The 2003 fire season in Portugal: impacts on air quality

Each summer season wildland forest fires burn a considerable area of south European landscape. Summer 2003 was one of the most severe fire seasons experienced during the last decades in Southern Europe and, due to persistent extreme fire conditions, Portugal suffered the worst forest fire season that the country has faced in the last 23 years, with a total area burned of almost 5 times the average. As a consequence, unusual air pollutants concentrations were registered on several monitoring stations of the Portuguese air quality network. Smoke impacts on air quality and human health can be significant because large amounts of pollutants, like particulate matter (PM), nitrogen oxides (NOx) and carbon monoxide (CO), are emitted to the atmosphere. The main purpose of this work is to estimate the air pollution effects of 2003 fires through the application of the air quality modeling system MM5-CHIMERE over continental Portugal domain, with 10x10 km2 horizontal grid resolution and to evaluate the relationship between forest fire activity and air pollutants concentrations in the atmosphere. Forest fire emissions were estimated based on specific southern European emissions factors, on type of vegetation, area burned and fire behavior, and incorporated in the emission input data of the numerical modeling system. Forest fire emissions during 2003 accounted for a high percentage of the total Portuguese emissions, mainly in what concerns CO (60%) and PM (45%). Results were compared with the baseline scenario estimates (without forest fire emissions) and evaluated against monitoring data. Model results showed a significant performance improvement when forest fires are taken into account. PM10 and O3 exceedances may increase approximately 30% for specific monitoring sites, enhancing the importance and the influence of this type of emissions in the local to regional air quality. Moreover, a statistical analysis was applied for 2003 considering three time periods: annual, June to September and the month of August. Only background air quality stations were considered. The ozone maximum concentrations are highly correlated to the area burned and the number of fires for the month of August ranging from 0.50 to 0.80 and 0.51 to 0.78, respectively, depending on the district. 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.