nitrate-rich and sulfate-rich. Another 4 factors were identified by Metal-PMF, including, dust, vehicles (traffic non-exhaust, TNE), industries (Ind.) and heavy fuel combustion (HFC). Traffic exhaust was the dominant source with 44.5% contribution to total quantified PM mass. Sulfate-rich (24.2%) and nitrate-rich (18.4%) factors were the next major contributing sources. Dust (4.4%) and biomass burning (6.7%) also had small contributions while the total share of all other factors was < 2%. Investigating the correlations of different factors between the two sampling sites showed that traffic emissions and biomass burning were local, whereas dust, heavy fuel combustion and industrial sources were regional. Results of this study indicate that gas- and particle-phase pollutants emitted from fossil fuel combustion (mobile and stationary) are the principal origin of both primary and secondary fine aerosols in Tehran.
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http://dx.doi.org/10.1016/j.scitotenv.2019.135330DOI Listing
February 2020

Real-Time Detection of Aerosol Metals Using Online Extractive Electrospray Ionization Mass Spectrometry.

Anal Chem 2020 01 26;92(1):1316-1325. Epub 2019 Dec 26.

Engineering (ENAC) , École Polytechnique Fédérale de Lausanne (EPFL) , CH 1015 Lausanne , Switzerland.

Metal emissions are of major environmental and practical concern because of their highly toxic effects on human health and ecosystems. Current technologies available in the market for their detection are typically limited by a time resolution of 1 h or longer (e.g., via semicontinuous X-ray fluorescence measurements) or are nonquantitative (e.g., laser ablation mass spectrometry). In this work, we report the development of a novel technique for the real-time detection and monitoring of metal particles in situ using an extractive electrospray ionization (EESI) source coupled to a high-resolution time-of-flight mass spectrometer (TOF-MS). The experiments were conducted in negative ionization mode using disodium ethylenediamine tetraacetic acid (EDTA) dihydrate to chelate with metals and form stable metal complexes. Results for water-soluble metal compounds were obtained. The following representative metal ions were examined: Pb, Cd, Zn, Ce (III), Ba, Ni, Fe(II), Fe(III), Cu(II), Cr, Mo, Co(II), Mg, Nd, Li, Ti, Ca, Cs, Ag, Tm, Er(III), La(III), Yb(III), Eu(III), Pr(III), Gd(III), Lu(III), Dy(III), Tb(III), Ho, and Ru(III). The results showed a very good linear mass response ( = 0.9983), low ng/m limits of detection (LoD), and a fast response time (1 s). The stability and repeatability of the developed EESI-TOF-MS were tested under complex dynamic and periodic experimental conditions, and negligible matrix effects were measured for internally and externally mixed metal particles. Benchmark testing against inductively coupled plasma-mass spectrometry (ICP-MS) was also performed, highlighting the online measurement capabilities of aerosol metals with a LoD lower than those of ICP-MS. Proof-of-concept ambient measurements were performed in New Delhi, India, and very promising results were obtained, allowing further exploitation elsewhere.
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http://dx.doi.org/10.1021/acs.analchem.9b04480DOI Listing
January 2020

A Comprehensive Nontarget Analysis for the Molecular Reconstruction of Organic Aerosol Composition from Glacier Ice Cores.

Environ Sci Technol 2019 Nov 14;53(21):12565-12575. Epub 2019 Oct 14.

Bioenergy and Catalysis Laboratory , Paul Scherrer Institute , 5232 Villigen , Switzerland.

