Estimating Hourly Nitrogen Oxide Emissions over East Asia from Geostationary Satellite Measurements
Tianyi Xu, Chengxin Zhang, Jingkai Xue, Qihou Hu, Chengzhi Xing, Cheng Liu
Abstract
Bottom-up emission inventories of atmospheric nitrogen oxides (NO x = NO + NO 2 ) are usually limited to annual updates and have large uncertainties. The recent launch of the Geostationary Environmental Monitoring Spectrometer (GEMS) first provides hourly measurements of trace gas pollutants from space, enabling new insights into the diurnal variations in anthropogenic NO x emissions. In this study, we present an improved top-down estimation of NO x emission using GEMS NO 2 observations and characterize the hourly NO x emissions over cities in East Asia. We use the Gaussian model and polynomial fitting to calculate the hourly NO 2 lifetimes for several “point-source” cities and then derive NO x emissions using the flux divergence method. GEMS observations show significant hourly variations in the NO x emissions. Systematic biases in NO x emission estimates are found between the GEMS-based hourly estimations and previous polar-orbiting satellites with a single daily overpass. Compared to using empirically diurnal emission factors, chemical model simulations using GEMS-based NO x emissions substantially reduce the biases with satellite and surface NO 2 measurements (e.g., for Wuhan, the biases decreased by 31%). This study highlights the essential role of geostationary satellite observations in characterizing the emission and chemistry of atmospheric pollutants and informing emission control policies.