Publications by authors named "Lynn M Russell"

27 Publications

  • Page 1 of 1

Factors driving the seasonal and hourly variability of sea-spray aerosol number in the North Atlantic.

Proc Natl Acad Sci U S A 2019 10 23;116(41):20309-20314. Epub 2019 Sep 23.

Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331.

Four North Atlantic Aerosol and Marine Ecosystems Study (NAAMES) field campaigns from winter 2015 through spring 2018 sampled an extensive set of oceanographic and atmospheric parameters during the annual phytoplankton bloom cycle. This unique dataset provides four seasons of open-ocean observations of wind speed, sea surface temperature (SST), seawater particle attenuation at 660 nm (, a measure of ocean particulate organic carbon), bacterial production rates, and sea-spray aerosol size distributions and number concentrations (). The NAAMES measurements show moderate to strong correlations (0.56 < < 0.70) between and local wind speeds in the marine boundary layer on hourly timescales, but this relationship weakens in the campaign averages that represent each season, in part because of the reduction in range of wind speed by multiday averaging. correlates weakly with seawater c ( = 0.36, < 0.01), but the correlation with c, is improved ( = 0.51, < 0.05) for periods of low wind speeds. In addition, NAAMES measurements provide observational dependence of SSA mode diameter () on SST, with increasing to larger sizes at higher SST ( = 0.60, < 0.01) on hourly timescales. These results imply that climate models using bimodal SSA parameterizations to wind speed rather than a single SSA mode that varies with SST may overestimate SSA number concentrations (hence cloud condensation nuclei) by a factor of 4 to 7 and may underestimate SSA scattering (hence direct radiative effects) by a factor of 2 to 5, in addition to overpredicting variability in SSA scattering from wind speed by a factor of 5.
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http://dx.doi.org/10.1073/pnas.1907574116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6789830PMC
October 2019

Influences of Primary Emission and Secondary Coating Formation on the Particle Diversity and Mixing State of Black Carbon Particles.

Environ Sci Technol 2019 Aug 2;53(16):9429-9438. Epub 2019 Aug 2.

Department of Civil and Environmental Engineering , University of California , Davis , California 95616 , United States.

The mixing state of black carbon (BC) affects its environmental fate and impacts. This work investigates particle diversity and mixing state for refractory BC (rBC) containing particles in an urban environment. The chemical compositions of individual rBC-containing particles were measured, from which a mixing state index and particle diversity were determined. The mixing state index (χ) varied between 26% and 69% with the average of 48% in this study and was slightly enhanced with the photochemical age of air masses, indicating that most of the rBC-containing particles cannot be simply explained by fully externally and internally mixed model. Clustering of single particle measurements was used to investigate the potential effects of different primary emissions and atmospheric processes on rBC-containing particle diversity and mixing state. The average particle species diversity and the bulk population species diversity both increased with primary traffic emissions and elevated nitrate concentrations in the morning but gradually decreased with secondary organic aerosol (SOA) formation in the afternoon. The single particle clustering results illustrate that primary traffic emissions and entrainment of nitrate-containing rBC particles from the residual layer to the surface could lead to more heterogeneous aerosol compositions, whereas substantial fresh SOA formation near vehicular emissions made the rBC-containing particles more homogeneous. This work highlights the importance of considering particle diversity and mixing state for investigating the chemical evolution of rBC-containing particles and the potential effects of coating on BC absorption enhancement.
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http://dx.doi.org/10.1021/acs.est.9b03064DOI Listing
August 2019

Substantial Seasonal Contribution of Observed Biogenic Sulfate Particles to Cloud Condensation Nuclei.

Sci Rep 2018 02 19;8(1):3235. Epub 2018 Feb 19.

The Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, USA.

Biogenic sources contribute to cloud condensation nuclei (CCN) in the clean marine atmosphere, but few measurements exist to constrain climate model simulations of their importance. The chemical composition of individual atmospheric aerosol particles showed two types of sulfate-containing particles in clean marine air masses in addition to mass-based Estimated Salt particles. Both types of sulfate particles lack combustion tracers and correlate, for some conditions, to atmospheric or seawater dimethyl sulfide (DMS) concentrations, which means their source was largely biogenic. The first type is identified as New Sulfate because their large sulfate mass fraction (63% sulfate) and association with entrainment conditions means they could have formed by nucleation in the free troposphere. The second type is Added Sulfate particles (38% sulfate), because they are preexisting particles onto which additional sulfate condensed. New Sulfate particles accounted for 31% (7 cm) and 33% (36 cm) CCN at 0.1% supersaturation in late-autumn and late-spring, respectively, whereas sea spray provided 55% (13 cm) in late-autumn but only 4% (4 cm) in late-spring. Our results show a clear seasonal difference in the marine CCN budget, which illustrates how important phytoplankton-produced DMS emissions are for CCN in the North Atlantic.
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http://dx.doi.org/10.1038/s41598-018-21590-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5818515PMC
February 2018

Regional Similarities and NO-related Increases in Biogenic Secondary Organic Aerosol in Summertime Southeastern U.S.

J Geophys Res Atmos 2018 ;123(18):10620-10636

Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.