Ice cores are climate archives suitable for the reconstruction of past atmospheric composition changes. Ice core analysis provides valuable insight into the chemical nature of aerosols and enables constraining emission inventories of primary emissions and of gas-phase precursors. Changes in the emissions of volatile organic compounds (VOCs) can affect formation rates and mechanisms as well as chemical composition of aerosols during the preindustrial era, key information for understanding aerosol climate effects. Here, we present an analytical method for the reconstruction of organic aerosol composition preserved in glacier ice cores. A solid-phase-extraction method, optimized toward oxidation products of biogenic VOCs, provides an enrichment factor of ∼200 and quantitative recovery for compounds of interest. We applied the preconcentration method on ice core samples from the high-alpine Fiescherhorn glacier (Swiss Alps), and used high-performance liquid chromatography coupled to high-resolution mass spectrometry as a sensitive detection method. We describe a nontarget analysis that screens for organic molecules in the ice core samples. We evaluate the atmospheric origin of the detected compounds in the ice by molecular-resolved comparison with airborne particulate matter samples from the nearby high-alpine research station Jungfraujoch. The presented method is able to shed light upon the history of the evolution of organic aerosol composition in the anthropocene, a research field in paleoclimatology with considerable potential.
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http://dx.doi.org/10.1021/acs.est.9b03091DOI Listing
November 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.

Department of Applied Physics , University of Eastern Finland , PO Box 1627, 70211 Kuopio , Finland.

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

Quantification of the impact of cooking processes on indoor concentrations of volatile organic species and primary and secondary organic aerosols.

Indoor Air 2019 11 17;29(6):926-942. Epub 2019 Sep 17.

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland.

Cooking is recognized as an important source of particulate pollution in indoor and outdoor environments. We conducted more than 100 individual experiments to characterize the particulate and non-methane organic gas emissions from various cooking processes, their reaction rates, and their secondary organic aerosol yields. We used this emission data to develop a box model, for simulating the cooking emission concentrations in a typical European home and the indoor gas-phase reactions leading to secondary organic aerosol production. Our results suggest that about half of the indoor primary organic aerosol emission rates can be explained by cooking. Emission rates of larger and unsaturated aldehydes likely are dominated by cooking while the emission rates of terpenes are negligible. We found that cooking dominates the particulate and gas-phase air pollution in non-smoking European households exceeding 1000 μg m . While frying processes are the main driver of aldehyde emissions, terpenes are mostly emitted due to the use of condiments. The secondary aerosol production is negligible with around 2 μg m . Our results further show that ambient cooking organic aerosol concentrations can only be explained by super-polluters like restaurants. The model offers a comprehensive framework for identifying the main parameters controlling indoor gas- and particle-phase concentrations.
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http://dx.doi.org/10.1111/ina.12597DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6856830PMC
November 2019

A global view on the effect of water uptake on aerosol particle light scattering.

Sci Data 2019 08 22;6(1):157. Epub 2019 Aug 22.

Department of Environmental Science and Analytical Chemistry, Stockholm University, SE-10691, Stockholm, Sweden.

A reference dataset of multi-wavelength particle light scattering and hemispheric backscattering coefficients for different relative humidities (RH) between RH = 30 and 95% and wavelengths between λ = 450 nm and 700 nm is described in this work. Tandem-humidified nephelometer measurements from 26 ground-based sites around the globe, covering multiple aerosol types, have been re-analysed and harmonized into a single dataset. The dataset includes multi-annual measurements from long-term monitoring sites as well as short-term field campaign data. The result is a unique collection of RH-dependent aerosol light scattering properties, presented as a function of size cut. This dataset is important for climate and atmospheric model-measurement inter-comparisons, as a means to improve model performance, and may be useful for satellite and remote sensing evaluation using surface-based, in-situ measurements.
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http://dx.doi.org/10.1038/s41597-019-0158-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6706437PMC
August 2019

Effect of Stove Technology and Combustion Conditions on Gas and Particulate Emissions from Residential Biomass Combustion.

Environ Sci Technol 2019 02 1;53(4):2209-2219. Epub 2019 Feb 1.

Laboratory of Atmospheric Chemistry , Paul Scherrer Institute , 5232 Villigen , Switzerland.

