During the ACE-Asia intensive field campaign (March 14-April 20,2001), PM1.0 organic (OC) and elemental carbon (EC) concentrations were measured onboard the NOAA RIV Ronald H. Brown over the Northwest Pacific Ocean using a semi-continuous automated carbon analyzer downstream of a carbon-impregnated filter denuder. This OC and EC measurement achieved a mean time resolution of about 200 min over the Pacific Ocean, substantially lower than that achieved previously (24 h). The semi-continuous measurements, in which the adsorption artifact was substantially reduced using the denuder, showed good agreement with integrated artifact-corrected measurements made without a denuder. Mean particulate OC and EC concentrations were 0.21 and 0.09, 0.70 and 0.29, 1.00 and 0.27, and 2.43 and 0.66μg of C m{sup}(-3) over the background Pacific Ocean, Asian-influenced Pacific Ocean, offshore of Japan, and Sea of Japan, respectively. On April 11, 90-min average OC and EC concentrations peaked at 4.0 and 1.3μg of C m{sup}(-3), respectively, offshore of Korea over the Sea of Japan. The OC/EC ratio of 3.7 over the Sea of Japan and offshore of Japan was substantially higher than that of 2.5 over the Asian-influenced Pacific Ocean, even though backward air mass trajectories put the "Asian-influenced Pacific Ocean" sample downwind. The OC/EC ratio decreased with increasing time since the air mass encountered the source regions of China, Japan, and Korea. This suggests a longer atmospheric residence time for EC than for OC.
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