Secondary organic aerosol (SOA) yields from NO<sub>3</sub> radical + isoprene based on nighttime aircraft power plant plume transects

Abstract

Abstract. Nighttime reaction of nitrate radicals (NO 3 ) with biogenic volatile organic compounds (BVOC) has been proposed as a potentially important but also highly uncertain source of secondary organic aerosol (SOA). The southeastern United States has both high BVOC and nitrogen oxide (NO x ) emissions, resulting in a large model-predicted NO 3 -BVOC source of SOA. Coal-fired power plants in this region constitute substantial NO x emissions point sources into a nighttime atmosphere characterized by high regionally widespread concentrations of isoprene. In this paper, we exploit nighttime aircraft observations of these power plant plumes, in which NO 3 radicals rapidly remove isoprene, to obtain field-based estimates of the secondary organic aerosol yield from NO 3 + isoprene. Observed in-plume increases in nitrate aerosol are consistent with organic nitrate aerosol production from NO 3 + isoprene, and these are used to determine molar SOA yields, for which the average over nine plumes is 9 % (±5 %). Corresponding mass yields depend on the assumed molecular formula for isoprene-NO 3 -SOA, but the average over nine plumes is 27 % (±14 %), on average larger than those previously measured in chamber studies (12 %-14 % mass yield as OA / VOC after oxidation of both double bonds). Yields are larger for longer plume ages. This suggests that ambient aging processes lead more effectively to condensable material than typical chamber conditions allow. We discuss potential mechanistic explanations for this difference, including longer ambient peroxy radical lifetimes and heterogeneous reactions of NO 3 -isoprene gas phase products. More in-depth studies are needed to better understand the aerosol yield and oxidation mechanism of NO 3 radical + isoprene, a coupled anthropogenic-biogenic source of SOA that may be regionally significant.

Efficient Nighttime Biogenic SOA Formation in a Polluted Residual Layer

“…While the exact mechanisms responsible for the formation of low volatility organic nitrates still remains to be understood, we found that the overall efficiency of nighttime biogenic SOA formation, as characterized by the ΔOA/ΔCO ratio, was about 100 μg m −3 ppmv, which falls in the range 77-157 μg m −3 ppmv previously estimated for enhanced daytime SOA formation from mixed anthropogenic and biogenic emissions during CARES (Shilling et al, 2013). Using a box model to calculate the amounts of isoprene reacted, we estimated SOA mass yields ranging from 0 to 0.55, which are a factor of 5 to 10 higher than measured in chamber studies (Ng et al, 2008;Rollins et al, 2009) but consistent with the mass yields estimated from field measurements (Fry et al, 2018). Further research is needed to fully elucidate the dominant NO 3 oxidation pathways so they can be represented in atmospheric aerosol models to reliably predict nighttime SOA formation from anthropogenic-biogenic interactions in a larger realm.…”

“…The figure also shows the estimated overall SOA mass yields calculated by dividing the observed SOA masses by the corresponding modeled amounts of total isoprene mass reacted. The overall yields range from 0 to 0.35 and are consistent with those estimated for nighttime isoprene SOA formation from field measurements by Fry et al (2018).…”

“…As NO 3 concentration depends on the availability of NO x , a substantial fraction of the biogenic SOA formed at night is controlled by anthropogenic emissions, as has been observed and predicted in several regions across the United States, Europe, and China (Ayres et al, 2015;Brown et al, 2013;Fry et al, 2018;Kiendler-Scharr et al, 2016;Pye et al, 2015;Rollins et al, 2012;Yu et al, 2019;Zaveri et al, 2010). We report here on nighttime biogenic SOA formation in a polluted residual layer over Sacramento, California, during the Carbonaceous Aerosols and Radiative Effects Study (CARES) in June 2010 (Zaveri et al, 2012).…”

Chemical Composition and Hydrolysis of Organic Nitrate Aerosol Formed from Hydroxyl and Nitrate Radical Oxidation of α-pinene and β-pinene

“…For the majority of nitrate-containing aerosol regardless of the class (i.e., inorganic or organic), the nitrate moiety (i.e., -NO2, -ONO2, and -O2NO2) was known to be thermally fragmented into NO + and NO2 + and was measured as NO3 (Farmer et al, 2010). As many past studies have demonstrated the feasibility to separate the contribution of inorganic (NO3,Inorg) and organic nitrate (NO3,Org) to the measured NO3 based on the ratio of NO + and NO2 + (Fry et al, 2009;Farmer et al, 2010;Xu et al, 2015b;Kiendler-Scharr et al, 2016;Fry et al, 2018), we used Eq. (1) presented in Farmer et al (2010) to obtain NO3,Org.…”

Rates of Wintertime Atmospheric SO2 Oxidation based on Aircraft Observations during Clear‐Sky Conditions over the Eastern United States

“…Journal of Geophysical Research: Atmospheres indicate that nighttime power plant plumes were widespread horizontally but confined vertically, transporting as fanning plumes (Brown et al, 2012;Fibiger et al, 2018;Fry et al, 2018;Stull, 1988). The profiles also show the SO 2 plumes were situated just above the onset of a steeper gradient in potential temperature that indicates the nocturnal boundary layer.…”