We have systematically examined the gas and particle phase emissions from seven wood combustion devices. Among total carbon mass emitted (excluding CO), CO emissions were dominant, together with nonmethane volatile organic compounds (NMVOCs) (10-40%). Automated devices emitted 1-3 orders of magnitude lower CH (0.002-0.60 g kg of wood) and NMVOCs (0.01-1 g kg of wood) compared to batch-operated devices (CH: 0.25-2.80 g kg of wood; NMVOCs: 2.5-19 g kg of wood). 60-90% of the total NMVOCs were emitted in the starting phase of batch-operated devices, except for the first load cycles. Partial-load conditions or deviations from the normal recommended operating conditions, such as use of wet wood/wheat pellets, oxygen rich or deficit conditions, significantly enhanced the emissions. NMVOCs were largely dominated by small carboxylic acids and alcohols, and furans. Despite the large variability in NMVOCs emission strengths, the relative contribution of different classes showed large similarities among different devices and combustion phases. We show that specific improper operating conditions may even for advanced technology not result in the emission reduction of secondary organic aerosol (SOA) forming compounds and thus not reduce the impact of wood combustion on climate and health.
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http://dx.doi.org/10.1021/acs.est.8b05020DOI Listing
February 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

Mitigation of Secondary Organic Aerosol Formation from Log Wood Burning Emissions by Catalytic Removal of Aromatic Hydrocarbons.

Environ Sci Technol 2018 11 5;52(22):13381-13390. Epub 2018 Nov 5.

Paul Scherrer Institute , Laboratory of Atmospheric Chemistry , 5232 Villigen , Switzerland.

Log wood burning is a significant source of volatile organic compounds including aromatic hydrocarbons (ArHC). ArHC are harmful, are reactive in the ambient atmosphere, and are important secondary organic aerosol (SOA) precursors. Consequently, SOA represents a major fraction of the sub-micron organic aerosol pollution from log wood burning. ArHC reduction is thus critical in the mitigation of adverse health and environmental effects of log wood burning. In this study, two Pt-based catalytic converters were prepared and tested for the mitigation of real-world log wood burning emissions, including ArHC and SOA formation, as well as toxic carbon monoxide and methane, a greenhouse gas. Substantial removal of mono- and polycyclic ArHC and phenolic compounds was achieved with both catalysts operated at realistic chimney temperatures (50% conversion was achieved at 200 and 300 °C for non-methane hydrocarbons in our experiments for Pt/AlO and Pt/CeO-AlO respectively). The catalytically cleaned emissions exhibited a substantially reduced SOA formation already at temperatures as low as 185-310 °C. This reduces the sub-micron PM burden of log wood burning significantly. Thus, catalytic converters can effectively reduce primary and secondary log wood burning pollutants and, thereby, their adverse health impacts and environmental effects.
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http://dx.doi.org/10.1021/acs.est.8b04124DOI Listing
November 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.

Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany.

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

Characterization of Gas-Phase Organics Using Proton Transfer Reaction Time-of-Flight Mass Spectrometry: Residential Coal Combustion.

Environ Sci Technol 2018 03 13;52(5):2612-2617. Epub 2018 Feb 13.

Laboratory of Atmospheric Chemistry , Paul Scherrer Institute , Villigen , 5232 , Switzerland.

Residential coal combustion is a significant contributor to particulate urban air pollution in Chinese mega cities and some regions in Europe. While the particulate emission factors and the chemical characteristics of the organic and inorganic aerosol from coal combustion have been extensively studied, the chemical composition and nonmethane organic gas (NMOG) emission factors from residential coal combustion are mostly unknown. We conducted 23 individual burns in a traditional Chinese stove used for heating and cooking using five different coals with Chinese origins, characterizing the NMOG emissions using a proton transfer reaction time-of-flight mass spectrometer. The measured emission factors range from 1.5 to 14.1 g/kg for bituminous coals and are below 0.1 g/kg for anthracite coals. The emission factors from the bituminous coals are mostly influenced by the time until the coal is fully ignited. The emissions from the bituminous coals are dominated by aromatic and oxygenated aromatic compounds with a significant contribution of hydrocarbons. The results of this study can help to improve urban air pollution modeling in China and Eastern Europe and can be used to constrain a coal burning factor in ambient gas phase positive matrix factorization studies.
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http://dx.doi.org/10.1021/acs.est.7b03960DOI Listing
March 2018