The impact of fireworks ban relaxation on variations in SO2 emissions in China during the 2023 Chinese New Year

Abstract During the 2023 Chinese New Year (CNY), many city governments relaxed restrictions on residents setting off fireworks. Fireworks contain large amounts of sulfur powder, which releases the toxic air pollutant sulfur dioxide (SO2) when combusted rapidly. In this study, we employed a four-dimensional variational (4DVar) assimilation system to examine variations in SO2 emissions in China by assimilating hourly ground-based observation data. Two sets of experiments were conducted during the CNY in 2022 and 2023 to quantify the variations in SO2 emissions. On CNY's Eve in 2022, nationwide SO2 emissions increased by 4.701 Gg compared to the preceding day. During the CNY in 2023, following the relaxation of the fireworks ban, there was a significant upsurge of 8.22 Gg in SO2 emissions on CNY's Eve compared to the previous day. This increase included a rise of 2.037 Gg in the Energy Golden Triangle region, 1.709 Gg in the North China Plain and 0.945 Gg in northeastern China. After reaching the peak on CNY's Eve, the overall national SO2 emissions during the 2023 CNY showed a rapid decline in the following two days. However, the emission levels remained elevated compared to the pre-CNY period, indicating the lingering effects of fireworks burning. Compared to the forecasts using the prior emissions, the optimized emissions markedly improved the model forecasts of SO2 during the 2023 CNY period, evidenced by an increase in the correlation coefficient (R) from 0.12 to 0.63 and a reduction in the root-mean-square error (RMSE) by 49.9%, demonstrating the effectiveness of the optimized emissions. These findings will be useful for local governments in formulating strategies for fireworks burning during the CNY period.