Emissions of nonmethane volatile organic compounds from open crop residue burning in the Yangtze River Delta region, China
- 著者
- Kudo S., Tanimoto H., Inomata S., Saito S., Pan X. L., Kanaya Y., Taketani F., Wang Z., Chen H., Dong H., Zhang M., Yamaji K.
- 雑誌名
- J. Geophys. Res. Atmos., 119, 7684-7698
- DOI
- 10.1002/2013JD021044
- 概要
-
Open crop residue burning is one of the major sources of air pollutants including the precursors of photooxidants like ozone and secondary organic aerosol. We made measurements of trace gases including nonmethane volatile organic compounds (NMVOCs) in a rural area in central East China in June 2010. During the campaign, we identified six biomass burning events in total through the simultaneous enhancement of carbon monoxide and acetonitrile. Four cases represented fresh plumes (<2 h after emission), and two cases represented aged plumes (>3 h after emission), as determined by photochemical age. While we were not able to quantify formic acid, we identified an enhancement of major oxygenated volatile organic compounds (OVOCs) as well as low molecular alkanes and alkenes, and aromatic hydrocarbons in these plumes. The observed normalized excess mixing ratios (NEMRs) of OVOCs and alkenes showed dependence on air mass age, even in fresh smoke plumes, supporting the view that these species are rapidly produced and destructed, respectively, during plume evolution. Based on the NEMR data in the fresh plumes, we calculated the emission factors (EFs) of individual NMVOC. The comparison to previous reports suggests that the EFs of formaldehyde and acetic acid have been overestimated, while those of alkenes have been underestimated. Finally, we suggest that open burning of wheat residue in China releases about 0.34 Tg NMVOCs annually. If we applied the same EFs to all crops, the annual NMVOC emissions would be 2.33 Tg. The EFs of speciated NMVOCs can be used to improve the existing inventories.
2010年春季に中国江蘇省如東において大気汚染物質の集中観測を行ったところ、冬小麦収穫後のバイオマス燃焼の影響が見られた。そこで、排出インベントリに不確実性が非常に大きい非メタン揮発性有機化合物（NMVOCs）について、排出係数（EF）を導出し、排出量を見積もった。一酸化炭素とアセトニトリルが同時に増加する現象がバイオマス燃焼に特有であることを利用して、野焼きの発生源の実態を反映していると考えられる空気塊の特定を行った。そのデータをもとに、NMVOCsのEFを種類別に算出したところ、エチレン・プロピレン・アセトアルデヒド・ホルムアルデヒド・メタノールは、1g/kgを超える大きなEFを持つことが分かった。中国における小麦の野焼きによるNMVOCs排出量は0.34Tgとなり、全穀物に同じEFを仮定した場合は2.33Tg（人間活動による排出の5–10%程度）にもなった。このEFは既存のインベントリの改良に資すると考えられる。