Effects of Siberian forest fires on air quality in East Asia during May 2003 and its climate implication

In May 2003, intense forest fires occurred over Siberia, which were the largest fires in the past decade. In order to quantify the effects of these fires on regional air quality in East Asia, we used a global chemical transport model (CTM) with a biomass burning emission inventory constrained by satellite. Our focus was mainly on the enhancements of the ozone and aerosol concentrations due to these fires over East Asia. We first evaluated the model extensively by comparing the simulated and the observed ozone and aerosol concentrations at the EANET sites and found that the simulation reproduced the observed variability of those species. However, some discrepancies were found in the model when compared with the MODIS AOD observations. We tested the sensitivity of the model AOD to different injection heights of fire emissions and found that the model with an injection height of 4.5 km was in better agreement with the observations. We then used our model results to quantify the influences of Siberian forest fires on ozone and aerosols concentrations which were computed using the differences between the simulations with and without Siberian forest fire emissions. The peak increases in the surface PM10 and ozone concentrations were up to 90 μg m−3 and 33 ppbv, respectively, over Siberia. In the downwind regions, the increases ranged from 5 to 30 μg m−3 and from 3 to 20 ppbv for PM10 and ozone concentrations, respectively, having an important implication for air quality over East Asia. Finally, we computed the radiative forcing of aerosols and ozone from the Siberian forest fires as a measure of climate impact. Siberian forest fires were found to act mainly as a cooling agent resulting in a negative radiative forcing of −5.8 W m−2 at the surface over East Asia. The value at the TOA was −1.5 W m−2, indicating that a considerable absorption of radiation occurred in the atmosphere. This result implies that the Siberian forest fires may affect the regional climate over East Asia by intensifying atmospheric stability.