Temporal patterns of n-alkanes at traffic exposed and suburban sites in Vienna

Abstract

Temporal and spatial trends of particulate n-alkanes C24-C33 have been investigated at urban-fringe and traffic exposed inner urban sites of a larger European city. The annual average sum of n-alkanes at the four sampling sites ranged from 21 to 31 ngm 3. The urban impact factor was 30% averaged over the year. The seasonal biogenic emissions of the uneven n-alkanes cause a considerable seasonal variation in the distribution pattern of the alkanes in PM10 both in the city and at the suburban sites. The trends in the distribution pattern can be summarized using the odd carbon preference index CPIodd and the plant wax number %WNA, both of which show clear maxima in summer pointing to important biogenic sources of n-alkanes. The biogenic contributions to the total n-alkanes were around 9% in winter (DJF), and 37% in summer (JJA) at the urban-fringe sites. At the inner city sites, the urban impact is dominated by n-alkanes from combustion sources at all seasons. A comparison of two approaches to determine the contribution of the ''plant debris'' source to ambient PM10 indicates two different mechanisms to form atmospheric ''plant debris''. The observed relative contributions of plant debris to PM10 are well in the same range but exhibit differences in the seasonal trend. Considering the different underlying concepts, the agreement of the derived plant debris contributions to PM10 is noteworthy.