Light-absorbing soluble organic aerosol in Los Angeles and Atlanta: A contrast in secondary organic aerosol

Abstract

[1] Light absorption spectra and carbon mass of fine particle water-soluble components were measured during the summer of 2010 in the Los Angeles (LA) basin, California, and Atlanta, Georgia. Fresh LA secondary organic carbon had a consistent brown color and a bulk absorption per soluble carbon mass at 365 nm that was 4 to 6 times higher than freshly-formed Atlanta soluble organic carbon. Radiocarbon measurements of filter samples show that LA secondary organic aerosol (SOA) was mainly from fossil carbon and chemical analysis of aqueous filter extracts identified nitroaromatics as one component of LA brown SOA. Interpreting soluble brown carbon as a property of freshly-formed anthropogenic SOA, the difference in absorption per carbon mass between these two cities suggests most fresh secondary water-soluble organic carbon formed within Atlanta is not from an anthropogenic process similar to LA. Contrasting emissions of biogenic volatile organic compounds may account for these differences. Citation:

Joint measurements of PM<sub>2. 5</sub> and light-absorptive PM in woodsmoke-dominated ambient and plume environments

“…This comparison further supports DC as a qualitative woodsmoke marker. As mentioned earlier, previous studies found that SOA products may result in DC signals (Zhang et al, 2011;Zhong and Jang, 2011). If SOA formation were significant, we would expect that PM 2.5 and/or DC would peak around mid-day.…”

Gasoline emissions dominate over diesel in formation of secondary organic aerosol mass

“…Considering that BC was <15% of the TC mass (Figure 2d), TC closely represents OC during CalNex. In addition, the afternoon increase in TC mass is predominantly due to the increase in the fossil fraction, suggesting that photooxidation of anthropogenic organic compounds is the major contributor to SOA within the city plume [Zhang et al, 2011].…”

Biogenic, urban, and wildfire influences on the molecular composition of dissolved organic compounds in cloud water

“…A higher absolute number and number fraction of CHNO compounds were observed during the wildfire and urban air mass periods, compared to biogenic influence, likely due to greater NO x influence. In addition, observations of likely dinitroaromatics during all air mass influences, potentially from aqueous nitration of nitroaromatic compounds, have important implications because of their light-absorbing and mutagenic properties (Purohit and Basu, 2000;Zhang et al, 2011Zhang et al, , 2013. During wildfire influence, the cloud water showed evidence of aqueous SOA formation, including oligomer formation involving methylglyoxal Yasmeen et al, 2010) and aqueousphase reactions of syringol and guaiacol (Yu et al, 2014(Yu et al, , 2016.…”