Fig. 3: Anthropogenic substances confirmed in PM2.5.
Examples of environmental contaminants detected across different extracts and modes of analyses, all of which were confirmed by comparison with authentic standards (i.e., identification Level-1). Dashed-line intersections indicate example analytes detected in multiple extracts or modes of analysis. Nonpolar hydrocarbons, including PAHs and oxy-PAHs, were detected in the NPOC extracts by GC-HRMS with electron ionization (EI) and/or by negative chemical ionization (NCI). Sulfur-containing PACs were detected and confirmed by GC-EI, while other persistent pollutants (e.g., PCBs, BDEs) by GC-NCI. The WSOC and POC fractions were analyzed by LC-HRMS with each extract injected twice for separate acquisitions in electrospray positive (ESI+) and negative (ESI−) modes. ESI− is optimal for weak organic acids, while ESI+ reveals nitrogenous bases and a range of polar neutral molecules such as alcohols, aldehydes, and ketones. These analyses combined allowed the detection of anthropogenic pollutants representing a wide variety of chemical classes, some potentially originating from atmospheric oxidation of incomplete combustion sources, others synthesized for commercial or industrial use, e.g., plasticizers, generic biocides, insecticides, herbicides, and their transformation products.
