[1] East Asia, including China, is the largest source of anthropogenic black carbon (BC). In estimating the BC emissions from this region, it is advantageous to use BC mass concentrations measured at remote locations on the ocean appropriately distant from the large sources because of spatially uniform distributions through mixing during transport. We made continuous measurements of the BC mass concentration with an accuracy of about 10% at Cape Hedo on Okinawa Island, Japan, in the East China Sea, from

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Abstract. In situ measurements of the mass concentration of black carbon (BC) and mixing ratios of carbon monoxide (CO) and carbon dioxide (CO 2 ) were made at Guangzhou, an urban measurement site in the Pearl River Delta (PRD), China, in July 2006. The average ± standard deviation (SD) concentrations of BC, CO, and CO 2 were 4.7±2.3 µgC m −3 , 798±459 ppbv, and 400±13 ppmv, respectively. The trends of these species were mainly controlled by synoptic-scale changes in meteorology during the campaign. Based on back trajectories, data are analyzed separately for two different air mass types representing northerly and southerly flows. The northerly air masses, which constituted ∼25% of the campaign, originated mostly in the PRD and hence represent observations on regional scales. On the other hand, during southerly flow (∼75%), the measurements were influenced by dilution due to cleaner marine air. The diurnal patterns of BC, CO, and CO 2 exhibited peak concentrations during the morning and evening hours coinciding with rush-hour traffic. The ratios of OC/BC were lower during the morning hour peaks in the concentrations of primary pollutants due to their fresh emissions mainly from vehicular traffic in Guangzhou. The diurnal variations of BC observed in southerly airCorrespondence to: Y. Kondo (y.kondo@atmos.rcast.u-tokyo.ac.jp) masses tended to follow the traffic patterns of heavy-duty vehicles (HDV) in Guangzhou, while the roles of other sources need to be investigated. The slopes of BC/ CO, BC/ CO 2 , and CO/ CO 2 observed during northerly flows were 0.0045 µgC m −3 /ppbv, 0.13 µgC m −3 /ppmv, and 49.4 ppbv/ppmv, respectively, agreeing reasonably with their respective emission ratios derived from regional emission inventories.

[1] Continuous in situ measurements of the mass concentration of black carbon (BC) aerosols and mixing ratio of carbon monoxide (CO) were made at Cape Hedo on Okinawa Island, Japan, a remote site located in the East China Sea, from March 2008 to May 2009. For the first time, we show temporal variations of BC and CO at Hedo in Asian outflows throughout the year. Annual average concentrations of BC and CO were 0.29 mg m −3 and 150 ppbv, respectively. The origins of the observed air masses were determined by using 5-day back trajectories, suggesting that about 51% of the air masses arriving at Hedo were from the Chinese region during spring and winter, while about 78% of air masses were of maritime origin during summer. Because of the more frequent transport of Chinese air to Hedo in spring and winter, the average and background concentrations of BC and CO in these seasons were higher by about a factor of 2 than those in summer and fall. Air masses from north China made the largest contributions to elevating the BC levels at Hedo because of the high BC emission rate and frequency of transport. The observed DBC/DCO ratio systematically decreased with the decrease in model-calculated transport efficiency (TE BC cal ). On the basis of this result, we derive region-specific DBC/DCO ratios by selecting data with TE BC cal > 80%. The annually averaged DBC/DCO ratios for air originated from north and south China were 7.0 ± 3.3 and 7.5 ± 4.6 ng m −3 ppbv −1 , respectively, about half the annual BC/CO emission ratio derived from the emission inventory of Zhang et al. (2009). We evaluate the CO emission inventory of Zhang et al. (2009) for China by comparing observed (ground-based and aircraft) and model-calculated CO values. The comparison indicates that the CO emissions from China were underestimated by about a factor of 2.

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