During the 2013 Southern Oxidant and Aerosol Study, Fourier Transform Infrared Spectroscopy (FTIR) and Aerosol Mass Spectrometer (AMS) measurements of submicron mass were collected at Look Rock (LRK), Tennessee, and Centreville (CTR), Alabama. Carbon monoxide and submicron sulfate and organic mass concentrations were 15-60% higher at CTR than at LRK but their time series had moderate correlations (r~0.5). However, NO had no correlation (r=0.08) between the two sites with nighttime-to-early-morning peaks 3~10 times higher at CTR than at LRK. Organic mass (OM) sources identified by FTIR Positive Matrix Factorization (PMF) had three very similar factors at both sites: Fossil Fuel Combustion (FFC) related organic aerosols, Mixed Organic Aerosols (MOA), and Biogenic Organic Aerosols (BOA). The BOA spectrum from FTIR is similar (cosine similarity > 0.6) to that of lab-generated particle mass from the photochemical oxidation of both isoprene and monoterpenes under high NO conditions from chamber experiments. The BOA mass fraction was highest during the night at CTR but in the afternoon at LRK. AMS PMF resulted in two similar pairs of factors at both sites and a third nighttime NO-related factor (33% of OM) at CTR but a daytime nitrate-related factor (28% of OM) at LRK. NO was correlated with BOA and LO-OOA for NO concentrations higher than 1 ppb at both sites, producing 0.5 ± 0.1 μg m for CTR-LO-OOA and 1.0 ± 0.3 μg m for CTR-BOA above 1 ppb additional biogenic OM for each 1 ppb increase of NO.
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http://dx.doi.org/10.1029/2018JD028491DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6463306PMC
January 2018

January 2016 extensive summer melt in West Antarctica favoured by strong El Niño.

Nat Commun 2017 06 15;8:15799. Epub 2017 Jun 15.

Byrd Polar and Climate Research Center, The Ohio State University, 1090 Carmack Road, Columbus, Ohio 43210, USA.

Over the past two decades the primary driver of mass loss from the West Antarctic Ice Sheet (WAIS) has been warm ocean water underneath coastal ice shelves, not a warmer atmosphere. Yet, surface melt occurs sporadically over low-lying areas of the WAIS and is not fully understood. Here we report on an episode of extensive and prolonged surface melting observed in the Ross Sea sector of the WAIS in January 2016. A comprehensive cloud and radiation experiment at the WAIS ice divide, downwind of the melt region, provided detailed insight into the physical processes at play during the event. The unusual extent and duration of the melting are linked to strong and sustained advection of warm marine air toward the area, likely favoured by the concurrent strong El Niño event. The increase in the number of extreme El Niño events projected for the twenty-first century could expose the WAIS to more frequent major melt events.
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http://dx.doi.org/10.1038/ncomms15799DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5481731PMC
June 2017

Dust-wind interactions can intensify aerosol pollution over eastern China.

Nat Commun 2017 05 11;8:15333. Epub 2017 May 11.

Atmospheric Science and Global Change Division, Pacific Northwest National Laboratory, Richland, Washington 99354, USA.

Eastern China has experienced severe and persistent winter haze episodes in recent years due to intensification of aerosol pollution. In addition to anthropogenic emissions, the winter aerosol pollution over eastern China is associated with unusual meteorological conditions, including weaker wind speeds. Here we show, based on model simulations, that during years with decreased wind speed, large decreases in dust emissions (29%) moderate the wintertime land-sea surface air temperature difference and further decrease winds by -0.06 (±0.05) m s averaged over eastern China. The dust-induced lower winds enhance stagnation of air and account for about 13% of increasing aerosol concentrations over eastern China. Although recent increases in anthropogenic emissions are the main factor causing haze over eastern China, we conclude that natural emissions also exert a significant influence on the increases in wintertime aerosol concentrations, with important implications that need to be taken into account by air quality studies.
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http://dx.doi.org/10.1038/ncomms15333DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5437281PMC
May 2017

Comparison of Gasoline Direct-Injection (GDI) and Port Fuel Injection (PFI) Vehicle Emissions: Emission Certification Standards, Cold-Start, Secondary Organic Aerosol Formation Potential, and Potential Climate Impacts.

Environ Sci Technol 2017 Jun 9;51(11):6542-6552. Epub 2017 May 9.

Department of Mechanical Engineering, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States.

Recent increases in the Corporate Average Fuel Economy standards have led to widespread adoption of vehicles equipped with gasoline direct-injection (GDI) engines. Changes in engine technologies can alter emissions. To quantify these effects, we measured gas- and particle-phase emissions from 82 light-duty gasoline vehicles recruited from the California in-use fleet tested on a chassis dynamometer using the cold-start unified cycle. The fleet included 15 GDI vehicles, including 8 GDIs certified to the most-stringent emissions standard, superultra-low-emission vehicles (SULEV). We quantified the effects of engine technology, emission certification standards, and cold-start on emissions. For vehicles certified to the same emissions standard, there is no statistical difference of regulated gas-phase pollutant emissions between PFIs and GDIs. However, GDIs had, on average, a factor of 2 higher particulate matter (PM) mass emissions than PFIs due to higher elemental carbon (EC) emissions. SULEV certified GDIs have a factor of 2 lower PM mass emissions than GDIs certified as ultralow-emission vehicles (3.0 ± 1.1 versus 6.3 ± 1.1 mg/mi), suggesting improvements in engine design and calibration. Comprehensive organic speciation revealed no statistically significant differences in the composition of the volatile organic compounds emissions between PFI and GDIs, including benzene, toluene, ethylbenzene, and xylenes (BTEX). Therefore, the secondary organic aerosol and ozone formation potential of the exhaust does not depend on engine technology. Cold-start contributes a larger fraction of the total unified cycle emissions for vehicles meeting more-stringent emission standards. Organic gas emissions were the most sensitive to cold-start compared to the other pollutants tested here. There were no statistically significant differences in the effects of cold-start on GDIs and PFIs. For our test fleet, the measured 14.5% decrease in CO emissions from GDIs was much greater than the potential climate forcing associated with higher black carbon emissions. Thus, switching from PFI to GDI vehicles will likely lead to a reduction in net global warming.
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http://dx.doi.org/10.1021/acs.est.6b06509DOI Listing
June 2017

