Particle partitioning potential of organic compounds is highest in the Eastern US and driven by anthropogenic water

Abstract

Gas-phase water-soluble organic matter (WSOM_g) is ubiquitous in the troposphere. In the summertime, the potential for these gases to partition to particle-phase liquid water (H₂O_ptcl) where they can form secondary organic aerosol (SOA_AQ) is high in the Eastern US and low elsewhere, with the exception of an area near Los Angeles, CA. This spatial pattern is driven by mass concentrations of H₂O_ptcl, not WSOM_g. H₂O_ptcl mass concentrations are predicted to be high in the Eastern US, largely due to sulfate. The ability of sulfate to increase H₂O_ptcl is well established and routinely included in atmospheric models; however WSOM_g partitioning to this water and subsequent SOA formation is not. The high mass concentrations of H₂O_ptcl in the southeast (SE) US but not the Amazon may help explain why biogenic SOA mass concentrations are high in the SE US but low in the Amazon. Furthermore, during the summertime in the Eastern US, the potential for organic gases to partition into liquid water is greater than their potential to partition into organic matter (OM) because concentrations of WSOM_g and H₂O_ptcl are higher than semi-volatile gases and OM. Thus, unless condensed phase yields are substantially different (> ~ order of magnitude), we expect that SOA formed through aqueous-phase pathways (SOA_AQ) will dominate in the Eastern US. These findings also suggest that H₂O_ptcl is largely anthropogenic and provide a previously unrecognized mechanism by which anthropogenic pollutants impact the amount of SOA mass formed from biogenic organic emissions. The previously reported estimate of the controllable fraction of biogenic SOA in the Eastern US (50%) is likely too low

Vertically resolved concentration and liquid water content of atmospheric nanoparticles at the US DOE Southern Great Plains site

“…Thus far, mechanisms of new particle growth such as salt formation (Barsanti et al, 2009;Smith et al, 2010;Hodshire et al, 2016), condensation of extremely low-volatility organic compounds (ELVOCs) Donahue et al, 2011;Riipinen et al, 2012;Jokinen et al, 2012;Ehn et al, 2014;Hodshire et al, 2016;Pierce et al, 2011), and reactive uptake of organics through particle-phase reactions such as aldol condensation (Jang et al, 2002;Limbeck et al, 2003;Barsanti and Pankow, 2004), have been identified. Many of these reactions in newly formed particles might be enhanced by high water content, which has been shown for submicron particles in many field, laboratory, and modeling studies (Blando and Turpin, 2000;Hennigan et al, 2008;Galloway et al, 2009;Ervens et al, 2011;Carlton and Turpin, 2013). In addition, the enhancing effect of water in NPF and growth was observed in the reaction of methanesulfonic acid and amines (Chen et al, 2015a, b).…”

Tropospheric sources and sinks of gas-phase acids in the Colorado Front Range

“…However, this was likely not a significant sink given the arid climate of the Front Range. Carlton and Turpin (2013) suggest that liquid water concentration in the Front Range during summer is ∼ 1 µg m −3 . Combining this with known constants, campaign mean mixing ratios, and meteorological conditions, aqueousphase partitioning accounts for an estimated loss of < 2 × 10 −10 ppb v of each alkanoic acid (see Supplement).…”

Semivolatile POA and parameterized total combustion SOA in CMAQv5.2: impacts on source strength and partitioning

“…Carlton and Turpin (2013), Pye et al (2013), and Pye et al (2017) argued that higher aerosol water concentrations, possibly resulting from increased sulfate concentrations in the past, could have enhanced the partitioning of semivolatile organic compounds, depending on their solubility, or they could have enhanced reactive uptake rates of VOC oxidation products. This is consistent with Xu et al (2017), who showed that 88 % of OA were water soluble at the Centreville site during SOAS and that only 25-40 % of the total water-soluble organic compounds were in the particle phase throughout the day.…”