Long-term measurements of CO, NO, NO2, benzene, toluene and PM10 at a motorway location in an Austrian valley

Continuous measurements of CO, NO, NO2, PM10, benzene and toluene were conducted over a one-year period at a motorway location in the alpine Inn valley. Diurnal changes in concentrations of detected compounds were observed to vary according to traffic type and frequency, and meteorological conditions of the valley atmosphere, which were both additionally recorded at this location. Seasonal variations were also clearly seen, with lowest levels of compound abundances present in summer and highest levels in winter. Annual mean abundances of compounds were assessed with respect to guideline limits and it was found that NO2 and PM10 exceeded their legislation thresholds. This investigation also included the first continuous year-long measurements of benzene at this location, yielding an annual mean volume mixing ratio of 0.6 ppbV, which is well within the EU guideline limit of 1.5 ppbV. Additionally, benzene abundances were found to correlate well with CO concentrations. A significant correlation was also found between toluene and benzene. However, the ratio toluene:benzene shifted from about 2:1 in summer to approximately 1:1 in winter. This may be explained by a strong evaporative and therefore temperature dependent toluene source, while benzene concentrations mainly result from non-ambient temperature dependent exhaust pipe emissions. This seasonal variation must be taken into account whenever this ratio is used to determine the chemical age of an air mass.