The Variability of Relationship between Black Carbon and Carbon Monoxide over the Eastern Coast of China: BC Aging during Transport

East Asia is a densely populated region with a myriad of primary emissions of pollutants such as black carbon (BC) and carbon monoxide (CO). To characterize primary emissions over the eastern coast of China, a cascade of field campaign was conducted in 2011, including the measurement of ship cruise, island, and coastal receptor sites. The relationship between BC and CO is presented here for the first ship cruise (C1), the second ship cruise (C2), an island site (Changdao Island, CD), and a coastal site (Wenling, WL). The average BC mass concentrations are 2.43, 2.73, 1.09, 0.94, and 0.77 µg·m−3 for CD, WL, C1-YS (Yellow Sea), C1-ES (East China Sea), and C2-ES, respectively. For those locations, the average CO mixing ratios are 0.55, 0.48, 0.31, 0.36, and 0.27 ppm. The high loadings of both BC and CO imply the severe anthropogenic pollution over the eastern coast of China. Additionally, the linear correlation between BC and CO is regressed for each location. The slopes, i.e. ∆BC/∆CO ratios derived from their relationships are correlated well with the ratios of diesel consumption to gasoline consumption in each province/city, which reveals the vehicular emission as the common source for BC and CO and the distinct fuel structures between North and South China. The ∆BC/∆CO ratios at coastal sites (Changdao Island and Wenling) are much higher than those over Yellow Sea and East China Sea, and the correlation coefficients also show a decreasing trend from the coast to the sea. Therefore, the ∆BC/∆CO ratio and correlation coefficient are possible indicators for the aging and removal of BC.