Recent advances in understanding secondary organic aerosol: Implications for global climate forcing

Abstract

Anthropogenic emissions and land use changes have modified atmospheric aerosol concentrations and size distributions over time. Understanding preindustrial conditions and changes in organic aerosol due to anthropogenic activities is important because these features (1) influence estimates of aerosol radiative forcing and (2) can confound estimates of the historical response of climate to increases in greenhouse gases. Secondary organic aerosol (SOA), formed in the atmosphere by oxidation of organic gases, represents a major fraction of global submicron‐sized atmospheric organic aerosol. Over the past decade, significant advances in understanding SOA properties and formation mechanisms have occurred through measurements, yet current climate models typically do not comprehensively include all important processes. This review summarizes some of the important developments during the past decade in understanding SOA formation. We highlight the importance of some processes that influence the growth of SOA particles to sizes relevant for clouds and radiative forcing, including formation of extremely low volatility organics in the gas phase, acid‐catalyzed multiphase chemistry of isoprene epoxydiols, particle‐phase oligomerization, and physical properties such as volatility and viscosity. Several SOA processes highlighted in this review are complex and interdependent and have nonlinear effects on the properties, formation, and evolution of SOA. Current global models neglect this complexity and nonlinearity and thus are less likely to accurately predict the climate forcing of SOA and project future climate sensitivity to greenhouse gases. Efforts are also needed to rank the most influential processes and nonlinear process‐related interactions, so that these processes can be accurately represented in atmospheric chemistry‐climate models.

Urban influence on the concentration and composition of submicron particulate matter in central Amazonia

“…A metastudy for several locations in the USA concluded that air downwind of urban areas had increased organic PM concentrations due to the photochemical production of SOM (De Gouw and Jimenez, 2009). Models have estimated that 50 % to 70 % of the biogenic SOM mass concentration in several locations is modulated by anthropogenic emissions (Carlton et al, 2010;Heald et al, 2011;Spracklen et al, 2011). In addition, global-scale modeling studies have estimated an increase of 20 % to 60 % in the global annual mean SOM concentration relative to the preindustrial period (Tsigaridis et al, 2006;Hoyle et al, 2009).…”

Aircraft-based observations of isoprene epoxydiol-derived secondary organic aerosol (IEPOX-SOA) in the tropical upper troposphere over the Amazon region

“…Volatile organic compounds (VOCs) emitted by vegetation can lead to the formation of secondary organic aerosol (SOA) 10 through atmospheric oxidation and further chemical processes (e.g., Zhang et al, 2007;Jimenez et al, 2009;Hallquist et al, 2009;Shrivastava et al, 2017). One important VOC is isoprene (C 5 H 8 , 2-methyl-1,3-butadiene), the most abundant nonmethane hydrocarbon with a global emission rate of~500 Tg y −1 , with a large contribution coming from the Amazon rain forest (Guenther et al, 2012).…”

“…Oxidation of VOCs with the highly reactive nitrate radical NO 3 can lead to different nitrogen-containing oxidation products that can partition to the aerosol-phase (e.g., Kroll and Seinfeld, 2008;Shrivastava et al, 2017). The nitrate radical oxidation of 15 VOCs can contribute up to 20 % of the global VOC oxidation and is supposed to increase the aerosol mass significantly .…”

“…Many studies reported on the difficulties to measure organic 10 nitrates quantitatively, but suggested also a possibility to estimate the amount or at least the presence of organic nitrates based on the measured ion ratios of NO + to NO + 2 using aerosol mass spectrometry (e.g., Bruns et al, 2010;Farmer et al, 2010;Rollins et al, 2010;Fry et al, 2013;Ayres et al, 2015;Kiendler-Scharr et al, 2016;Ng et al, 2017;Schneider et al, 2017).…”

Aircraft Observations of Aerosol in the Manaus Urban Plume and Surrounding Tropical Forest during GoAmazon 2014/15

“…Several additional 20 field studies report enhancements of SOA through interactions of anthropogenic and biogenic interactions, but may not employ the Δorg/ΔCO metric (Zhou et al, 2016;Xu et al, 2015;Ng et al, 2017;Bean et al, 2016). The potential mechanisms responsible for these enhancements are known in some cases but remain uncertain in others and have been outlined in recent review articles Ng et al, 2017;Glasius and Goldstein, 2016;Hoyle et al, 2011).…”