Impacts of Horizontal Resolution on Global Data Assimilation of Satellite Measurements for Tropospheric Chemistry Analysis. (1st June 2021) - Sekiya, Takashi
Abstract: We present the results from a global 0.56°‐resolution chemical data assimilation that integrates satellite observations of ozone, NO2, CO, HNO3, and SO2 from OMI, GOME‐2, SCIAMACHY, TES, MOPITT, and MLS. The assimilation is based on an ensemble Kalman filter technique and simultaneously optimizes ozone precursor emissions and concentrations of various species. The data assimilation at 0.56° resolution reduced model errors against independent surface, aircraft, and ozonesonde observations, which was larger than at coarser resolutions for many cases. By the data assimilation, surface model errors over major polluted regions were reduced by 33%–75% for NO2 and by 15%–18% for ozone. Agreements against assimilated observations for NO2 were improved using the data assimilation at 0.56° resolution by a factor of 1.5–3 compared to 2.8° resolution over major polluted regions. The estimated global total NO x emission over medium and strong source areas were smaller by 15% at 0.56° resolution than at 2.8° resolution associated with resolving small‐scale transport and chemistry processes, while 2%–26% smaller emissions were found for regional total emissions over Europe, the United States, China, India, and South Africa, with larger differences over megacities such as Los Angeles (−41%). The estimated ship emissions were 5%–7% smaller at 0.56° resolution over the Pacific and Atlantic. The 0.56°‐resolution data assimilation provides globally consistent analyses of the emissions and concentrations on a megacity scale, which benefit studies on air quality and its impact on human health at various spatial scales over different regions of the world. Plain Language Summary: Air pollutants such as nitrogen oxides (NOx) and ozone are important for air quality and climate change. This study demonstrates that global 0.56°‐resolution data assimilation of multiple chemical species from multiple satellites can improve chemical concentrations of numerous key species including NO2 and ozone, which was better than that at coarser resolutions. With the 0.56°‐resolution data assimilation, improved agreements with independent surface, ozonesonde, and aircraft observations were obtained for many cases than at coarser resolutions. Over polluted areas, increasing horizontal resolution substantially impacts upon top‐down NOx emission estimates associated with nonlinear atmospheric transport and chemical processes. The globally consistent analyses of emissions and concentrations on a megacity scale obtained from the 0.56°‐resolution data assimilation would benefit studies on air quality and its impact on human health at various spatial scales over different regions of the world. Key Points: Global 0.56°‐resolution data assimilation system was developed to integrate satellite observations of ozone, NO2, CO, HNO3, and SO2 The developed framework provides globally consistent analyses of emissions and concentrations on a megacity scale The data assimilation at 0.56°‐resolution reduced errors against independent observations, which was larger than at lower resolutions