On the variability and correlation of surface ozone and carbon monoxide observed in Hong Kong using trajectory and regression analyses

This paper investigates, the variability and correlation of surface ozone (03) and carbon monoxide (CO) observed at Cape D'Aguilar in Hong Kong from 1 January 1994 to 31 December 1995. Statistical analysis shows that the average O-3 and CO mixing ratios during the two years are 32+/-17 ppbv and 305+/-191 ppbv, respectively. The O-3/CO ratio ranges from 0.05 to 0.6 ppbv/ppbv with its frequency peaking at 0.15. The raw dataset is divided into six groups using backward trajectory and cluster analyses. For data assigned to the same trajectory type, three groups are further sorted out based on CO and NOx mixing ratios. The correlation coefficients and slopes of O-3/CO for the 18 groups are calculated using linear regression analysis. Finally, five kinds of air masses with different chemical features are identified: continental background (CB), marine background (MB), regional polluted continental (RPC), perturbed marine (P{*}M), and local polluted (LP) air masses. Further studies indicate that O-3 and CO in the continental and marine background air masses (CB and MB) are positively correlated for the reason that they are well mixed over the long range transport before arriving at the site. The negative correlation between O-3 and CO in air mass LP is believed to be associated with heavy anthropogenic influence, which results from the enhancement by local sources as indicated by high CO and NOx and depletion of O-3 when mixed with fresh emissions. The positive correlation in the perturbed marine air mass P{*}M favors the low photochemical production of O-3. The negative correlation found in the regional polluted continental air mass RPC is different from the observations at Oki Island in Japan due to the more complex O-3 chemistry at Cape D'Aguilar