Smog chamber study of the effects of NOx and NH3 on the formation of secondary organic aerosols and optical properties from photo-oxidation of toluene

Reviewer comment on acp-2021-560

“…There was a noticeable increase in the SOA mass concentration in the presence of NH3. The mass concentration of SOA increased from 637 ± 14.6 μg m -3 without NH3 to a maximum of 867 ± 12.7 μg m -3 with 200 ppb NH3, consistent with previous studies (Na et al, 2007;Qi et al, 2020 (Zhao et al, 2018;Liu et al, 2019a;Xu et al, 2020). Highly volatile compounds cannot readily participate into the particle-phase, so this substantially suppresses the formation of SOA.…”

“…increased aerosol size growth potentials (by 7%-108%), and resulted in enhanced SOA formation. Qi et al (2020) found that the concentration and average diameter of SOA showed an immediate and rapid increase after adding NH3. Furthermore, the acid-base reactions between NH3/NH4 + and the carboxyl groups in SOA molecules might enhance SOA formation (Qi et al, 2020;Liu et al, 2015).…”

“…Qi et al (2020) found that the concentration and average diameter of SOA showed an immediate and rapid increase after adding NH3. Furthermore, the acid-base reactions between NH3/NH4 + and the carboxyl groups in SOA molecules might enhance SOA formation (Qi et al, 2020;Liu et al, 2015). The condensable ammonium salts formed from the reaction between NH3 and organic acids reduce the volatility of the organic acids by several orders of magnitude (Paciga et al, 2014), and act as particlephase organics that further promote SOA formation (Na et al, 2007;Huang et al, 2012;Chen et al, 2019;Qi et al, 2020).…”

“…Furthermore, the acid-base reactions between NH3/NH4 + and the carboxyl groups in SOA molecules might enhance SOA formation (Qi et al, 2020;Liu et al, 2015). The condensable ammonium salts formed from the reaction between NH3 and organic acids reduce the volatility of the organic acids by several orders of magnitude (Paciga et al, 2014), and act as particlephase organics that further promote SOA formation (Na et al, 2007;Huang et al, 2012;Chen et al, 2019;Qi et al, 2020). Along another pathway, glyoxal can undergo nucleophilic attack by NH3 through the Maillard reactions and form the corresponding iminium intermediates (Nozière et al, 2009;Laskin et al, 2015;Liu et al, 2015).…”

“…Both Nozière et al (2009) and Ortiz- Montalvo et al (2014) reported NH3 is an efficient catalyst for reactions with carbonyl compounds to form nitrogen-containing compounds (NOCs). The reaction between carbonyl and NH3 can significantly decrease the volatility of oxidation products, which further increases the yield of SOA (Lee et al, 2013;Zhang et al, 2015;Qi et al, 2020). Babar et al (2017) found that the substantial formation of secondary imines in the presence of NH3 was responsible for the higher α-pinene SOA yields.…”