Traffic contribution of polycyclic aromatic hydrocarbons in the center of a large city

Abstract

The presence of particulate PAH and other air pollutants (soot, CO, NO, gas NO y , SO 2, particulate metals, sulfate) in the air in a street (60,000 vehicles each day) in Central Copenhagen and in a park area adjacent to the street was investigated. The diurnal variation of PAH was determined. The PAH composition was also determined in the air in a street carrying only diesel buses. The concentrations of benzo(a)pyrene and benzo(e)pyrene (BeP) were 4.4 ± 1.2 and 4.4 ± 0.7 ng m −3 respectively, in the street air and 1.4 ± 0.6 and 1.3 ± 0.3 ng m −3, respectively, in the air in the park area. The investigation covered the winter months, January-March. The winter was mild, with a mean temperature of 2.8°C. The major PAH source in the street was the traffic. In the city park area also traffic was an important source, but not the major one. Applying BeP as PAH indicator, the traffic contribution was estimated to be 80% in the street. The weekdays distribution was as follows: Working days: 90%. Weekends: 60%. In the city park area the traffic contribution was estimated to be 40%. A city traffic PAH emission profile was determined. The street air PAH profile was very close to the city traffic emission profile. The diurnal variation of PAH showed peaks in the morning and afternoon rush hours and lowest concentrations in the night hours and was very close to the diurnal variation of the traffic gases, CO, NO and gas NO y . A method for differentiating between PAH contribution from petrol vehicles and those from diesel vehicles was developed and applied. It was concluded that the PAH contribution from diesel vehicles was about 2 3 of the total PAH traffic contribution. The shift to the application of a lighter diesel fuel in buses appears to have caused a minor decrease in the street air levels of PAH.