Semivolatile POA and parameterized total combustion SOA in CMAQv5.2: impacts on source strength and partitioning.

Atmos Chem Phys 2017 ;17:11107-11133

National Exposure Research Laboratory, US Environmental Protection Agency, Research Triangle Park, NC, USA.

Mounting evidence from field and laboratory observations coupled with atmospheric model analyses shows that primary combustion emissions of organic compounds dynamically partition between the vapor and particulate phases, especially as near-source emissions dilute and cool to ambient conditions. The most recent version of the Community Multiscale Air Quality model version 5.2 (CMAQv5.2) accounts for the semivolatile partitioning and gas-phase aging of these primary organic aerosol (POA) compounds consistent with experimentally derived parameterizations. We also include a new surrogate species, potential secondary organic aerosol from combustion emissions (pcSOA), which provides a representation of the secondary organic aerosol (SOA) from anthropogenic combustion sources that could be missing from current chemical transport model predictions. The reasons for this missing mass likely include the following: (1) unspeciated semivolatile and intermediate volatility organic compound (SVOC and IVOC, respectively) emissions missing from current inventories, (2) multigenerational aging of organic vapor products from known SOA precursors (e.g., toluene, alkanes), (3) underestimation of SOA yields due to vapor wall losses in smog chamber experiments, and (4) reversible organic compounds-water interactions and/or aqueous-phase processing of known organic vapor emissions. CMAQ predicts the spatially averaged contribution of pcSOA to OA surface concentrations in the continental United States to be 38.6 and 23.6 % in the 2011 winter and summer, respectively. Whereas many past modeling studies focused on a particular measurement campaign, season, location, or model configuration, we endeavor to evaluate the model and important uncertain parameters with a comprehensive set of United States-based model runs using multiple horizontal scales (4 and 12 km), gas-phase chemical mechanisms, and seasons and years. The model with representation of semivolatile POA improves predictions of hourly OA observations over the traditional nonvolatile model at sites during field campaigns in southern California (CalNex, May-June 2010), northern California (CARES, June 2010), the southeast US (SOAS, June 2013; SEARCH, January and July, 2011). Model improvements manifest better correlations (e.g., the correlation coefficient at Pasadena at night increases from 0.38 to 0.62) and reductions in underprediction during the photochemically active afternoon period (e.g., bias at Pasadena from -5.62 to -2.42 μg m). Daily averaged predictions of observations at routine-monitoring networks from simulations over the continental US (CONUS) in 2011 show modest improvement during winter, with mean biases reducing from 1.14 to 0.73μg m, but less change in the summer when the decreases from POA evaporation were similar to the magnitude of added SOA mass. Because the model-performance improvement realized by including the relatively simple pcSOA approach is similar to that of more-complicated parameterizations of OA formation and aging, we recommend caution when applying these more-complicated approaches as they currently rely on numerous uncertain parameters. The pcSOA parameters optimized for performance at the southern and northern California sites lead to higher OA formation than is observed in the CONUS evaluation. This may be due to any of the following: variations in real pcSOA in different regions or time periods, too-high concentrations of other OA sources in the model that are important over the larger domain, or other model issues such as loss processes. This discrepancy is likely regionally and temporally dependent and driven by interferences from factors like varying emissions and chemical regimes.
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http://dx.doi.org/10.5194/acp-17-11107-2017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7006837PMC
January 2017

Atmospheric science: Sea-spray particles cause freezing in clouds.

Authors:
Lynn M Russell

Nature 2015 Sep;525(7568):194-5

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093-0221, USA.

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http://dx.doi.org/10.1038/525194aDOI Listing
September 2015

Observational insights into aerosol formation from isoprene.

Environ Sci Technol 2013 Oct 3;47(20):11403-13. Epub 2013 Oct 3.

Department of Environmental Science, Policy and Management, ∥Department of Chemistry, University of California , Berkeley, California 94720, United States.

