Nitrous acid (HONO) in a polluted subtropical atmosphere: Seasonal variability, direct vehicle emissions and heterogeneous production at ground surface

Zheng Xu, Tao Wang, Jueqi Wu, Likun Xue, James Chan, Qiaozhi Zha, Shengzhen Zhou, Peter K.K. Louie, Connie W.Y. Luk

Research output: Journal article publicationJournal articleAcademic researchpeer-review

68 Citations (Scopus)


Although nitrous acid (HONO) plays an important role in the chemistry of polluted atmospheres, its atmospheric abundances and sources are still not well understood. This paper reports ambient measurements of HONO taken over four select months in different seasons at a suburban site in Hong Kong. The data were analyzed to elucidate the seasonal characteristics, emission ratios and rates of heterogeneous production. The monthly averaged HONO concentrations ranged from 0.35±0.30ppbv in late spring (May) to 0.93±0.67ppbv in late autumn (November). The similar variation patterns of HONO, NOx,and traffic flow from midnight to rush hours suggest that the HONO concentration was strongly influenced by vehicle emissions. The emission ratios (HONO/NOx) were derived from an analysis of 21 fresh plumes (NO/NOx0.80), with the range of 0.5-1.6%. The large variability in the emission ratios is attributed to the reaction of NO2on black carbon (BC) emitted from vehicles, based on a strong correlation between the HONO/NOxand concurrently measured BC. The mean conversion rate of NO2to HONO on ground surface during nighttime estimated on nine select days was 0.52 × 10-2h-1, which is relatively low compared with other reported values. This paper highlights a large variability in vehicle emission ratios and heterogeneous conversions of NO2at ground surface. Photochemical models must consider this variability to better simulate the primary sources of HONO and subsequent photochemistry in the lower part of the troposphere.
Original languageEnglish
Pages (from-to)100-109
Number of pages10
JournalAtmospheric Environment
Publication statusPublished - 1 Apr 2015


  • Black carbon
  • Heterogeneous reaction
  • Nitrous acid
  • Seasonal variation
  • Vehicle emission

ASJC Scopus subject areas

  • Environmental Science(all)
  • Atmospheric Science

Cite this