Outdoor radon and traffic load levels as cumulative indicators of PM10 and benzene air pollution

Abstract

A new simple cumulative index, named Critical Index (CI), linearly dependent on traffic load and outdoor 222Rn levels (as related to the air mixing condition) was introduced in order to determine the cumulative effect of traffic and atmospheric dilution on PM10 (particles with aerodynamic diameter < 10 μm) and Benzene concentrations in Milan (Italy) air in the years 2000 and 2001. Benzene, PM10 data were obtained from the public air quality monitoring stations. The traffic load was evaluated by the number of vehicles circulating in a street in the centre of Milan. Outdoor 222Rn measurements were carried out by the authors. Traffic data and mixing layer height (estimated through the outdoor 222Rn air activity) combined in a cumulative index, allowed to demonstrate the correlation of traffic load with high Benzene and PM10 pollution levels without exception. Implications: Through the introduction of a new simple cumulative index that is linearly dependent on traffic load and outdoor radon levels (as related to the air mixing condition), it was possible to ascertain the cumulative effect of traffic and atmospheric dilution on PM10 and benzene concentrations in Milan air in the years 2000 and 2001. The proposed methodology will be used to monitor the situation with data collected 10 yr later, in order to evaluate air quality improvement taking into account the influence of different meteorological conditions of the two periods compared.