Atmospheric photooxidation of isoprene is an important source of secondary organic aerosol (SOA) and there is increasing evidence that anthropogenic oxidant emissions can enhance this SOA formation. In this work, we use ambient observations of organosulfates formed from isoprene epoxydiols (IEPOX) and methacrylic acid epoxide (MAE) and a broad suite of chemical measurements to investigate the relative importance of nitrogen oxide (NO/NO2) and hydroperoxyl (HO2) SOA formation pathways from isoprene at a forested site in California. In contrast to IEPOX, the calculated production rate of MAE was observed to be independent of temperature. This is the result of the very fast thermolysis of MPAN at high temperatures that affects the distribution of the MPAN reservoir (MPAN / MPA radical) reducing the fraction that can react with OH to form MAE and subsequently SOA (F(MAE formation)). The strong temperature dependence of F(MAE formation) helps to explain our observations of similar concentrations of IEPOX-derived organosulfates (IEPOX-OS; ~1 ng m(-3)) and MAE-derived organosulfates (MAE-OS; ~1 ng m(-3)) under cooler conditions (lower isoprene concentrations) and much higher IEPOX-OS (~20 ng m(-3)) relative to MAE-OS (<0.0005 ng m(-3)) at higher temperatures (higher isoprene concentrations). A kinetic model of IEPOX and MAE loss showed that MAE forms 10-100 times more ring-opening products than IEPOX and that both are strongly dependent on aerosol water content when aerosol pH is constant. However, the higher fraction of MAE ring opening products does not compensate for the lower MAE production under warmer conditions (higher isoprene concentrations) resulting in lower formation of MAE-derived products relative to IEPOX at the surface. In regions of high NOx, high isoprene emissions and strong vertical mixing the slower MPAN thermolysis rate aloft could increase the fraction of MPAN that forms MAE resulting in a vertically varying isoprene SOA source.
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http://dx.doi.org/10.1021/es4011064DOI Listing
October 2013

Bringing the ocean into the laboratory to probe the chemical complexity of sea spray aerosol.

Proc Natl Acad Sci U S A 2013 May 25;110(19):7550-5. Epub 2013 Apr 25.

Department of Chemistry and Biochemistry and Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093, USA.

The production, size, and chemical composition of sea spray aerosol (SSA) particles strongly depend on seawater chemistry, which is controlled by physical, chemical, and biological processes. Despite decades of studies in marine environments, a direct relationship has yet to be established between ocean biology and the physicochemical properties of SSA. The ability to establish such relationships is hindered by the fact that SSA measurements are typically dominated by overwhelming background aerosol concentrations even in remote marine environments. Herein, we describe a newly developed approach for reproducing the chemical complexity of SSA in a laboratory setting, comprising a unique ocean-atmosphere facility equipped with actual breaking waves. A mesocosm experiment was performed in natural seawater, using controlled phytoplankton and heterotrophic bacteria concentrations, which showed SSA size and chemical mixing state are acutely sensitive to the aerosol production mechanism, as well as to the type of biological species present. The largest reduction in the hygroscopicity of SSA occurred as heterotrophic bacteria concentrations increased, whereas phytoplankton and chlorophyll-a concentrations decreased, directly corresponding to a change in mixing state in the smallest (60-180 nm) size range. Using this newly developed approach to generate realistic SSA, systematic studies can now be performed to advance our fundamental understanding of the impact of ocean biology on SSA chemical mixing state, heterogeneous reactivity, and the resulting climate-relevant properties.
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http://dx.doi.org/10.1073/pnas.1300262110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3651460PMC
May 2013

Insights into secondary organic aerosol formation mechanisms from measured gas/particle partitioning of specific organic tracer compounds.

Environ Sci Technol 2013 Apr 27;47(8):3781-7. Epub 2013 Mar 27.

Department of Environmental Science, Policy and Management, University of California, Berkeley, California, USA.

In situ measurements of organic compounds in both gas and particle phases were made with a thermal desorption aerosol gas chromatography (TAG) instrument. The gas/particle partitioning of phthalic acid, pinonaldehyde, and 6,10,14-trimethyl-2-pentadecanone is discussed in detail to explore secondary organic aerosol (SOA) formation mechanisms. Measured fractions in the particle phase (f(part)) of 6,10,14-trimethyl-2-pentadecanone were similar to those expected from the absorptive gas/particle partitioning theory, suggesting that its partitioning is dominated by absorption processes. However, f(part) of phthalic acid and pinonaldehyde were substantially higher than predicted. The formation of low-volatility products from reactions of phthalic acid with ammonia is proposed as one possible mechanism to explain the high f(part) of phthalic acid. The observations of particle-phase pinonaldehyde when inorganic acids were fully neutralized indicate that inorganic acids are not required for the occurrence of reactive uptake of pinonaldehyde on particles. The observed relationship between f(part) of pinonaldehyde and relative humidity suggests that the aerosol water plays a significant role in the formation of particle-phase pinonaldehyde. Our results clearly show it is necessary to include multiple gas/particle partitioning pathways in models to predict SOA and multiple SOA tracers in source apportionment models to reconstruct SOA.
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http://dx.doi.org/10.1021/es304587xDOI Listing
April 2013

Removal of sea salt hydrate water from seawater-derived samples by dehydration.

Environ Sci Technol 2012 Dec 3;46(24):13326-33. Epub 2012 Dec 3.

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA.

