Study of Secondary Organic Aerosol Formation from Chlorine Radical-Initiated Oxidation of Volatile Organic Compounds in a Polluted Atmosphere Using a 3D Chemical Transport Model

Abstract

The impact of chlorine (Cl) chemistry on the formation of secondary organic aerosol (SOA) during a severe wintertime air pollution episode is investigated in this study. The Community Multiscale Air Quality (CMAQ) model v5.0.1 with a modified SAPRC-11 gas-phase mechanism and heterogeneous reactions for reactive chlorine species is updated to include the formation of chlorine radical (Cl•)-initiated SOA (Cl-SOA) from aromatic compounds, terpenes, and isoprene. Reported SOA yield data on Cl-SOA formation from environmental chamber studies are used to derive the mass yield and volatility data for the two-product equilibrium-partitioning model. The heterogeneous reaction of particulate chloride (pCl–) leads to a significant increase in the Cl• and hydroxyl radical (OH) concentrations throughout the domain. Monthly Cl-SOA concentrations range from 0.7 to 3.0 μg m–3, with increasing anthropogenic Cl emissions leading to higher Cl-SOA concentrations. Indirectly, this also leads to an increase of monthly SOA by up to 2.5–3.0 g μm–3 from the traditional OH oxidation pathways as well as the surface uptake of glyoxal and methylglyoxal. Increased OH concentrations, however, do not always lead to higher overall SOA concentrations in the entire domain. High OH reduces the lifetime of glyoxal/methylglyoxal (GLY/MGLY), making them less available to form SOA. In the Sichuan Basin (SCB) and part of Southwest China where high O3 concentrations meet high pCl emissions, a higher Cl•/OH ratio leads to net O3 loss from the Cl• + O3 reaction, thus reducing SOA formation from the O3 oxidation of volatile organic compounds (VOCs). Also, the competition between Cl• and OH for VOCs could lead to lower overall SOA because the molar yields of the semivolatile products in Cl-VOC reactions are lower than their OH + VOC reaction counterparts. When Cl• concentrations are further increased with higher emissions of Cl, precursor gases can be depleted and become the limiting factor in SOA formation. This study reveals the direct and indirect impacts of chlorine chemistry on SOA in polluted winter conditions, which are greatly affected by the Cl emissions, the ambient O3 level, and the availability of SOA precursors.

Source Apportionment and Toxicity of PM in Urban, Sub-Urban, and Rural Air Quality Network Stations in Catalonia

“…Primary organic sources in urban areas are related to combustion, cooking, industrial activities, soil and road dust, among others, while biomass burning and soil dust particles are dominant in rural areas [7][8][9]. The presence of oxidants in the atmosphere such as O 3 , NOx, and hydroxyl radicals interacts with primary emitted organics in complex reactions to form oxygenated products, such as dicarboxylic acids [10][11][12]. The oxygenated organic fraction in atmospheric PM can range from 20 to 90%, evidencing the need of understanding the role of the processes involved in SOA formation [13].…”

Comment on acp-2021-850

“…The NMB in the Base case therefore has decreased to -36% -39%. The slight underestimates at the Dongying site in the Base case could be to some extent explained by the bias in GFED4, which underestimates emissions from agricultural fires due to their small size and short duration as suggested by the study ofZhang et al (2020). In spite of that, the model with the Base case well reproduces the overall distribution of the observed particulate chloride concentrations in China.…”

The impact of chlorine chemistry combined with heterogeneous N<sub>2</sub>O<sub>5</sub> reactions on air quality in China

“…The global tropospheric chlorine by default in the model is mainly from the mobilization of Clfrom SSA distributed over two size bins (fine and coarse modes) (Wang et al, 2019), which is computed online as the integrals of the size-dependent source function depending on wind speeds and sea surface temperatures (Jaeglé et al, 2011). During the simulation year of 2018, SSA contributes 6.5 × 10 4 Gg Cl -, most of which however are distributed over the ocean due to its relatively short lifetime (∼1.5 days) (Choi et al, 2020). The release of atomic Cl from organic chlorine (CH3Cl, CH2Cl2 and CHCl3) via the oxidation by OH and Cl is also included in the model by default.…”

“…Recently, nitryl chloride (ClNO2), formed through the heterogeneous reaction between dinitrogen pentoxide (N2O5) and chloride-containing aerosols, is found to be another important source of tropospheric Cl atoms in polluted regions (Liu et al, 2018;Haskins et al, 2019;Choi et al, 2020). The heterogeneous formation of ClNO2 and the consequent photolysis can be described by reactions R1 -R4 shown below (Finlayson-Pitts et al, 1989;Osthoff et al, 2008).…”