Atmospheric Organic Aerosol Production by Heterogeneous Acid‐Catalyzed Reactions

Abstract

Exploratory evidence from our laboratories shows that acidic surfaces on atmospheric aerosols lead to very real and potentially multifold increases in secondary organic aerosol (SOA) mass and build-up of stabilized nonvolatile organic matter as particles age. One possible explanation for these heterogeneous processes are the acid-catalyzed (e.g., H2SO4 and HNO3) reactions of atmospheric multifunctional organic species (e.g., multifunctional carbonyl compounds) that are accommodated onto the particle phase from the gas phase. Volatile organic hydrocarbons (VOCs) from biogenic sources (e.g., terpenoids) and anthropogenic sources (aromatics) are significant precursors for multifunctional organic species. The sulfur content of fossil fuels, which is released into the atmosphere as SO2, results in the formation of secondary inorganic acidic aerosols or indigenous acidic soot particles (e.g., diesel soot). The predominance of SOAs contributing to PM2.5 (particulate matter, that is, 2.5 microm or smaller than 2.5 microm), and the prevalence of sulfur in fossil fuels suggests that interactions between these sources could be considerable. This study outlines a systematic approach for exploring the fundamental chemistry of these particle-phase heterogeneous reactions. If acid-catalyzed heterogeneous reactions of SOA products are included in next-generation models, the predicted SOA formation will be much greater and have a much larger impact on climate-forcing effects than we now predict. The combined study of both organic and inorganic acids will also enable greater understanding of the adverse health effects in biological pulmonary organs exposed to particles.

Secondary Particulate Matter in the United States: Insights from the Particulate Matter Supersites Program and Related Studies

“…12 In addition to gas-phase reactions, particle phase heterogeneous reactions also can produce additional SOA material. This has been observed in laboratory studies of acid-catalyzed organic reactions that form SOA, [13][14][15][16][17][18] and isoprene oxidation to form SOA in clouds has been modeled successfully. 19 However, recent work in Pittsburgh observed little impact of acid-catalyzed organic reactions in ambient air.…”

“…However, recent evidence suggests that once the oxidation products condense into the particle phase, heterogeneous particle-phase reactions may occur leading to even lower volatility organics, and thus, increasing SOA levels in the atmosphere. 35 As mentioned in the introduction, one of the most interesting developments concerning heterogeneous SOA formation is the demonstration of acid-catalyzed organic reactions leading to increased SOA production in the laboratory, [13][14][15][16][17][18] although the influence of acid-catalyzed SOA formation was not observed in ambient air in Pittsburgh. 20 For a variety of organic precursors, including biogenics and aldehydes, the presence of an acidified seed aerosol led to multifold increases in SOA production compared with a nonacidic seed.…”

Hydrolysis of Organonitrate Functional Groups in Aerosol Particles

“…Figures 5b and 6 suggest that the greater loss rate of the nitrate mass fraction at RH > 20% resulted from true loss of nitrate rather than from a dilution effect due to continued production of non-nitrate OM. In contrast, the decrease of nitrate mass fraction over time at RH < 20% (Figure 6) could be explained by OM production (Figure 5b), which was likely the result of either multigenerational chemistry (Robinson et al 2007) or polymer formation, a reaction that is typically highly unfavorable when RH is high (Jang et al 2002(Jang et al , 2004. Although Kalberer et al (2004) proposed that polymer formation of 1,3,5-TMB oxidation products initiates with hydration of methylglyoxal, which requires water, polymer formation proceeds by condensation processes that generate water and are likely inhibited by aerosol water at high RH.…”

The formation, properties and impact of secondary organic aerosol: current and emerging issues

“…The first studies were based on indirect evidence, i.e., increased SOA mass concentration observed in the presence of acidic seed aerosol Jang et al, 2002Jang et al, , 2004Limbeck et al, 2003). Although it was proposed that polymerization reactions of volatile carbonyls may account for the observed SOA mass increase, there was no direct evidence to support this at the time.…”