Aerosol particles produced from bubble bursting of natural seawater contain both sea salts and organic components. Depending on the temperature, pressure, and speed of drying, the salt components can form hydrates that bind water, slowing evaporation of the water, particularly if large particles or thick layers of salts undergo drying that is nonuniform and incomplete. The water bound in these salt hydrates interferes with measuring organic hydroxyl and amine functional groups by Fourier transform infrared (FTIR) spectroscopy because it absorbs at the same infrared wavelengths. Here, a method for separating the hydrate water in sea salt hydrates using freezing and then heating in warm, dry air (70 °C) is evaluated and compared to other methods, including spectral subtraction. Laboratory-generated sea salt analogs show an efficient removal of 89% of the hydrate water absorption peak height by 24 h of heating at atmospheric pressure. The heating method was also applied to bubbled submicrometer (Sea Sweep), generated bulk (Bubbler), and atomized seawater samples, with efficient removal of 5, 22, and 39 μg of hydrate water from samples of initial masses of 11, 30, 58 μg, respectively. The strong spectral similarity between the difference of the initial and dehydrated spectra and the laboratory-generated sea salt hydrate spectrum provided verification of the removal of hydrate water. In contrast, samples of submicrometer atmospheric particles from marine air masses did not have detectable signatures of sea salt hydrate absorbance, likely because their smaller particles and lower filter loadings provided higher surface area to volume ratios and allowed faster and more complete drying.
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http://dx.doi.org/10.1021/es3032083DOI Listing
December 2012

Characterizing the aging of biomass burning organic aerosol by use of mixing ratios: a meta-analysis of four regions.

Environ Sci Technol 2012 Dec 30;46(24):13093-102. Epub 2012 Nov 30.

Centre for Atmospheric Science, School of Earth, Atmospheric and Environmental Science, University of Manchester, Manchester, United Kingdom.

Characteristic organic aerosol (OA) emission ratios (ERs) and normalized excess mixing ratios (NEMRs) for biomass burning (BB) events have been calculated from ambient measurements recorded during four field campaigns. Normalized OA mass concentrations measured using Aerodyne Research Inc. quadrupole aerosol mass spectrometers (Q-AMS) reveal a systematic variation in average values between different geographical regions. For each region, a consistent, characteristic ratio is seemingly established when measurements are collated from plumes of all ages and origins. However, there is evidence of strong regional and local-scale variability between separate measurement periods throughout the tropical, subtropical, and boreal environments studied. ERs close to source typically exceed NEMRs in the far-field, despite apparent compositional change and increasing oxidation with age. The absence of any significant downwind mass enhancement suggests no regional net source of secondary organic aerosol (SOA) from atmospheric aging of BB sources, in contrast with the substantial levels of net SOA formation associated with urban sources. A consistent trend of moderately reduced ΔOA/ΔCO ratios with aging indicates a small net loss of OA, likely as a result of the evaporation of organic material from initial fire emissions. Variability in ERs close to source is shown to substantially exceed the magnitude of any changes between fresh and aged OA, emphasizing the importance of fuel and combustion conditions in determining OA loadings from biomass burning.
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http://dx.doi.org/10.1021/es302386vDOI Listing
December 2012

Elucidating secondary organic aerosol from diesel and gasoline vehicles through detailed characterization of organic carbon emissions.

Proc Natl Acad Sci U S A 2012 Nov 22;109(45):18318-23. Epub 2012 Oct 22.

Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA.

Emissions from gasoline and diesel vehicles are predominant anthropogenic sources of reactive gas-phase organic carbon and key precursors to secondary organic aerosol (SOA) in urban areas. Their relative importance for aerosol formation is a controversial issue with implications for air quality control policy and public health. We characterize the chemical composition, mass distribution, and organic aerosol formation potential of emissions from gasoline and diesel vehicles, and find diesel exhaust is seven times more efficient at forming aerosol than gasoline exhaust. However, both sources are important for air quality; depending on a region's fuel use, diesel is responsible for 65% to 90% of vehicular-derived SOA, with substantial contributions from aromatic and aliphatic hydrocarbons. Including these insights on source characterization and SOA formation will improve regional pollution control policies, fuel regulations, and methodologies for future measurement, laboratory, and modeling studies.
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http://dx.doi.org/10.1073/pnas.1212272109DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3494959PMC
November 2012

Organic constituents on the surfaces of aerosol particles from Southern Finland, Amazonia, and California studied by vibrational sum frequency generation.

J Phys Chem A 2012 Aug 23;116(32):8271-90. Epub 2012 Jul 23.

Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.

This article summarizes and compares the analysis of the surfaces of natural aerosol particles from three different forest environments by vibrational sum frequency generation. The experiments were carried out directly on filter and impactor substrates, without the need for sample preconcentration, manipulation, or destruction. We discuss the important first steps leading to secondary organic aerosol (SOA) particle nucleation and growth from terpene oxidation by showing that, as viewed by coherent vibrational spectroscopy, the chemical composition of the surface region of aerosol particles having sizes of 1 μm and lower appears to be close to size-invariant. We also discuss the concept of molecular chirality as a chemical marker that could be useful for quantifying how chemical constituents in the SOA gas phase and the SOA particle phase are related in time. Finally, we describe how the combination of multiple disciplines, such as aerosol science, advanced vibrational spectroscopy, meteorology, and chemistry can be highly informative when studying particles collected during atmospheric chemistry field campaigns, such as those carried out during HUMPPA-COPEC-2010, AMAZE-08, or BEARPEX-2009, and when they are compared to results from synthetic model systems such as particles from the Harvard Environmental Chamber (HEC). Discussions regarding the future of SOA chemical analysis approaches are given in the context of providing a path toward detailed spectroscopic assignments of SOA particle precursors and constituents and to fast-forward, in terms of mechanistic studies, through the SOA particle formation process.
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http://dx.doi.org/10.1021/jp302631zDOI Listing
August 2012

Ecosystem impacts of geoengineering: a review for developing a science plan.

