Comparative assessment of the quality of aerosol filters for the analysis of ambient air pollution
Introduction. Atmospheric aerosols contain many carcinogenic and toxic substances, a significant part of which is represented by heavy metals. Traditionally, metal analysis is preceded by air sampling on AFA-HA-20 filters; yet, the lack of regulations on permitted background levels of trace elements in the filter material may limit reliability of measurements. Selection of filters with similar technological parameters can be a way to improve analytical accuracy. Objective: To determine contamination of different types of filters and to establish its effect on the results of spectral analysis of airborne metal concentrations in a large industrial city. Materials and methods: We analyzed unexposed AFA-HA-20 filters and Merck Millipore MF filters (n = 30 each) for the content of 13 heavy metals identified as priority pollutants within the Federal Clean Air Project. To assess the effect of filter contamination on the analytical error, air sampling was performed by exposing Merck Millipore MF filters at mobile monitoring stations in the city of Lipetsk. The filters were then analyzed by inductively coupled plasma mass spectrometry with prior microwave mineralization. Results: Our findings confirm the repeatedly obtained data on metal contents in null AFA-HA-20 filters and indicate significantly lower levels of contamination of unexposed Millipore MF filters made of mixed cellulose ethers. Conclusions: The risk of obtaining false positive and false negative results depends on the level and variability of the content of a particular trace metal in the filter. The AFA-HA-20 type of filters traditionally used for ambient air sampling may itself confound measurement result.