scholarly journals Effects of anthropogenic emissions on aerosol formation from isoprene and monoterpenes in the southeastern United States

2014 ◽  
Vol 112 (1) ◽  
pp. 37-42 ◽  
Author(s):  
Lu Xu ◽  
Hongyu Guo ◽  
Christopher M. Boyd ◽  
Mitchel Klein ◽  
Aikaterini Bougiatioti ◽  
...  
Keyword(s):  
United States ◽  
Particulate Matter ◽  
Fine Particulate Matter ◽  
Southeastern United States ◽  
Organic Aerosol ◽  
High Time Resolution ◽  
Organic Nitrates ◽  
Aerosol Formation ◽  
Radical Oxidation ◽  
Southeastern Us

Secondary organic aerosol (SOA) constitutes a substantial fraction of fine particulate matter and has important impacts on climate and human health. The extent to which human activities alter SOA formation from biogenic emissions in the atmosphere is largely undetermined. Here, we present direct observational evidence on the magnitude of anthropogenic influence on biogenic SOA formation based on comprehensive ambient measurements in the southeastern United States (US). Multiple high-time-resolution mass spectrometry organic aerosol measurements were made during different seasons at various locations, including urban and rural sites in the greater Atlanta area and Centreville in rural Alabama. Our results provide a quantitative understanding of the roles of anthropogenic SO2 and NOx in ambient SOA formation. We show that isoprene-derived SOA is directly mediated by the abundance of sulfate, instead of the particle water content and/or particle acidity as suggested by prior laboratory studies. Anthropogenic NOx is shown to enhance nighttime SOA formation via nitrate radical oxidation of monoterpenes, resulting in the formation of condensable organic nitrates. Together, anthropogenic sulfate and NOx can mediate 43–70% of total measured organic aerosol (29–49% of submicron particulate matter, PM1) in the southeastern US during summer. These measurements imply that future reduction in SO2 and NOx emissions can considerably reduce the SOA burden in the southeastern US. Updating current modeling frameworks with these observational constraints will also lead to more accurate treatment of aerosol formation for regions with substantial anthropogenic−biogenic interactions and consequently improve air quality and climate simulations.

scholarly journals In situ vertical profiles of aerosol extinction, mass, and composition over the southeast United States during SENEX and SEAC<sup>4</sup>RS: observations of a modest aerosol enhancement aloft

2015 ◽  
Vol 15 (3) ◽  
pp. 3127-3172 ◽  
Author(s):  
N. L. Wagner ◽  
C. A. Brock ◽  
W. M. Angevine ◽  
A. Beyersdorf ◽  
P. Campuzano-Jost ◽  
...  
Keyword(s):  
United States ◽  
Mixed Layer ◽  
Transition Layer ◽  
Southeastern United States ◽  
Vertical Mixing ◽  
Organic Aerosol ◽  
Vertical Profiles ◽  
Free Troposphere ◽  
Aerosol Formation

Abstract. Vertical profiles of submicron aerosol over the southeastern United States (SEUS) during the summertime from in situ aircraft-based measurements were used to construct aggregate profiles of chemical, microphysical, and optical properties. Shallow cumulus convection was observed during many profiles. These conditions enhance vertical transport of trace gases and aerosol and create a cloudy transition layer on top of the sub-cloud mixed layer. The trace gas and aerosol concentrations in the transition layer were modeled as a mixture with contributions from the mixed layer below and the free troposphere above. The amount of vertical mixing, or entrainment of air from the free troposphere, was quantified using the observed mixing ratio of carbon monoxide (CO). Although the median aerosol mass, extinction, and volume decreased with altitude in the transition layer, they were ~10% larger than expected from vertical mixing alone. This enhancement was likely due to secondary aerosol formation in the transition layer. Although the transition layer enhancements of the particulate sulfate and organic aerosol (OA) were both similar in magnitude, only the enhancement of sulfate was statistically significant. The column integrated extinction, or aerosol optical depth (AOD), was calculated for each individual profile, and the transition layer enhancement of extinction typically contributed less than 10% to the total AOD. Our measurements and analysis were motivated by two recent studies that have hypothesized an enhanced layer of secondary organic aerosol (SOA) aloft to explain the summertime enhancement of AOD (2–3 times greater than winter) over the southeastern United States. In contrast to this hypothesis, the modest enhancement we observed in the transition layer was not dominated by OA and was not a large fraction of the summertime AOD.

