Secondary aerosol formation and oxidation capacity in photooxidation in the presence of Al2O3 seed particles and SO2

Abstract

To investigate the sensitivity of secondary aerosol formation and oxidation capacity to NO x in homogeneous and heterogeneous reactions, a series of irradiated toluene/NO x /air and -pinene/NO x /air experiments were conducted in smog chambers in the absence or presence of Al 2 O 3 seed particles. Various concentrations of NO x and volatile organic compounds (VOCs) were designed to simulate secondary aerosol formation under different scenarios for NO x . Under "VOC-limited" conditions, the increasing NO x concentration suppressed secondary aerosol formation, while the increasing toluene concentration not only contributed to the increase in secondary aerosol formation, but also led to the elevated oxidation degree for the organic aerosol. Sulfate formation was suppressed with the increasing NO x due to a decreased oxidation capacity of the photooxidation system. Secondary organic aerosol (SOA) formation also decreased with the presence of high concentration of NO x , because organo-peroxy radicals (RO 2 ) react with NO x instead of with peroxy radicals (RO 2 or HO 2 ), resulting in the formation of volatile organic products. The increasing concentration of NO x enhanced the formation of sulfate, nitrate and SOA under "NO x -limited" conditions, in which the heterogeneous reactions played an important role. In the presence of Al 2 O 3 seed particles, a synergetic promoting effect of mineral dust and NO x on secondary aerosol formation in heterogeneous reactions was observed in the photooxidation. This synergetic effect strengthened the positive relationship between NO x and secondary aerosol formation under "NO x -limited" conditions but weakened or even overturned the negative relationship between NO x and secondary aerosol formation under "VOC-limited" conditions. Sensitivity of secondary aerosol formation to NO x seemed different in homogeneous and heterogeneous reactions, and should be both taken into account in the sensitivity study. The sensitivity of secondary aerosol formation to NO x was further investigated under "winter-like" and NH 3 -rich conditions. No obvious difference for the sensitivity of secondary aerosol formation except nitrate to NO x was observed. secondary aerosol, oxidation capacity, synergetic promoting effect, Al 2 O 3 seed particles, sensitivity

Effects of SO<sub>2</sub> on optical properties of secondary organic aerosol generated from photooxidation of toluene under different relative humidity conditions

“…At the end of the experiments, the S tot of particles were approximately 2.9 × 10 9 , 4.3 × 10 9 , 3.8 × 10 9 and 6.9 × 10 9 nm 2 cm −3 under the D, DS, W and WS conditions, respectively. The addition of SO 2 caused an enhancement of the total surface concentrations of the particles, probably because of the formation of new particles and/or acidiccatalyzed reactions, as implied in previous studies (Chu et al, 2016;Deng et al, 2017;Hallquist et al, 2009). Moreover, the S tot under wet conditions was higher than that under dry conditions as well, probably due to aqueous reactions of water soluble products, as indicated previously (Jia and Xu, 2018;Kamens et al, 2011;Hinks et al, 2018).…”

“…These products are mainly alcohols and esters with smaller molecular weight and RI(n) values of which are lower than 1.4. The reason for this is most likely that the addition of SO 2 caused large amounts of new particle formation and high particle number concentrations in the system (Chu et al, 2015(Chu et al, , 2016Deng et al, 2017;Liu et al, 2019), which could provide a larger mass concentration and adsorb highly volatile small molecules into the particle phase (K. . These small molecule products usually possess high volatility and a low oxidation state, which would also reduce the oxidation state of aerosols generated by toluene.…”

Inhibition Effect of Negative Air Ions on Adsorption between Volatile Organic Compounds and Environmental Particulate Matter

“…Volatile organic compounds (VOCs) as toxic environmental pollutants have been drawing more and more attention due to many diseases being attributed to air pollution. − As one of the most important components of ambient air, particulate matter (PM) is a key indicator of air pollution, and it is not a single contaminant but a mixture containing NO x , toxic organics, and some heavy metals. − Many studies have proved the increased risk of health problems associated with the long-term inhalation of PM, such as the increased hospitalization and mortality caused by acute respiratory problems and the increased incidence and severity of lung cancer. − The toxicity of PM depends on its composition and the size distribution: the smaller the size of PM, the more dangerous it is to one’s health because it can penetrate the respiratory tract and reach the alveoli.…”

Atmospheric Processes of Aromatic Hydrocarbons in the Presence of Mineral Dust Particles in an Urban Environment

“…Most studies have focused on the heterogeneous uptake of inorganic trace gases on dust particles, − and few studies have attempted to investigate the uptake of VOCs on mineral dust particles. − Some VOCs can undergo photooxidation in the atmosphere and produce semi-VOCs (SVOCs). SVOCs play an important role in secondary organic aerosol (SOA) formation, which is a major contributor to the organic carbon budget on a global scale − and in the urban atmosphere .…”