Ambio 2012 Jun 20;41(4):350-69. Epub 2012 Mar 20.

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0221, USA.

Geoengineering methods are intended to reduce climate change, which is already having demonstrable effects on ecosystem structure and functioning in some regions. Two types of geoengineering activities that have been proposed are: carbon dioxide (CO(2)) removal (CDR), which removes CO(2) from the atmosphere, and solar radiation management (SRM, or sunlight reflection methods), which reflects a small percentage of sunlight back into space to offset warming from greenhouse gases (GHGs). Current research suggests that SRM or CDR might diminish the impacts of climate change on ecosystems by reducing changes in temperature and precipitation. However, sudden cessation of SRM would exacerbate the climate effects on ecosystems, and some CDR might interfere with oceanic and terrestrial ecosystem processes. The many risks and uncertainties associated with these new kinds of purposeful perturbations to the Earth system are not well understood and require cautious and comprehensive research.
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http://dx.doi.org/10.1007/s13280-012-0258-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3393062PMC
June 2012

Identifying organic aerosol sources by comparing functional group composition in chamber and atmospheric particles.

Proc Natl Acad Sci U S A 2011 Mar 11;108(9):3516-21. Epub 2011 Feb 11.

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA.

Measurements of submicron particles by Fourier transform infrared spectroscopy in 14 campaigns in North America, Asia, South America, and Europe were used to identify characteristic organic functional group compositions of fuel combustion, terrestrial vegetation, and ocean bubble bursting sources, each of which often accounts for more than a third of organic mass (OM), and some of which is secondary organic aerosol (SOA) from gas-phase precursors. The majority of the OM consists of alkane, carboxylic acid, hydroxyl, and carbonyl groups. The organic functional groups formed from combustion and vegetation emissions are similar to the secondary products identified in chamber studies. The near absence of carbonyl groups in the observed SOA associated with combustion is consistent with alkane rather than aromatic precursors, and the absence of organonitrate groups can be explained by their hydrolysis in humid ambient conditions. The remote forest observations have ratios of carboxylic acid, organic hydroxyl, and nonacid carbonyl groups similar to those observed for isoprene and monoterpene chamber studies, but in biogenic aerosols transported downwind of urban areas the formation of esters replaces the acid and hydroxyl groups and leaves only nonacid carbonyl groups. The carbonyl groups in SOA associated with vegetation emissions provides striking evidence for the mechanism of esterification as the pathway for possible oligomerization reactions in the atmosphere. Forest fires include biogenic emissions that produce SOA with organic components similar to isoprene and monoterpene chamber studies, also resulting in nonacid carbonyl groups in SOA.
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http://dx.doi.org/10.1073/pnas.1006461108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3048156PMC
March 2011

Phenol groups in northeastern U.S. submicrometer aerosol particles produced from seawater sources.

Environ Sci Technol 2010 Apr;44(7):2542-8

Scripps Institution of Oceanography, University of California San Diego, La Jolla California 92093-0221, USA.

Atmospheric particles collected during the ICARTT 2004 field experiment at ground based sites at Appledore Island (AI), New Hampshire, Chebogue Point (CP), Nova Scotia, and aboard the R/V Ronald Brown (RB) were analyzed using Fourier transform infrared (FTIR) spectroscopy to quantify organic mass (OM) and organic functional groups. Several of these spectra contain a unique absorbance peak at 3500 cm(-1). Laboratory calibrations identify this peak with phenol functional groups. The phenol groups are associated with seawater-derived emissions based on correlations with tracer volatile organic compounds (VOCs) and ions, and potential source contribution function (PSCF) analysis. On the basis of the measured absorptivities, the project average phenol group concentrations are 0.24 +/- 0.18 microg m(-3) (4% of the total OM) at AI, 0.10 +/- 0.6 microg m(-3) (5% of the total OM) at CP, and 0.08 +/- 0.09 microg m(-3) (2% of the total OM) on board the RB, with detection limits typically between 0.06 and 0.11 microg m(-3). The spectra were partitioned into three primary factors using positive matrix factorization (PMF) sufficient to explain more than 95% of the measured OM. The fossil fuel combustion factor contributed 40% (AI), 34% (CP), and 43% (RB) of the total OM; the terrestrial biogenic factor contributed 20% (AI), 30% (CP), and 27% (RB). The seawater-derived factor contributed 40% (AI), 36% (CP) and 29% (RB) of the OM and showed similar correlations to tracers as the phenol group.
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http://dx.doi.org/10.1021/es9032277DOI Listing
April 2010

Carbohydrate-like composition of submicron atmospheric particles and their production from ocean bubble bursting.

Proc Natl Acad Sci U S A 2010 Apr 23;107(15):6652-7. Epub 2009 Dec 23.

Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093, USA.

