Characterization of hydrocarbons in aerosols at a Mediterranean city with a high density of palm groves.

ABSTRACT

Samples of PM1 and PM10 were collected for 1 year at an urban background station in the city of Elche (southeastern Spain) and analyzed to determine the content of n-alkanes and polycyclic aromatic hydrocarbons (PAHs). A few samples were also gathered at a second sampling point established at one of the several palm tree gardens of the city in order to evaluate the influence of biogenic emissions on the urban levels of n-alkanes. Diagnostic parameters obtained for aliphatic hydrocarbons (carbon maximum number (C max), carbon preference index (CPI), and wax n-alkane content (%WNA)) revealed a higher contribution of biogenic n-alkanes in PM10 than in PM1. Moreover, the values of %WNA indicated that the levels of n-alkanes in Elche were more affected by emissions from terrestrial vegetation than in other urban areas, particularly in the palm tree grove location (%WNA = 29 for PM10). PAH diagnostic ratios pointed to traffic as the main anthropogenic source of hydrocarbons in Elche, with predominance of diesel versus gasoline vehicle emissions. The average levels of total PAHs (~1 ng m(-3)) were noticeably lower than the values registered at other urban areas in Europe, most likely because emissions from other sources are scarce. Both aliphatic and aromatic hydrocarbons showed higher levels in the cold season due to the lower atmospheric dispersion conditions, the increase in traffic exhaust emissions, and the lower ambient temperatures that reduce the evaporation of semivolatile species.