Temporal and spatial variations of carbon monoxide over the western part of the Pacific Ocean

Abstract

Systematic observations of atmospheric carbon monoxide (CO) have been carried out in the western part of the Pacific Ocean since February 1990. The average CO concentration showed a latitudinal gradient, with higher values in the northern hemisphere than in the southern hemisphere. A clear seasonal CO cycle was found nearly at all sampling locations, showing maximum and minimum concentrations in spring and summer, respectively. In the 30°–35°N latitude zone, the average CO concentration was higher and the seasonal amplitude was larger compared with other latitudes. The CO concentration also showed a large interannual variability mainly in association with forest fires. In particular, the forest fires in Siberia in 1998 and Indonesia in 1997–1998 contributed to a remarkable increase in the regional CO concentration, followed by a recovery that took several months to a year. A three‐dimensional atmospheric global chemical transport model (CHASER) was used to simulate the observed characteristics of the latitudinal distribution, seasonal cycle, and interannual variability relatively well. Tagged CO experiments with the model revealed that the contribution of CO emissions from various regions in the northern hemisphere to the CO concentrations at our sampling locations varied seasonally in association with Asian outflows and long‐range transport from Europe and North America. In the southern hemisphere, biomass burnings significantly affected the regional seasonal CO cycle, in addition to the effect of CO oxidation with OH. It was also found that CHASER underestimates the average CO concentration in the northern hemisphere and its interannual variability.