Oceans cover over two-thirds of the Earth's surface, and the particles emitted to the atmosphere by waves breaking on sea surfaces provide an important contribution to the planetary albedo. During the International Chemistry Experiment in the Arctic LOwer Troposphere (ICEALOT) cruise on the R/V Knorr in March and April of 2008, organic mass accounted for 15-47% of the submicron particle mass in the air masses sampled over the North Atlantic and Arctic Oceans. A majority of this organic component (0.1-0.4 microm(-3)) consisted of organic hydroxyl (including polyol and other alcohol) groups characteristic of saccharides, similar to biogenic carbohydrates found in seawater. The large fraction of organic hydroxyl groups measured during ICEALOT in submicron atmospheric aerosol exceeded those measured in most previous campaigns but were similar to particles in marine air masses in the open ocean (Southeast Pacific Ocean) and coastal sites at northern Alaska (Barrow) and northeastern North America (Appledore Island and Chebogue Point). The ocean-derived organic hydroxyl mass concentration during ICEALOT correlated strongly to submicron Na concentration and wind speed. The observed submicron particle ratios of marine organic mass to Na were enriched by factors of approximately 10(2)-approximately 10(3) over reported sea surface organic to Na ratios, suggesting that the surface-controlled process of film bursting is influenced by the dissolved organic components present in the sea surface microlayer. Both marine organic components and Na increased with increasing number mean diameter of the accumulation mode, suggesting a possible link between organic components in the ocean surface and aerosol-cloud interactions.
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http://dx.doi.org/10.1073/pnas.0908905107DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2872374PMC
April 2010

Water uptake coefficients and deliquescence of NaCl nanoparticles at atmospheric relative humidities from molecular dynamics simulations.

J Chem Phys 2008 Sep;129(9):094508

Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0221, USA.

Deliquescence properties of sodium chloride are size dependent for particles smaller than 100 nm. Molecular dynamics (MD) simulations are used to determine deliquescence relative humidity (DRH) for particles in this size range by modeling idealized particles in contact with humid air. Constant humidity conditions are simulated by inclusion of a liquid reservoir of NaCl solution in contact with the vapor phase, which acts as a source of water molecules as uptake by the nanoparticle proceeds. DRH is bounded between the minimum humidity at which sustained water accumulation is observed at the particle surface and the maximum humidity at which water accumulation is not observed. Complete formation of a liquid layer is not observed due to computational limitations. The DRH determined increases with decreasing particle diameter, rising to between 91% and 93% for a 2.2 nm particle and between 81% and 85% for an 11 nm particle, higher than the 75% expected for particles larger than 100 nm. The simulated size dependence of DRH agrees well with predictions from bulk thermodynamic models and appears to converge with measurements for sizes larger than 10 nm. Complete deliquescence of nanoparticles in the 2-11 nm size range requires between 1 and 100 mus, exceeding the available computational resources for this study. Water uptake coefficients are near 0.1 with a negligible contribution from diffusion effects. Planar uptake coefficients decrease from 0.41 to 0.09 with increasing fractional water coverage from 0.002 to 1, showing a linear dependence on the logarithm of the coverage fraction with a slope of -0.08+/-0.01 (representing the effect of solvation). Particle uptake coefficients increase from 0.13 at 11 nm to 0.65 at 2.2 nm, showing a linear dependence on the logarithm of the edge fraction (which is a function of diameter) with a slope of 0.74+/-0.04 (representing larger edge effects in smaller particles).
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http://dx.doi.org/10.1063/1.2971040DOI Listing
September 2008

Surface tensions in NaCl-water-air systems from MD simulations.

J Phys Chem B 2007 Oct 26;111(41):11989-96. Epub 2007 Sep 26.

Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0221, USA.

Surface tensions for liquid-vapor (lv), solid-liquid (sl), and solid-vapor (sv) interfaces are calculated from molecular dynamics simulations of the NaCl-water-air system. Three distinct calculation techniques based on thermodynamic properties are used to describe the multicomponent mixtures. Simulations of each bulk phase (including a liquid saturated solution) and various interfaces are carried out at both NPT and NVT conditions. The thermodynamic relation for energy difference between interface and bulk phases provides an upper bound to the surface tension, while the energy-integral and test area methods provide direct estimates. At 1 atm and 300 K, the best predictions for surface tensions are sigmasv (NaCl-air) of 114 mN m(-1), sigmasl (NaCl- soln) of 63 mN m(-1), sigmalv (soln-air) of 82 mN m(-1), and sigmalv (water-air) of 66 mN m(-1). The calculated surface tensions from simulations have uncertainties between 5 and 10%, which are higher than measurements for the liquid interfaces and lower than the measurement uncertainty for the solid interfaces. The calculated upper bounds for surface tensions of liquid interfaces compare well with experimental results but provide no improvement over existing measurements. However, the bounding values for solid interfaces lower uncertainty by as much as a factor of 10 as compared to the indirect experimental measurements currently available. The energy-integral and test area methods appear to underestimate the surface tension of water by 10%, which is consistent with previous studies using similar model potentials. The calculated upper bounds of surface tension show a weakly positive correlation with pressure in the 0.1-100 atm range for liquid-solid, liquid-vapor, and solid-vapor interfaces.
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http://dx.doi.org/10.1021/jp075356cDOI Listing
October 2007

Void-induced dissolution in molecular dynamics simulations of NaCl and water.

J Chem Phys 2006 Apr;124(15):154713

Scripps Institution of Oceanography, University of California-San Diego, La Jolla, California 92093-0221, USA.

