Publication Date:
2014-08-26
Description:
Mass concentrations of black carbon (BC) in air ( M BC ) and rainwater ( C BC ) in the East China Sea were measured at Hedo on Okinawa Island, Japan from April 2010 to March 2013. The monthly averaged M BC and C BC showed marked seasonal variations, being highest in spring (0.32 ± 0.13 µg m −3 and 92 ± 76 µg L −1 , respectively), and lowest in summer (0.06 ± 0.03 µg m −3 and 8.0 ± 4.1 µg L −1 , respectively). The high M BC and C BC in spring were associated with transport of air masses from the Asian continent by northwesterly winds. The BC wet deposition flux ( F BC ), estimated as the product of C BC and precipitation amount, also showed a distinct seasonal variation. The monthly average F BC during the four spring seasons (16.8 ± 6.7 mg m −2 month −1 ) was about three times higher than the annual average F BC (5.5 ± 9.9 mg m −2 month −1 ) owing to the high C BC and precipitation amount in spring. As a result, about 76% of the annual BC deposition occurred in spring on average. The F BC in spring is comparable to the average BC net flux in North China, indicating the importance of precipitation over the East China Sea as a sink of BC transported from North China. In summer, C BC values were correlated with M BC for rain events associated with local convective activity, as identified by the convective available potential energy. A one-dimensional thermodynamic model successfully explained the relation between C BC and M BC .
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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