Browsing by Author "Wernis, Rebecca A."
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- Contributions of biomass-burning, urban, and biogenic emissions to the concentrations and light-absorbing properties of particulate matter in central Amazonia during the dry seasonde Sa, Suzane S.; Rizzo, Luciana V.; Palm, Brett B.; Campuzano-Jost, Pedro; Day, Douglas A.; Yee, Lindsay D.; Wernis, Rebecca A.; Isaacman-VanWertz, Gabriel; Brito, Joel; Carbone, Samara; Liu, Yingjun J.; Sedlacek, Arthur; Springston, Stephen R.; Goldstein, Allen H.; Barbosa, Henrique M. J.; Alexander, M. Lizabeth; Artaxo, Paulo; Jimenez, Jose L.; Martin, Scot T. (European Geophysical Union, 2019-06-18)Urbanization and deforestation have important impacts on atmospheric particulate matter (PM) over Amazonia. This study presents observations and analysis of PM1 concentration, composition, and optical properties in central Amazonia during the dry season, focusing on the anthropogenic impacts. The primary study site was located 70 km downwind of Manaus, a city of over 2 million people in Brazil, as part of the GoAmazon2014/5 experiment. A high-resolution time-of-flight aerosol mass spectrometer (AMS) provided data on PM1 composition, and aethalometer measurements were used to derive the absorption coefficient b(abs,BrC) of brown carbon (BrC) at 370 nm. Non-refractory PM1 mass concentrations averaged 12.2 mu g m(-3) at the primary study site, dominated by organics (83 %), followed by sulfate (11 %). A decrease in b(abs,BrC) was observed as the mass concentration of nitrogen-containing organic compounds decreased and the organic PM1 O : C ratio increased, suggesting atmospheric bleaching of the BrC components. The organic PM1 was separated into six different classes by positive-matrix factorization (PMF), and the mass absorption efficiency E-abs associated with each factor was estimated through multivariate linear regression of b(abs,BrC) on the factor loadings. The largest E-abs values were associated with urban (2.04 +/- 0.14 m(2) g(-1)) and biomass-burning (0.82 +/- 0.04 to 1.50 +/- 0.07 m(2)g(-1)) sources. Together, these sources contributed at least 80 % of b(abs,BrC) while accounting for 30 % to 40 % of the organic PM1 mass concentration. In addition, a comparison of organic PM1 composition between wet and dry seasons revealed that only part of the 9-fold increase in mass concentration between the seasons can be attributed to biomass burning. Biomass-burning factor loadings increased by 30-fold, elevating its relative contribution to organic PM1 from about 10 % in the wet season to 30 % in the dry season. However, most of the PM1 mass (> 60 %) in both seasons was accounted for by biogenic secondary organic sources, which in turn showed an 8-fold seasonal increase in factor loadings. A combination of decreased wet deposition and increased emissions and oxidant concentrations, as well as a positive feedback on larger mass concentrations are thought to play a role in the observed increases. Furthermore, fuzzy c-means clustering identified three clusters, namely "baseline", "event", and "urban" to represent different pollution influences during the dry season. The baseline cluster, representing the dry season background, was associated with a mean mass concentration of 9 +/- 3 mu g m(-3). This concentration increased on average by 3 mu g m(-3) for both the urban and the event clusters. The event cluster, representing an increased influence of biomass burning and long-range transport of African volcanic emissions, was characterized by remarkably high sulfate concentrations. The urban cluster, representing the influence of Manaus emissions on top of the baseline, was characterized by an organic PM1 composition that differed from the other two clusters. The differences discussed suggest a shift in oxidation pathways as well as an accelerated oxidation cycle due to urban emissions, in agreement with findings for the wet season.
