Abstract
Secondary organic aerosols (SOA) play an important role in global climate change and air quality, and SOA tracers can directly characterize the source and reaction mechanism of SOA. However, it is not well known that whether the tracers can be oxidized or how the instability of the tracers in the atmosphere. In this paper, in-situ FTIR was used to analyze the chemical structure changes of erythritol, analogue of 2-methyl erythritol (AME) that is, a tracer of isoprene SOA, and 2, 3-dihydroxy-4-oxopentanoic acid (DHOPA), a tracer of toluene SOA, when exposed to high concentration of ozone for short periods. Under the condition of 20 ppm ozone exposure for 30 min, the change rate of absorption area of AME at 3,480 and 1700 cm−1 was −0.0134 and 0.00117 int.abs/s, respectively, and the change rate of the absorption area of DHOPA at 1,640 and 3340cm−1 was −0.00191 and 0.00218 int.abs/s, respectively. The pseudo-first-order reaction rate constant kapp were 1.89 × 10−8 and 2.12 × 10−7 s−1, and the uptake coefficients of ozone on the surface of AME and DHOPA were (1.3 ± 0.8) × 10−8 and (4.5 ± 2.7) × 10−8, respectively. These results showed the oxidation processes of AME and DHOPA were slow in the presence of high concentrations of ozone, which implied that AME and DHOPA could be considered to be stable in the atmospheric environment with ozone as the main oxidant.
Highlights
Organic tracers have been used widely for source apportionment of organic aerosols under the assumption that they are not reactive in the atmosphere (Katrib et al, 2005; Kleindienst et al, 2007; Ding et al, 2012; Lai et al, 2014)
All chemicals used for this study had purity levels greater than 99%. -analogue of 2-methyl erythritol (AME) was supplied by Aladdin, and dihydroxy-4-oxopentanoic acid (DHOPA) was supplied by TRC
The pseudo-firstorder reaction rate constant kapp were 1.89 × 10−8 s−1 and 2.12 × 10−7 s−1, and the uptake coefficients of ozone on the surface of AME and DHOPA were (1.3 ± 0.8) × 10−8 and (4.5 ± 2.7) × 10−8, respectively. This experiment is the first time to study the uptake coefficient of AME and DHOPA, so we find the data of ozone heterogeneous oxidation of some other organic substances for comparison
Summary
Organic tracers have been used widely for source apportionment of organic aerosols under the assumption that they are not reactive in the atmosphere (Katrib et al, 2005; Kleindienst et al, 2007; Ding et al, 2012; Lai et al, 2014). Weitkamp et al studied the ozone oxidation of primary organic tracers of cooking oil emission (oleic acid, palmitoleic acid, and cholesterol etc.) through a series of chamber experiments. The results showed that the rate constant of ozone heterogeneous oxidation of oleic acid was 1.5 × 10−11 cm molec−1 sec−1, which was ten times of cholesterol and four times of palmitoleic acid (Weitkamp et al, 2008b). Lambe et al studied the effective reaction rate of oxidation reaction of norhopane, an organic tracer of motor oil by hydroxyl radical, and the rate constant of norhopane was 8.4 × 10−12 cm molec−1 s−1 (Lambe et al, 2009). The study of Hennigan et al indicated that rate constant of levoglucosan was 1.1 × 10−11 cm molecule−1s−1 when biomass burning particles were exposed to 1 × 106 molecules cm−3 of OH (Hennigan et al, 2010)
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