Analysis of CCN activity of Arctic aerosol and Canadian biomass burning during summer 2008

Abstract

The NASA DC-8 aircraft characterized the aerosol properties, chemical composition, and cloud condensation nuclei (CCN) concentrations of the summertime Arctic during the 2008 NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) campaign. Air masses characteristic of fresh and aged biomass burning, boreal forest, Arctic background, and anthropogenic industrial pollution were sampled. Observations were spatially extensive (50–85° N and 40–130° W) and exhibit significant variability in aerosol and CCN concentrations. The chemical composition was dominated by highly oxidized organics (66–94% by volume), with a water-soluble mass fraction of more than 50%. The aerosol hygroscopicity parameter, κ, ranged between κ = 0.08–0.32 for all air mass types. Industrial pollution had the lowest κ of 0.08 ± 0.01, while the Arctic background had the highest and most variable κ of 0.32 ± 0.21, resulting from a lower and more variable organic fraction. Both fresh and aged (long-range transported) biomass burning air masses exhibited remarkably similar κ (0.18 ± 0.13), consistent with observed rapid chemical and physical aging of smoke emissions in the atmosphere, even in the vicinity of fresh fires. The organic hygroscopicity (κ_org) was parameterized by the volume fraction of water-soluble organic matter (ε_WSOM), with a κ = 0.12, such that κ_org = 0.12ε_WSOM. Assuming bulk (size-independent) composition and including the κ_org parameterization enabled CCN predictions to within 30% accuracy for nearly all environments sampled. The only exception was for industrial pollution from Canadian oil sands exploration, where an external mixture and size-dependent composition was required. Aerosol mixing state assumptions (internal vs. external) in all other environments did not significantly affect CCN predictions; however, the external mixing assumption provided the best results, even though the available observations could not determine the true degree of external mixing and therefore may not always be representative of the environments sampled. No correlation was observed between κ_org and O : C. A novel correction of the CCN instrument supersaturation for water vapor depletion, resulting from high concentrations of CCN, was also employed. This correction was especially important for fresh biomass burning plumes where concentrations exceeded 1.5×10⁴ cm^−3 and introduced supersaturation depletions of ≥25%. Not accounting for supersaturation depletion in these high concentration environments would therefore bias CCN closure up to 25% and inferred κ by up to 50%

Cloud condensation nucleus activity comparison of dry- and wet-generated mineral dust aerosol: the significance of soluble material

“…Observational studies have shown that typical atmospheric aerosols have κ between 0.1 and 0.4 (Andreae and Rosenfeld, 2008;Juranyi et al, 2010;Friedman et al, 2013;Lathem et al, 2013). For the materials considered in this study, hygroscopicity tandem differential mobility analyzer (HTDMA) measurements suggest that κ = 0.003 for both dry-and wet-generated ATD, illite, and NaMon (Herich et al, 2009).…”

Understanding the contributions of aerosol properties and parameterization discrepancies to droplet number variability in a global climate model

“…The assumed hygroscopicity of SOA and POM of κ soa = 0.14 and κ pom = 0.1 respectively (Table 1); however, there is a wide range of values reported for these parameters in the literature (e.g., Lathem et al, 2013). For application of Eq.…”

CCN activity and organic hygroscopicity of aerosols downwind of an urban region in central Amazonia: seasonal and diel variations and impact of anthropogenic emissions

“…During non-IOP periods, only the total nitrate mass concentration is available, all nitrate was assumed to be an organonitrate (Cerully et al, 2015;Lathem et al, 2013;Nenes et al, 1998;Zhang et al, 2005), and sulfate was fully neutralized by ammonium (see Sect. S4.2 in the Supplement for a sensitivity study of these assumptions for non-IOP periods).…”

“…However, atmospheric aerosols consist of a large number of organic compounds, which often dominate the total fine aerosol mass, especially in forested areas (e.g., de Sá et al, 2017a;Zhang et al, 2007). The hygroscopicity of aerosol organics (κ org ) have been examined in both laboratory (e.g., Asa-Awuku et al, 2009;Duplissy et al, 2011;King et al, 2009;Lambe et al, 2011;Massoli et al, 2010;Raymond and Pandis, 2003) and field studies (e.g., Cerully et al, 2015;Chang et al, 2010;Dusek et al, 2010;Gunthe et al, 2009;Lathem et al, 2013;Mei et al, 2013a, b;Moore et al, 2011Moore et al, , 2012Pöhlker et al, 2016;Rose et al, 2010;Shantz et al, 2008;Wang et al, 2008). Overall, these studies show that aerosol organics exhibit a wide range of κ values from 0 to ∼ 0.3, and κ org often increases substantially during aerosol aging in the atmosphere (e.g., Duplissy et al, 2011;Lambe et al, 2011;Massoli et al, 2010;Mei et al, 2013a, b).…”