Diagnosis of pollution events by NOx and CO Emissions calculated by Mass-Conserving Inversion method and composition of PM2.5 in Big City of Energy Rich Northern China

This work used a Mass-Conserving inversion estimate framework based on daily TROPOMI NO₂ and CO columns and observed stack fluxes of large industrial and commercial combustion sources from the continuous emissions monitoring systems (CEMS) to quantify three years of daily-scale, grid-by-grid emissions of NO_x and CO at 0.05°×0.05° over Shanxi Province. This region was selected due to its complex topography, rapid development, and the fact that it currently contributes to more than 25% of China’s total coal production and consumption. For these reasons, the region is also highly representative in terms of rapid changes in the spatial-temporal distribution of emissions found in many different regions of the Global South. The calculated emissions, their ratio, and the day-to-day emissions variability are calculated and explained over four different land-use types: rural, natural, urban, and industrial. It is observed that relatively high NO_x emissions, high NO_x/CO and high NO_x/NO₂ ratios are consistent with known industrial areas; relatively lower NO_x emissions, high NO_x/CO and low NO_x/NO₂ ratio are consistent with known urban aeras. While the time series of both NO_x and CO emissions are found to decrease from 2019-2021 overall, there are some complicated inter- and intra-year variations in the emissions, and such trends are not statistically significant over specific sub-regions. The observed variations include both known and unknown special events, as results of intentional policy changes, properties of the climate, and long-range transport atmospheric events. Combined with the Empirical Orthogonal Functions Principal Components Analysis (EOF), the joint composition of PM_2.5, NO₂, and CO emission in the largest city in Shanxi show further insights. Special festivals and economic events including Chinese New Year are clearly observed. There is also a significant decrease in the NO_x to CO emissions ratio observed in urban and rural areas during the COVID-19 induced lockdowns in 2020, but an obvious increase after first-order lockdown. Specifically, it is observed that while there was a drop from 2019 to 2020 due to the COVID lockdowns, that the lowest emissions levels observed actually were found in 2021. On top of this, there was an observed see-saw effect with further reduction of pollution from large enterprises and poorer control of small sources and residential combustion sources. Finally, a switch in the NO_x to CO emissions ratio is observed to rapidly change for strict control measures were introduced during the 2022 Winter Olympics. Diagnosis of pollution events using emissions of NO_x and CO integrated with detailed PM_2.5 chemical components is successfully attempted for the first time.