scholarly journals Aerosol optical properties in the southeastern United States in summer – Part 1: Hygroscopic growth

2016 ◽  
Vol 16 (8) ◽  
pp. 4987-5007 ◽  
Author(s):  
Charles A. Brock ◽  
Nicholas L. Wagner ◽  
Bruce E. Anderson ◽  
Alexis R. Attwood ◽  
Andreas Beyersdorf ◽  
...  
Keyword(s):  
United States ◽  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Layer Structure ◽  
Southeastern United States ◽  
Organic Aerosol ◽  
Hygroscopic Growth ◽  
Aerosol Composition ◽  
Optical Extinction ◽  
Southeastern Us

Abstract. Aircraft observations of meteorological, trace gas, and aerosol properties were made during May–September 2013 in the southeastern United States (US) under fair-weather, afternoon conditions with well-defined planetary boundary layer structure. Optical extinction at 532 nm was directly measured at relative humidities (RHs) of  ∼  15,  ∼  70, and  ∼  90 % and compared with extinction calculated from measurements of aerosol composition and size distribution using the κ-Köhler approximation for hygroscopic growth. The calculated enhancement in hydrated aerosol extinction with relative humidity, f(RH), calculated by this method agreed well with the observed f(RH) at  ∼  90 % RH. The dominance of organic aerosol, which comprised 65 ± 10 % of particulate matter with aerodynamic diameter  <  1 µm in the planetary boundary layer, resulted in relatively low f(RH) values of 1.43 ± 0.67 at 70 % RH and 2.28 ± 1.05 at 90 % RH. The subsaturated κ-Köhler hygroscopicity parameter κ for the organic fraction of the aerosol must have been  <  0.10 to be consistent with 75 % of the observations within uncertainties, with a best estimate of κ  =  0.05. This subsaturated κ value for the organic aerosol in the southeastern US is broadly consistent with field studies in rural environments. A new, physically based, single-parameter representation was developed that better described f(RH) than did the widely used gamma power-law approximation.

scholarly journals Aerosol loading in the Southeastern United States: reconciling surface and satellite observations

2013 ◽  
Vol 13 (18) ◽  
pp. 9269-9283 ◽  
Author(s):  
B. Ford ◽  
C. L. Heald
Keyword(s):  
United States ◽  
Fine Particulate Matter ◽  
Southeastern United States ◽  
Vertical Mixing ◽  
Lower Troposphere ◽  
Organic Aerosol ◽  
Surface Mass ◽  
Fine Particulate ◽  
Surface Network ◽  
Surface Observations

Abstract. We investigate the seasonality in aerosols over the Southeastern United States using observations from several satellite instruments (MODIS, MISR, CALIOP) and surface network sites (IMPROVE, SEARCH, AERONET). We find that the strong summertime enhancement in satellite-observed aerosol optical depth (AOD) (factor 2–3 enhancement over wintertime AOD) is not present in surface mass concentrations (25–55% summertime enhancement). Goldstein et al. (2009) previously attributed this seasonality in AOD to biogenic organic aerosol; however, surface observations show that organic aerosol only accounts for ∼35% of fine particulate matter (smaller than 2.5 μm in aerodynamic diameter, PM2.5) and exhibits similar seasonality to total surface PM2.5. The GEOS-Chem model generally reproduces these surface aerosol measurements, but underrepresents the AOD seasonality observed by satellites. We show that seasonal differences in water uptake cannot sufficiently explain the magnitude of AOD increase. As CALIOP profiles indicate the presence of additional aerosol in the lower troposphere (below 700 hPa), which cannot be explained by vertical mixing, we conclude that the discrepancy is due to a missing source of aerosols above the surface layer in summer.

Quantifying the sources of ozone, fine particulate matter, and regional haze in the Southeastern United States

2009 ◽  
Vol 90 (10) ◽  
pp. 3155-3168 ◽  
Author(s):  
M. Talat Odman ◽  
Yongtao Hu ◽  
Armistead G. Russell ◽  
Asude Hanedar ◽  
James W. Boylan ◽  
...  
Keyword(s):  
United States ◽  
Particulate Matter ◽  
Fine Particulate Matter ◽  
Southeastern United States ◽  
Fine Particulate ◽  
Regional Haze
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