Forest fire emissions under climate change: impacts on air quality

Each summer wildland fires burn a considerable area of the south European landscape. Smoke has to be considered as one of the several disturbing effects of forest fires. Its impacts on air quality and human health can be significant, because large amounts of pollutants, like particulate matter (PM), carbon monoxide (CO), volatile organic compounds (VOC) and nitrogen oxides (NOx), are emitted into the atmosphere. The effects of these emissions are felt at different levels: from the contribution to the greenhouse effect to the occurrence of local atmospheric pollution episodes. In a changing climatic scenario forest fires could become an even larger source of air pollutants to the atmosphere. In Portugal, there is a significant correlation between forest fire activity and air pollutants concentrations in the atmosphere. The 1995-2005 period was analysed, at the district level, and significant correlation coefficients were obtained. The daily O3 maximum concentrations are highly correlated to the area burned and number of fires reaching 0.70 and 0.72, respectively. PM10 daily average also presents significant correlation coefficients especially in August. It is clear, from this analysis, that there is a significant correlation between forest fire activity, in Portugal, and air pollutants concentrations in the atmosphere. In this sense, the main purpose of this paper is to evaluate the impact of a climate change scenario on the air quality over Portugal.

Area burned projections for the SRES-A2 climate change scenario suggest substantial increases in several Portuguese districts leading to considerable amounts of pollutants released to the atmosphere. Future forest fire emissions based on projections of area burned and the anthropogenic emissions based on the A2 scenario were calculated. Estimates of CO2, CO, CH4, NMHC, PM2.5, PM10 and NOx emissions point to significant increases in future climate. In particular, the districts of the North and Central of Portugal will register the highest increases on area burned and consequently on forest fires emissions. Moreover, the annual CO2 equivalent emissions derived from forest fires account for 1.27 Mton for the 1980-1990 period and 7.44 Mton in a 2xCO2 scenario. This represents an overall increase of approximately 500%.

The air quality modelling system MM5-CHIMERE, forced by a global climate model, was applied over Portugal, for a reference year (1990) and for the climate change scenario (2100), aiming to understand the impact of forest fire emissions on air quality, under a changing climate. This modelling system was already tested for the 2003 fire season and the impact of forest fire emissions in air quality is evident contributing to higher levels of PM10 and O3 in the atmosphere. The PM10 and O3 excedances may increase approximately 30% due to forest fire emissions . Preliminary results point to an increase of the fire emissions impact on the future air quality over Portugal.