Observations of high rates of NO2-HONO conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal
Artikel i vetenskaplig tidskrift, 2009

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 atmosphere 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 urban air in Kathmandu. Surprisingly high ratios of chemically formed secondary [HONO] to [NO2] (up to 30%) were found, which indicates unexpectedly efficient chemical conversion 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 particularly efficient conversion of NO2 to HONO.

simulated vertical profiles

absorption cross-sections

mass accommodation coefficients



mineral dust particles

heterogeneous no2



nitrous-acid hono

path field-measurements



Yu Yong

Chalmers, Institutionen för radio- och rymdvetenskap

Bo Galle

Chalmers, Institutionen för radio- och rymdvetenskap, Optisk fjärranalys

A. Panday

Massachusetts Institute of Technology (MIT)

Princeton University

E. Hodson

Eidgenossische Forschungsanstalt fur Wald, Schnee Und Landschaft Eth-Bereichs

Massachusetts Institute of Technology (MIT)

R. Prinn

Massachusetts Institute of Technology (MIT)

S. Wang

Jet Propulsion Laboratory, California Institute of Technology

Atmospheric Chemistry and Physics

1680-7316 (ISSN) 1680-7324 (eISSN)

Vol. 9 17 6401-6415


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