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 (O 3 ) and related compounds in the marine boundary layer near Taiwan during 2010 cruises. For the marine field campaign investigation, the contaminated O 3 and related compounds (e.g., NO 2 , NO, CO, CH 4 , and NMHC) have been eliminated from research vessel's exhaust by using various meteorological factors. The mean values of O 3 and its major precursors (NO 2 , NO, and CO) were 25 ± 9.9, 3.2 ± 1.8, 2.9 ± 1.7, and 204 ± 54 ppb, respectively. A high O 3 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 ∆O 3 /∆CO 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 ∆O 3 /∆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 O 3 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 NO x , CO, and O 3 . 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.

Chemical interactions between ship-originated air pollutants and ocean-emitted halogens

“…The discrepancy between model and measurements could be due to (1) different period between model and field campaigns; (2) different spatial dimensions and range (a single point in ground campaigns and a 3D line for flight campaigns compared to a 27 × 27 km 2 grid box in the model); (3) uncertainty in the emission inventory from shipping and the islands within the domain; and (4) missing sources and/or chemical mechanism of NO x leading to the typical underestimation of NO x levels in remote MBL by chemical transport models (e.g., Travis et al, 2020). Similarly, the present work reproduces the O 3 level in the South China Sea and Taiwan strait compared to one observation study (in average 21 ppbv) (Lan et al, 2015) but underestimates O 3 compared to other previous measurements (∼50 to ∼85 ppbv; Carmichael et al, 2003;Hatakeyama et al, 2004;Jacob et al, 2003). This could be due to (1) uncertainty in the emission inventories; (2) uncertainty in the initial and boundary conditions; (3) grid size and different spatial range; and (4) a lack of VOC emissions from the ocean (e.g., S. Wang, Hornbrook, et al, 2019).…”

“…We evaluated the simulated air pollutants and halogen species from the three cases with previously reported observations within (or close to) the domain of interest (Table S1). The reported average NO 2 ranges from 30 to 5,300 pptv (Lan et al, 2015;Schreier et al, 2015). The three scenarios also simulate a large concentration range (from pptv to ppbv levels) of NO 2 (see Section 3 for details).…”

Chemical Interactions Between Ship‐Originated Air Pollutants and Ocean‐Emitted Halogens

“…The discrepancy between model and measurements could be due to (1) different period between model and field campaigns; (2) different spatial dimensions and range (a single point in ground campaigns and a 3D line for flight campaigns compared to a 27 × 27 km 2 grid box in the model); (3) uncertainty in the emission inventory from shipping and the islands within the domain; and (4) missing sources and/or chemical mechanism of NO x leading to the typical underestimation of NO x levels in remote MBL by chemical transport models (e.g., Travis et al., 2020). Similarly, the present work reproduces the O 3 level in the South China Sea and Taiwan strait compared to one observation study (in average 21 ppbv) (Lan et al., 2015) but underestimates O 3 compared to other previous measurements (∼50 to ∼85 ppbv; Carmichael et al., 2003; Hatakeyama et al., 2004; Jacob et al., 2003). This could be due to (1) uncertainty in the emission inventories; (2) uncertainty in the initial and boundary conditions; (3) grid size and different spatial range; and (4) a lack of VOC emissions from the ocean (e.g., S. Wang, Hornbrook, et al., 2019).…”

“…We evaluated the simulated air pollutants and halogen species from the three cases with previously reported observations within (or close to) the domain of interest (Table ). The reported average NO 2 ranges from 30 to 5,300 pptv (Lan et al., 2015; Schreier et al., 2015). The three scenarios also simulate a large concentration range (from pptv to ppbv levels) of NO 2 (see Section 3 for details).…”

“…This could be due to (1) uncertainty in the emission inventories; (2) uncertainty in the initial and boundary conditions; (3) grid size and different spatial range; and (4) a lack of VOC emissions from the ocean (e.g., S. Wang, Hornbrook, et al, 2019). WRF-Chem underestimated CO compared to the observations with a range from 145 to 286 ppbv for CO (Carmichael et al, 2003;Jacob et al, 2003;Lan et al, 2015) (Table S1).…”