Large‐scale structure of trace gas and aerosol distributions over the western Pacific Ocean during the Transport and Chemical Evolution Over the Pacific (TRACE‐P) experiment

Abstract

The Models‐3 Community Multiscale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is used to analyze the Asian continental outflow of carbon monoxide (CO), ozone (O₃), and aerosol sulfate (SO₄²⁻) to the western Pacific Ocean during the period 17–24 March 2001. In this time period eight airborne observations (DC‐8 flights 11–14 and P‐3B flights 13–16) of the NASA Transport and Chemical Evolution Over the Pacific (TRACE‐P) mission were being conducted over a broad area covering Hong Kong, Okinawa, the East China Sea, and southern Japan. Comparison of model results with observations shows that the model reproduces the main observed features of CO, O₃, and SO₄²⁻, including horizontal and vertical gradients, of the Asian pollution outflow over the western Pacific. Model results show that the fast boundary outflow from Asia to the western Pacific is largely restricted to the middle latitudes, and the maximum outflow fluxes are in the lower free atmosphere (3–6 km) north of 25°N. Simulations with and without biomass burning emissions are conducted to quantify the impacts of biomass burning on tropospheric concentrations of CO and O₃. Biomass burning is found to contribute more than 50% of the CO concentrations and up to 40% of the O₃ concentrations in the boundary layer over the major source regions. The largest percentage contributions to CO and O₃ levels (up to 40% and 30%, respectively) over the western Pacific are in the lower free troposphere (2–6 km).