Distribution of ozone and related compounds in the marine boundary layer of the Northern South China Sea in 2010

Abstract

To investigate the characteristics of air pollutants transported from the Asian continental regions to the marine boundary layer of the northern South China Sea (SCS), we recorded the continuous measurements of meteorology, sea surface radiative budget, and ozone (O3) and related compounds in the marine boundary layer near Taiwan during 2010 cruises. For the marine field campaign investigation, the contaminated O3 and related compounds (e.g., NO2, NO, CO, CH4, and NMHC) have been eliminated from research vessel's exhaust by using various meteorological factors. The mean values of O3 and its major precursors (NO2, NO, and CO) were 25 ± 9.9, 3.2 ± 1.8, 2.9 ± 1.7, and 204 ± 54 ppb, respectively. A high O3 mixing ratio is related to extreme shortwave radiation, high air temperature, less precipitation, and low wind speed and specific humidity. The results indicated a higher ΔO3/ΔCO ratio of 0.2 at sunset during the March 2010 cruise mainly due to a long-range transport of aged plumes (> 3 days) originating from the super-region of Asian continent and a lower ?O3/?CO ratio of 0.12 at midday, mostly associated with the proximity to local sources of fresh plumes (> 2 days) during April 2010 and July 2010 cruises. The O3 and related compounds mixing ratios over the ocean are affected by emission source, Asian monsoon, wind speed, gas deposition, gas solubility, the chemical enhancement factor, the frontal inversion and the boundary layer height. A clear bulge in the diurnal cycle was observed between early morning and late afternoon for NOx, CO, and O3. Moreover, 5-d backward trajectories and Southeast Asia surface wind fields suggested that the southward export of the air masses in spring originated from Mongolia and the East Asian continent.