Open AccessMethyl chloride and other chlorocarbons in polluted air during INDOEX
Author(s) -
Scheeren H. A.,
Lelieveld J.,
de Gouw J. A.,
van der Veen C.,
Fischer H.
Publication year - 2002
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001jd001121
Subject(s) - environmental chemistry , chlorine , biomass burning , biofuel , biomass (ecology) , environmental science , dichloromethane , air mass (solar energy) , carbon monoxide , chloride , chemistry , aerosol , ecology , catalysis , organic chemistry , biology , physics , boundary layer , solvent , thermodynamics
Methyl chloride (CH 3 Cl) is the most abundant, natural, chlorine‐containing gas in the atmosphere, with oceans and biomass burning as major identified sources. Estimates of global emissions suffer from large uncertainties, mostly for the tropics, partly due to a lack of measurements. We present analyses of whole‐air canister samples for selected nonmethane hydrocarbons and chlorocarbons. The samples were collected from an aircraft during the Indian Ocean Experiment (INDOEX) campaign over the northern Indian Ocean in February and March 1999. The CH 3 Cl results are correlated to selected nonmethane hydrocarbons and in situ measurements of carbon monoxide (CO) and acetonitrile (CH 3 CN). We relate high mixing ratios of ∼750 pmol mol −1 of CH 3 Cl to biomass burning, as observed in polluted air masses from India and Southeast Asia. We infer a relatively high enhancement ratio relative to CO, ΔCH 3 Cl/ΔCO ≈1.74 ± 0.21 × 10 −3 mol mol −1 . The CH 3 Cl levels relate to the extensive biofuel use in India and Southeast Asia, notably the burning of agricultural waste and dung with a comparatively high chlorine content. It appears that CH 3 Cl emissions from biofuel consumption in India and Southeast Asia have been underestimated in the past. Furthermore, we observed enhanced dichloromethane (CH 2 Cl 2 ) and trichloromethane (CHCl 3 ) levels, correlating with high CO, acetylene (C 2 H 2 ) and CH 3 Cl, indicating that biomass burning is a small but significant source of these species.