Modeling reactive ammonia uptake by secondary organic aerosol in CMAQ: application to the continental US

Abstract

Ammonium salts such as ammonium nitrate and ammonium sulfate constitute an important fraction of the total fine particulate matter (PM 2.5 ) mass. While the conversion of inorganic gases into particulate-phase sulfate, nitrate, and ammonium is now well understood, there is considerable uncertainty over interactions between gas-phase ammonia and secondary organic aerosols (SOAs). Observations have confirmed that ammonia can react with carbonyl compounds in SOA, forming nitrogen-containing organic compounds (NOCs). This chemistry consumes gas-phase NH 3 and may therefore affect the amount of ammonium nitrate and ammonium sulfate in particulate matter (PM) as well as particle acidity. In order to investigate the importance of such reactions, a first-order loss rate for ammonia onto SOA was implemented into the Community Multiscale Air Quality (CMAQ) model based on the ammonia uptake coefficients reported in the literature. Simulations over the continental US were performed for the winter and summer of 2011 with a range of uptake coefficients (10 −3 -10 −5 ). Simulation results indicate that a significant reduction in gas-phase ammonia may be possible due to its uptake onto SOA; domainaveraged ammonia concentrations decrease by 31.3 % in the winter and 67.0 % in the summer with the highest uptake coefficient (10 −3 ). As a result, the concentration of particulate matter is also significantly affected, with a distinct spatial pattern over different seasons. PM concentrations decreased during the winter, largely due to the reduction in ammonium nitrate concentrations. On the other hand, PM concentrations increased during the summer due to increased biogenic SOA (BIOSOA) production resulting from enhanced acid-catalyzed uptake of isoprene-derived epoxides. Since ammonia emissions are expected to increase in the future, it is important to include NH 3 + SOA chemistry in air quality models.

High secondary formation of nitrogen-containing organics (NOCs) and its possible link to oxidized organics and ammonium

“…However, the relatively weak correlation (R 2 = 0.27, p < 0.01) between the peak ratios and the RH reflects the complex influence of the RH on the formation of NOCs (Xu et al, 2017;Woo et al, 2013). One may expect that NOCs are formed through the interactions between NO x and oxidized organics in the gas phase, followed by condensation (Fry et al, 2014;Ziemann and Atkinson, 2012;Seinfeld and Pandis, 2006). Similar to the behavior observed for RH, NOCs do not show a clear dependence on NO x (Fig.…”

“…Emissions of primary NOCs have been attributed to biomass burning, coal combustion, vehicle emissions, biogenic production, and soil dust (Laskin et al, 2009;Desyaterik et al, 2013;Sun et al, 2017;Mace et al, 2003;Rastogi et al, 2011;Wang et al, 2017). Secondary NOCs, such as organic nitrates and nitroaromatic compounds, are believed to be mainly formed in the gas phase by interaction between volatile organic compounds (VOCs) and oxidants (e.g., NO x , • OH), followed by condensation to aerosols (Ziemann and Atkinson, 2012;Seinfeld and Pandis, 2006). Recently, another group of secondary NOCs, or heterocyclic NOCs, formed by reactions involving mixtures of atmospheric aldehydes (e.g., methylglyoxal/glyoxal) and ammonium (NH + 4 )/amines has been of particular interest (e.g., Hawkins et al, 2016;De Haan et al, 2011.…”

Direct contribution of ammonia to &lt;i&gt;α&lt;/i&gt;-pinene secondary organic aerosol formation

“…Our results may prompt us to reconsider the pathway of gas-phase organic acids involved in SOA formation in the atmosphere, whether they directly participate in partitioning between the gas and particle phases or they undergo secondary conversion via reaction with NH 3 before they condensate on the particle phase in the atmosphere. After SOAs are formed, the carbonyl group of chemical compounds in SOA particles can also uptake NH 3 heterogeneously to form nitrogencontaining compounds (Zhu et al, 2018;Updyke et al, 2012;Dinar et al, 2008) and organic ammonium salts (Schlag et al, 2017). In this study the N : C ratios measured by AMS were nearly constant or slightly increasing in two sets of experiments ( Fig.…”

“…Besides, the addition of NH 3 could also promote the SOA formation from photooxidation of vehicle exhaust (Chen et al, 2019;, anthropogenic VOCs (Wang et al, 2018;Huang et al, 2018) and acrolein (Li et al, 2019). The promotion mechanism of NH 3 to SOA formation can be both through base-acid reaction (Schlag et al, 2017;Babar et al, 2017;Rubach et al, 2013;Mensah et al, 2012;Na et al, 2007) and by the NH 3 uptake to the carbonyl group (Zhu et al, 2018;. As a consequence, the changes in particle size and chemical composition could alter the CCN ability and hygroscopicity of SOA particles (Dinar et al, 2008).…”

Modeling the Sources and Transport Processes During Extreme Ammonia Episodes in the U.S. Corn Belt

“…These data were provided by the U.S. Environmental Protection Agency (EPA) air quality system (https://aqs.epa.gov/api). Such data have been widely used to evaluate atmospheric model performance (Hu et al, 2013;Yegorova et al, 2011;Zhu et al, 2018). Supporting meteorological data including wind direction (WD), wind speed (WS), 2-m air temperature (T 2 ), and relative humidity (RH) were measured at the US-Ro1 Ameriflux site, which is located within 5 km of the KCMP tall tower.…”