Implications of the aerosol size distribution modal structure of trace and major elements on human exposure, inhaled dose and relevance to the PM2.5 and PM10 metrics in a European pollution hotspot urban area

The size distributions of atmospheric aerosol mass and several major and trace elements were studied in an urban area in South Poland. 24 h ambient aerosol samples were collected by means of the thirteen stages Dekati low pressure impactor, in an industrial urban area during summer and winter campaigns in 2007 and 2008. Ambient PM (particulate matter) mass size distribution appeared to have a tri-modal pattern, with a predominant peak in the fine fraction (<1 µm). The elemental mass (EM) size distributions also appeared to have multi-modal structure. Based on the patterns of the mean elemental mass size distributions, the detected elements were classified into three groups. The 1st group (A) contains elements with multimodal size distribution and predominant fine mode, namely: S, Zn, Pb, Br, Sb, As, Cl and Cd. The 2nd group (B) includes elements (Fe and Ca) with a predominant mode in the coarse size range. The 3rd group (C) contains elements with broad size distributions (K, Cr, Mn and Cu); both fine and coarse particles significantly contribute to the total elemental mass concentration. The total and regional inhaled dose of ambient PM and the detected elements in human respiratory tract (RT) was estimated, applying the Multiple Path Dosimetry model (MPPD-V2.11). Overall, the total PM mass deposition fractions in the Head air ways (H), Trachea and Bronchiolar (TB) and Pulmonary alveolar (P) regions were found equal to 0.42, 0.04 and 0.08, respectively. The same dosimetry analysis was applied for each element, taking into account the characteristics of their size distribution patterns. It was found that the highest amount of the elemental masses was deposited in the upper region of the RT. The average elemental mass deposition fractions were 0.35±0.08, 0.77±0.07 and 0.49±0.06 for the elements included in the groups A, B and C, respectively. The mass deposition fractions for the lower region of the RT were: 0.05±0.01 (TB) and 0.09±0.01 (P) for group A, 0.02±0.01 (TB) and 0.05±0.02 (P) for B, and 0.04±0.01 and 0.09±0.02 for C. Additionally, a comparison was performed between the inhaled dose estimated from concentration levels corresponding to the PM2.5 and PM10 mass fractions, when a mean particle size is allocated to the fine and coarse fractions of the aerosol mass, and the inhaled dose calculated from highly resolved mass size distribution of PM and individual trace and major elements. The results revealed that for most elements the total inhaled dose in the TB&P region can be adequately estimated from concentration levels and mean particle size characteristics of either PM10 or PM2.5 size fractions; average absolute difference 13% (6% (A), 41% (B), 11% (C)) and 26% (16% (A), 56% (B), 29% (C)), respectively. Significant deviations may be observed in the estimation of the inhaled dose in the H-region, particularly when calculation is based on PM2.5 concentration levels; average absolute difference 59% (44% (A), 92% (B), 71% (C)).