Comparison of PAH mass emissions and their toxicity-weighted trends in China, 2000–2022

Polycyclic aromatic hydrocarbons (PAHs) emissions are often used as direct evidence for subsequent environmental monitoring, governance, and policy-making. However, the toxicity among individual PAH varies significantly, causing their toxicity-based risk to be overlooked. The analysis revealed that total PAH emissions (E_ΣPAHs) has peaked in 2007 (i.e., 1.1 × 10⁵ t), then declined to 2022 (i.e., 7.4 × 10⁴ t) in China. However, the toxicity-weighted PAH emissions (E_ΣTEQ) has not decreased, because the emissions of high molecular weight PAH (E_ΣHPAHs) with high toxicity has not decreased, although the emissions of low molecular weight PAH (E_ΣLPAHs) with low toxicity has decreased significantly. It was verified that the trend of variation in PAH emissions is comprehensively determined by the decrease in biomass and increase in fossil fuel consumption. The decline in E_ΣLPAHs from biomass burning exceeded emission increases attributable to fossil fuel combustion, driving an overall reduction in total LPAHs post-2007 of China. In contrast, E_ΣHPAHs exhibited temporal variability after 2007, as emission reductions from biomass burning were offset by comparable increases from fossil fuel. Despite efforts to reduce emissions of conventional atmospheric pollutants, E_ΣTEQ have not decreased due to the rising fossil fuel consumption and limited pollution control efficiency on E_ΣHPAHs. The findings addressed the gap between PAH mass emissions and their toxicity-weighted trends, which enabled us to pay attention to the variation of E_ΣTEQ for accurate risk management to any region with shifting PAH source profiles. Moreover, emphasis should be placed on transitioning fossil fuel consumption to clean energy and implementing effective measures to reduce E_ΣHPAHs in flue gas, such as adsorption and degradation.