Re-examination of C1-C5alkyl nitrates in Hong Kong using an observation-based model

X. P. Lyu, Z. H. Ling, Hai Guo, S. M. Saunders, S. H.M. Lam, N. Wang, Y. Wang, M. Liu, Tao Wang

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Abstract

The photochemical formation of alkyl nitrates (RONO2) and their impact on ozone (O3) formation were investigated using a Photochemical Box Model incorporating the Master Chemical Mechanism (PBM-MCM). The model was constrained with field measurement data collected on selected O3episode days at Tai O, a rural-coastal site in southwestern Hong Kong, from August 2001-December 2002. The in-situ observations showed that the sum of C1-C5RONO2varied from 30.7 ± 14.8 pptv in spring to 120.7 ± 10.4 pptv in autumn, of which 2-butyl nitrate dominated with the highest average concentration of 30.8 ± 2.6 pptv. Model simulations indicated that the pathway of CH3O reacting with NO2, proposed in our previous study, made minor contributions (11.3 ± 0.7%) to methyl nitrate formation. Indeed, 51.8 ± 3.1% and 36.5 ± 6.3% of the methyl nitrate was attributed to the reaction of CH3O2+NO and to oceanic emissions/biomass burning, respectively. For the C2-C5alkyl nitrates, the contribution of photochemical formation increased with increasing carbon number, ranging from 64.4 ± 4.0% for ethyl nitrate (EtONO2) to 72.6 ± 4.2% for 2-pentyl nitrate (2-PenONO2), while the contribution of oceanic emissions/biomass burning decreased from 35.1 ± 6.5% for EtONO2to 26.8 ± 6.8% for 2-PenONO2. Model simulations of photochemical O3levels influenced by RONO2chemistry showed that the formation of methyl-, ethyl-, i-propyl-, n-propyl-, 2-butyl-, 2-pentyl-, and 3-pentyl-nitrates led to O3reduction of 0.05 ± 0.03, 0.05 ± 0.03, 0.06 ± 0.02, 0.02 ± 0.02, 0.18 ± 0.04, 0.09 ± 0.02 and 0.06 ± 0.02 ppbv, respectively, with an average reduction rate of 11.0 ± 3.2 ppbv O3per 1 ppbv RONO2formation. The C1-C5RONO2constituted 18.6 ± 1.9% of the entire RONO2, and had a nitrogen reserve of 4.1 ± 0.2%, implying their potential influence on O3production in downwind areas.
Original languageEnglish
Pages (from-to)28-37
Number of pages10
JournalAtmospheric Environment
Volume120
DOIs
Publication statusPublished - 1 Nov 2015

Keywords

  • Alkyl nitrate
  • Field observation
  • O production 3
  • PBM-MCM model
  • Photochemical formation

ASJC Scopus subject areas

  • Environmental Science(all)
  • Atmospheric Science

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