- Emissions of organic compounds from western US wildfires and their near-fire transformationsLiang, Yutong; Stamatis, Christos; Fortner, Edward C.; Wernis, Rebecca A.; Van Rooy, Paul; Majluf, Francesca; Yacovitch, Tara, I; Daube, Conner; Herndon, Scott C.; Kreisberg, Nathan M.; Barsanti, Kelley C.; Goldstein, Allen H. (Copernicus, 2022-08-03)The size and frequency of wildfires in the western United States have been increasing, and this trend is projected to continue, with increasing adverse consequences for human health. Gas- and particle-phase organic compounds are the main components of wildfire emissions. Some of the directly emitted compounds are hazardous air pollutants, while others can react with oxidants to form secondary air pollutants such as ozone and secondary organic aerosol (SOA). Further, compounds emitted in the particle phase can volatize during smoke transport and can then serve as precursors for SOA. The extent of pollutant formation from wildfire emissions is dependent in part on the speciation of organic compounds. The most detailed speciation of organic compounds has been achieved in laboratory studies, though recent field campaigns are leading to an increase in such measurements in the field. In this study, we identified and quantified hundreds of gas- and particle-phase organic compounds emitted from conifer-dominated wildfires in the western US, using two two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC x GC ToF-MS) instruments. Observed emission factors (EFs) and emission ratios are reported for four wildfires. As has been demonstrated previously, modified combustion efficiency (MCE) was a good predictor of particle-phase EFs (e.g., R-2=0.78 and 0.84 for sugars and terpenoids, respectively), except for elemental carbon. Higher emissions of diterpenoids, resin acids, and monoterpenes were observed in the field relative to laboratory studies, likely due to distillation from unburned heated vegetation, which may be underrepresented in laboratory studies. These diterpenoids and resin acids accounted for up to 45 % of total quantified organic aerosol, higher than the contribution from sugar and sugar derivatives. The low volatility of resin acids makes them ideal markers for conifer fire smoke. The speciated measurements also show that evaporation of semi-volatile organic compounds took place in smoke plumes, which suggests that the evaporated primary organic aerosol can be a precursor of SOAs in wildfire smoke plumes.
- Observations of sesquiterpenes and their oxidation products in central Amazonia during the wet and dry seasonsYee, Lindsay D.; Isaacman-VanWertz, Gabriel; Wernis, Rebecca A.; Meng, Meng; Rivera, Ventura; Kreisberg, Nathan M.; Hering, Susanne V.; Bering, Mads S.; Glasius, Marianne; Upshur, Mary Alice; Be, Ariana Gray; Thomson, Regan J.; Geiger, Franz M.; Offenberg, John H.; Lewandowski, Michael; Kourtchev, Ivan; Kalberer, Markus; de Sa, Suzane S.; Martin, Scot T.; Alexander, M. Lizabeth; Palm, Brett B.; Hu, Weiwei; Campuzano-Jost, Pedro; Day, Douglas A.; Jimenez, Jose L.; Liu, Yingjun; McKinney, Karena A.; Artaxo, Paulo; Viegas, Juarez; Manzi, Antonio; Oliveira, Maria B.; de Souza, Rodrigo; Machado, Luiz A. T.; Longo, Karla; Goldstein, Allen H. (European Geophysical Union, 2018-07-23)Biogenic volatile organic compounds (BVOCs) from the Amazon forest region represent the largest source of organic carbon emissions to the atmosphere globally. These BVOC emissions dominantly consist of volatile and intermediate-volatility terpenoid compounds that undergo chemical transformations in the atmosphere to form oxygenated condensable gases and secondary organic aerosol (SOA). We collected quartz filter samples with 12 h time resolution and performed hourly in situ measurements with a semi-volatile thermal desorption aerosol gas chromatograph (SV-TAG) at a rural site ("T3") located to the west of the urban center of Manaus, Brazil as part of the Green Ocean Amazon (GoAmazon2014/5) field campaign to measure intermediate-volatility and semi-volatile BVOCs and their oxidation products during the wet and dry seasons. We speciated and quantified 30 sesquiterpenes and 4 diterpenes with mean concentrations in the range 0.01-6.04 ng m(-3) (1670 ppq(v)). We estimate that sesquiterpenes contribute approximately 14 and 12% to the total reactive loss of O-3 via reaction with isoprene or terpenes during the wet and dry seasons, respectively. This is reduced from similar to 50-70% for within-canopy reactive O-3 loss attributed to the ozonolysis of highly reactive sesquiterpenes (e.g., beta-caryophyllene) that are reacted away before reaching our measurement site. We further identify a suite of their oxidation products in the gas and particle phases and explore their role in biogenic SOA formation in the central Amazon region. Synthesized authentic standards were also used to quantify gas-and particle-phase oxidation products derived from beta-caryophyllene. Using tracer-based scaling methods for these products, we roughly estimate that sesquiterpene oxidation contributes at least 0.4-5% (median 1 %) of total submicron OA mass. However, this is likely a low-end estimate, as evidence for additional unaccounted sesquiterpenes and their oxidation products clearly exists. By comparing our field data to laboratory-based sesquiterpene oxidation experiments we confirm that more than 40 additional observed compounds produced through sesquiterpene oxidation are present in Amazonian SOA, warranting further efforts towards more complete quantification.
