Observations of high rates of NO 2 -HONO conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal

Nitrous acid (HONO) plays a significant role in the atmosphere, especially in the polluted troposphere. Its photolysis after sunrise is an important source of hydroxyl free radicals (OH). Measurements of nitrous acid and other pollutants were carried out in the Kathmandu urban atmo- sphere during January-February 2003, contributing to the sparse knowledge of nitrous acid in South Asia. The results showed average nocturnal levels of HONO (1.7±0.8 ppbv), NO2 (17.9±10.2 ppbv), and PM10(0.18±0.11 mg m 3 ) in ur- ban air in Kathmandu. Surprisingly high ratios of chemi- cally formed secondary (HONO) to (NO2) (up to 30%) were found, which indicates unexpectedly efficient chemical con- version of NO2 to HONO in Kathmandu. The ratios of (HONO)/(NO2) at night were found to be much higher than previously reported values from measurements in urban air in Europe, North America and Asia. The influences of aerosol surface, ground reactive surface, and relative humidity on NO2-HONO chemical conversion were discussed. The high humidity, strong and low inversion layer at night, and high aerosol pollution burden in Kathmandu may explain the par- ticularly efficient conversion of NO 2 to HONO.

• Publication year

  2009

• Venue

  Atmospheric Chemistry and Physics

• Publication date

  2009-09-07

• Fields of study

  Chemistry, Environmental Science

• Identifiers
  DOI 10.5194/ACP-9-6401-2009
• External record

  Open on Semantic Scholar

• Source metadata

  Semantic Scholar

• No claims are published for this paper.

• No concepts are published for this paper.

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