Biomass burning contribution to PM10 concentration in Rome (Italy): Seasonal, daily and two-hourly variations

The possibility of a relevant contribution of biomass burning for domestic heating to PM in the urban area of Rome was explored. The concentration of levoglucosan was determined for 31 months in Rome and in a nearby peri-urban area. During the cold season it reached several hundreds of ng/m at both sites, with a clear inverse relationship with air temperature. During the summer it remained well below 100 ng/m. Although at the peri-urban station the concentration was about 50% higher than at the urban site, the two seasonal patterns show a very good agreement (R = 0.95), pointing at a main contribution of biomass burning in both areas. Additional information came from the comparison of the 2-h time pattern of levoglucosan and the mixing conditions of the atmosphere, evaluated by monitoring natural radioactivity. During the summer levoglucosan concentration followed the pattern of natural radioactivity, indicating a contribution from many small sources scattered on a wide area (wildfires, barbecues, agricultural fires). During the heating season the activity of a source that switched in the early afternoon and switched off before midnight was highlighted. A 2-h delay between levoglucosan time patterns at the peri-urban and the urban site suggests that biomass burning mainly occurs outside Rome and the combustion products are then transported towards the city centre. Biomass burning contribution to PM was estimated as 12% at the peri-urban site and 6.7% inside the city, with relevant implications for the health of the about 2.800.000 citizens living in the urban area of Rome.