Seasonal dynamics and toxicity of PM-bound PAHs in northernmost European megacity.

Cities are prone to air pollution caused by emissions associated with population activities such as road transport, industry, heating, and residential sector. The concentration and chemical composition of particulate matter (PM) is of particular importance as the parameter of air quality measurements. Concerning impact on urban air quality and hazardous health effects accompanied by the capacity for long-range atmospheric transport, polyromantic hydrocarbons (PAHs) are numbered among priority pollutants in the national and international regulatory activities. Seasonal dynamics and toxicity of PM-bound PAHs in a northern context attract the particular attention.

Sampling and PM₁₀-bound PAHs characterization were carried out in urban background of Moscow megacity, the largest as well as the northernmost megacity in Europe. Composition of 16 PAHs which are numbered in the EPA list of ‘Priority Pollutants’, were considered for three periods: spring (from mid-April to the end of May, when a positive average daily temperature is set in Moscow), autumn (from the end of September to the end of November), and winter (from early December to mid-January, when the average daily temperature reliably drops below zero). The sum of 16 PAHs had ranged over the observation period from 0.4 to 10 ng/m³, with increase of the median concentration from spring and autumn to winter due to the maximum anticyclonic atmospheric circulation and emissions from thermal power plants in winter as well as the transition of PAH from PM to the gas phase with an increase of the temperature in spring. Average PAH toxic equivalent (TEQs) were higher in winter and autumn than those in summer and spring. Increased concentrations for BaA, BaP,BgP, Cry, BbF due to high wind speeds indicate a distant source and a long-range transfer of pollutants. While the presence of maxima of concentrations at medium or low wind speeds can serve as an indication of the proximity of sources, as well as the weakening of atmospheric circulation, which leads to accumulation of pollutants (ANT, PYR, BbF, DiBaA, BLU, PHE, BkF) in the measurement area.

Based on the statistical processing, high (> 0.75) positive correlations for all individual PAHs were obtained in autumn and winter. This indicates the high stability and the absence of significant transformation of PAH due to physical and photochemical reactions. At higher temperature in spring compared to autumn-winter, low correlations for phenanthrene was observed due to evaporation of the lowest molecular weight PAHs could proceed more intensively on the aerosol surface.

This work is supported by the Russian Government, through its grant number 14.W03.31.0002.