Abstract
Abstract. Rate coefficients for the reaction of NO3 radicals with a series of aromatic aldehydes were measured in a 7300 L simulation chamber at ambient temperature and pressure by relative and absolute methods. The rate coefficients for benzaldehyde (BA), ortho-tolualdehyde (O-TA), meta-tolualdehyde (M-TA), para-tolualdehyde (P-TA), 2,4-dimethyl benzaldehyde (2,4-DMBA), 2,5-dimethyl benzaldehyde (2,5-DMBA) and 3,5-dimethyl benzaldehyde (3,5-DMBA) were k1= 2.6 ± 0.3, k2= 8.7 ± 0.8, k3= 4.9 ± 0.5, k4= 4.9 ± 0.4, k5= 15.1 ± 1.3, k6= 12.8 ± 1.2 and k7= 6.2 ± 0.6, respectively, in the units of 10−15 cm3 molec.−1 s−1 at 298 ± 2 K. The rate coefficient k13 for the reaction of the NO3 radical with deuterated benzaldehyde (benzaldehyde-d1) was found to be half that of k1. The end product of the reaction in an excess of NO2 was measured to be C6H5C(O)O2NO2. Theoretical calculations of aldehydic bond energies and reaction pathways indicate that the NO3 radical reacts primarily with aromatic aldehydes through the abstraction of an aldehydic hydrogen atom. The atmospheric implications of the measured rate coefficients are briefly discussed.
Highlights
Aromatic aldehydes are a family of organic compounds emitted into the atmosphere from anthropogenic and pyrogenic sources
Benzaldehyde and ortho, meta- and para-tolualdehyde could be formed from the atmospheric degradation of aromatic hydrocarbons, their yields in the atmosphere are expected to be small (Calvert et al, 2002; Obermeyer et al, 2009)
MMA, was used as the reference compound in this work because the rate coefficient at 298 K for its reaction with the NO3 radical has been measured in the same chamber using the same method as used here (Zhou et al, 2017) to be kMMA = (2.98±0.35)×10−15 cm3 molec.−1 s−1
Summary
Aromatic aldehydes are a family of organic compounds emitted into the atmosphere from anthropogenic and pyrogenic sources. Oxidation of aromatic aldehydes via their reaction with the nitrate radical, NO3, may be important in NOx-rich locations at night since both the aromatic aldehydes and the nitrate radical can arise from anthropogenic emissions and pyrogenic sources. To the best of our knowledge, there are no studies that have measured the formation of secondary organic aerosol (SOA) from the title reaction in either a chamber or in the atmosphere. One could suspect that aromatic aldehydes may be degraded at night with consequences for ozone and SOA formation. The rate coefficients k1–k7 at 298 K for the reactions of the NO3 radical with the following seven aromatic aldehydes were measured. We report the rate coefficients at 298 K for the above reactions, and we have determined the stable products formed in Reaction (R1). Ren et al.: Reactions of NO3 with aromatic aldehydes tution, quantum chemistry calculations and an examination of the linear free-energy relationship
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