To gain a better understanding of the interaction of water and NaCl at the surface during dissolution, we have used molecular dynamics to simulate the interface with two equal-sized slabs of solid NaCl and liquid water in contact. The introduction of voids in the bulk of the salt, as well as steps or pits on the surface of the NaCl slab results in a qualitative change of system structure, as defined by radial distribution functions (RDFs). As an example, the characteristic Na-Na RDF for the system changes from regularly spaced narrow peaks (corresponding to an ordered crystalline structure), to a broad primary and smaller secondary peak (corresponding to a disordered structure). The change is observed at computationally short time scales of 100 ps, in contrast with a much longer time scale of 1 mus expected for complete mixing in the absence of defects. The void fraction (which combines both bulk and surface defects) required to trigger dissolution varies between 15%-20% at 300 K and 1 atm, and has distinct characteristics for the physical breakdown of the crystal lattice. The void fraction required decreases with temperature. Sensitivity studies show a strong dependence of the critical void fraction on the quantity and distribution of voids on the surface, with systems containing a balanced number of surface defects and a rough surface showing a maximum tendency to dissolve. There is a moderate dependence on temperature, with a 5% decrease in required void fraction with a 100 K increase in temperature, and a weak dependence on water potential model used, with the SPC, SPC/E, TIP4P, and RPOL models giving qualitatively identical results. The results were insensitive to the total quantity of water available for dissolution and the duration of the simulation.
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http://dx.doi.org/10.1063/1.2185091DOI Listing
April 2006

Organic and inorganic aerosol below-cloud scavenging by suburban New Jersey precipitation.

Environ Sci Technol 2005 Jul;39(13):4793-800

SciTec, Inc., Princeton, New Jersey 08540, USA.

Ambient aerosol size distributions and chemical composition in Princeton, NJ, were measured during a 10-day period in August 2003. Ten precipitation events during the sampling period maintained low aerosol concentrations, with an average gravimetric PM1.0 of 8.2 +/- 1.6 microg m(-3) and an average Fourier transform infrared (FTIR) spectroscopy-measured PM1.0 of 8.6 +/- 0.8 microg m(-3). A constrained factor analysis shows that the measured aerosol composition data are consistent with coal combustion and motor vehicle emissions. FTIR spectroscopy shows that the alkene fraction of organic mass (OM) was larger in the aerosol samples dominated by motor vehicle emissions than in the samples dominated by coal combustion, but the solvent-rinsing behavior was unaffected by source type. The aerosol OM was hydrophilic throughout the sampling period, with an average of 52% +/- 10% of the identified OM removed in the water-rinsing stage of the FTIR analysis. Measurements before and after rain events showed changes in particle composition and number distribution that were used to characterize the rate and chemical selectivity of particle removal processes associated with precipitation (or, in general terms, scavenging). The changes in ambient particle distributions showed an average PM1.0 below-cloud scavenging coefficient of 7 x 10(-5) +/- 3 x 10(-5) s(-1), with variability associated with chemical composition. The fraction of the aerosol OM removed in water rinses decreased during rain events, typically 55% at the start and 30% at the end of the observed rain events. These measured chemically dependent removal rates are consistent with other field measurements and can be used to improve the description of aerosol lifetimes in global models.
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http://dx.doi.org/10.1021/es0491679DOI Listing
July 2005

Organic aerosol growth mechanisms and their climate-forcing implications.

Science 2004 Dec;306(5703):1921-4

Department of Chemical Engineering, Princeton University, Princeton, NJ 08544, USA.

Surface- and volume-limited chemical reactions on and in atmospheric aerosol particles cause growth while changing organic composition by 13 to 24% per day. Many of these particles contain carbonaceous components from mineral dust and combustion emissions in Africa, Asia, and North America and reveal reaction rates that are three times slower than those typically used in climate models. These slower rates for converting from volatile or hydrophobic to condensed and hygroscopic organic compounds increase carbonaceous particle burdens in climate models by 70%, producing organic aerosol climate forcings of as much as -0.8 watt per square meter cooling and +0.3 watt per square meter warming.
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http://dx.doi.org/10.1126/science.1103491DOI Listing
December 2004

Aerosol organic-mass-to-organic-carbon ratio measurements.

Authors:
Lynn M Russell

Environ Sci Technol 2003 Jul;37(13):2982-7

Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08648, USA.

The ratio of organic-mass-to-organic-carbon, typically taken to be between 1.4 and 1.7, has an uncertainty higher than 50%, but this value is used in every measurement to date of the organic fraction of atmospheric particles. A recently developed technique with errors reduced to between 9% and 33% provides measurements of this ratio that show its large variability for samples measured in northeastern Asia and the Caribbean. The technique uses functional groups measured by FTIR spectroscopy to estimate composite organic carbon from the number of carbon bonds present and organic mass from the molecular mass of each functional group associated with the measured bond type. The molecular masses associated with each functional group are not unique and do not account for highly branched organic compositions. For the organic mixtures described by the less than 20% of atmospheric organic mass that has been speciated by GCMS, the theoretical discrepancy in the composite organic-mass-to-organic-carbon ratio is less than 5%. The measured ratios for submicron particle samples are skewed: over 90% of the measurements collected lie between 1.2 and 1.6, with mean values just below 1.4. This variability highlights the importance of measured organic-mass-to-organic-carbon ratios to reduce the uncertainty associated with atmospheric organic aerosol.
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http://dx.doi.org/10.1021/es026123wDOI Listing
July 2003