Non-Negligible Stack Emissions of Noncriteria Air Pollutants from Coal-Fired Power Plants in China: Condensable Particulate Matter and Sulfur Trioxide

In this study, we investigated the emission characteristics of condensable particulate matter (CPM) and sulfur trioxide (SO₃) simultaneously through ammonia-based/limestone-based wet flue gas desulfurization (WFGD) from four typical coal-fired power plants (CFPPs) by conducting field measurements. Stack emissions of filterable particulate matter (FPM) all meet the Chinese ultralow emission (ULE) standards, whereas CPM concentrations are prominent (even exceed 10 mg/Nm³ from two CFPPs). We find that NH₄⁺ and Cl^- increase markedly through the ammonia-based WFGD, and SO₄^2- is generally the main ionic component, both in CPM and FPM. Notably, the occurrence of elemental Se in FPM and CPM is significantly affected by WFGD. Furthermore, the established chemical profiles in FPM and CPM show a distinct discrepancy. In CPM, the elemental S mainly exists as a sulfate, and the metallic elements of Na, K, Mg, and Ca mainly exist as ionic species. Our results may indicate that not all SO₃ are included in CPM and they co-exist in stack plume. With the substantial reduction of sulfur dioxide (SO₂), S distributed in SO₃, CPM, and FPM becomes non-negligible. Finally, the emission factors of CPM and SO₃ under typical ULE technical routes fall in the ranges of 74.33-167.83 and 48.76-86.30 g/(t of coal) accordingly.