Abstract
Abstract. Secondary organic aerosol (SOA) formation from a cyclohexene ∕ NOx system with various SO2 concentrations under UV light was investigated to study the effects of cyclic alkenes on the atmospheric environment in polluted urban areas. A clear decrease at first and then an increase in the SOA yield was found with increasing SO2 concentrations. The lowest SOA yield was obtained when the initial SO2 concentration was in the range of 30–40 ppb, while higher SOA yield compared to that without SO2 could not be obtained until the initial SO2 concentration was higher than 85 ppb. The decreasing SOA yield might be due to the fact that the promoting effect of acid-catalysed reactions on SOA formation was less important than the inhibiting effect of decreasing OH concentration at low initial SO2 concentrations, caused by the competition reactions of OH with SO2 and cyclohexene. The competitive reaction was an important factor for SOA yield and it should not be neglected in photooxidation reactions. The composition of organic compounds in SOA was measured using several complementary techniques including Fourier transform infrared (FTIR) spectroscopy, ion chromatography (IC), and Exactive Plus Orbitrap mass spectrometer equipped with electrospray interface (ESI). We present new evidence that organosulfates were produced from the photooxidation of cyclohexene in the presence of SO2.
Highlights
Alkenes are widely emitted from biogenic and anthropogenic sources (Kesselmeier et al, 2002; Chin and Batterman, 2012), and their gas-phase oxidation reactions with OH, NO3, or O3 are among the most important processes in the atmosphere (Atkinson, 1997; Stewart et al, 2013; Paulson et al, 1999)
The reactor was surrounded by 12 black light lamps (GE F40BLB) with emission bands centred at 365 nm, which were used to simulate the spectrum of the UV band in solar irradiation
In the remainder of this paper, in order to better elaborate the effect of SO2 on the formation of particles, the particle number concentration refers to the particle number concentrations at the maximum secondary organic aerosol (SOA) yield
Summary
Alkenes are widely emitted from biogenic and anthropogenic sources (Kesselmeier et al, 2002; Chin and Batterman, 2012), and their gas-phase oxidation reactions with OH, NO3, or O3 are among the most important processes in the atmosphere (Atkinson, 1997; Stewart et al, 2013; Paulson et al, 1999). Reactions of ozone with alkenes are an important source of free radicals in the lower atmosphere and highly influence the oxidative capacity of the atmosphere (Paulson and Orlando, 1996). Some products of these reactions have sufficiently low vapour pressure, allowing them to condense with other gaseous species, and contribute to the secondary organic aerosol (SOA) mass (Sarwar and Corsi, 2007; Sakamoto et al, 2013; Nah et al, 2016; Kroll and Seinfeld, 2008; Hallquist et al, 2009). Cyclohexene has been extensively studied as a monoterpene surrogate for inferring oxidation mecha-
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