- Secondary organic aerosol formation from ambient air in an oxidation flow reactor in central AmazoniaPalm, Brett B.; de Sa, Suzane S.; Day, Douglas A.; Campuzano-Jost, Pedro; Hu, Weiwei; Seco, Roger; Sjostedt, Steven J.; Park, Jeong-Hoo; Guenther, Alex B.; Kim, Saewung; Brito, Joel; Wurm, Florian; Artaxo, Paulo; Thalman, Ryan; Wang, Jian; Yee, Lindsay D.; Wernis, Rebecca A.; Isaacman-VanWertz, Gabriel; Goldstein, Allen H.; Liu, Yingjun; Springston, Stephen R.; Souza, Rodrigo; Newburn, Matt K.; Alexander, M. Lizabeth; Martin, Scot T.; Jimenez, Jose L. (European Geophysical Union, 2018-01-17)Secondary organic aerosol (SOA) formation from ambient air was studied using an oxidation flow reactor (OFR) coupled to an aerosol mass spectrometer (AMS) during both the wet and dry seasons at the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) field campaign. Measurements were made at two sites downwind of the city of Manaus, Brazil. Ambient air was oxidized in the OFR using variable concentrations of either OH or O-3, over ranges from hours to days (O-3) or weeks (OH) of equivalent atmospheric aging. The amount of SOA formed in the OFR ranged from 0 to as much as 10 mu g m(-3), depending on the amount of SOA precursor gases in ambient air. Typically, more SOA was formed during nighttime than daytime, and more from OH than from O-3 oxidation. SOA yields of individual organic precursors under OFR conditions were measured by standard addition into ambient air and were confirmed to be consistent with published environmental chamber-derived SOA yields. Positive matrix factorization of organic aerosol (OA) after OH oxidation showed formation of typical oxidized OA factors and a loss of primary OA factors as OH aging increased. After OH oxidation in the OFR, the hygroscopicity of the OA increased with increasing elemental O : C up to O : C similar to 1.0, and then decreased as O : C increased further. Possible reasons for this decrease are discussed. The measured SOA formation was compared to the amount predicted from the concentrations of measured ambient SOA precursors and their SOA yields. While measured ambient precursors were sufficient to explain the amount of SOA formed from O-3, they could only explain 10-50% of the SOA formed from OH. This is consistent with previous OFR studies, which showed that typically unmeasured semivolatile and intermediate volatility gases (that tend to lack C=C bonds) are present in ambient air and can explain such additional SOA formation. To investigate the sources of the unmeasured SOA-forming gases during this campaign, multilinear regression analysis was performed between measured SOA formation and the concentration of gas-phase tracers representing different precursor sources. The majority of SOA-forming gases present during both seasons were of biogenic origin. Urban sources also contributed substantially in both seasons, while biomass burning sources were more important during the dry season. This study enables a better understanding of SOA formation in environments with diverse emission sources.