Inverse modelling of NO<sub><i>x</i></sub> emissions over eastern China: uncertainties due to chemical non-linearity

Abstract

Abstract. Satellite observations of nitrogen dioxide (NO 2 ) have often been used to derive nitrogen oxides (NO x = NO + NO 2 ) emissions. A widely used inversion method was developed by Martin et al. (2003). Refinements of this method were subsequently developed. In the context of this inversion method, we show that the local derivative (of a first-order Taylor expansion) is more appropriate than the "bulk ratio" (ratio of emission to column) used in the original formulation for polluted regions. Using the bulk ratio can lead to biases in regions of high NO x emissions such as eastern China due to chemical non-linearity. Inverse modelling using the local derivative method is applied to both GOME-2 and OMI satellite measurements to estimate anthropogenic NO x emissions over eastern China. Compared with the traditional method using bulk ratio, the local derivative method produces more consistent NO x emission estimates between the inversion results using GOME-2 and OMI measurements. The results also show significant changes in the spatial distribution of NO x emissions, especially over high emission regions of eastern China. We further discuss a potential pitfall of using the difference of two satellite measurements to derive NO x emissions. Our analysis suggests that chemical non-linearity needs to be accounted for and that a careful bias analysis is required in order to use the satellite differential method in inverse modelling of NO x emissions.

Comparison and evaluation of anthropogenic emissions of SO<sub>2</sub> and NO<sub><i>x</i></sub> over China

“…The smearing length is around 50 km over China in summer (assuming wind speed 5 m s −1 , NO 2 lifetime 3 h), comparable to the model grid size, implying weak effects upon the inversion of horizontal mass transport between grids. Compared to the basic mass-balance method described in Martin et al (2003), the FDMB method reduces the errors from nonlinearity of NO x -OH-O 3 chemistry (Gu et al, 2016;Cooper et al, 2017). A unitless scaling factor β was introduced to represent the sensitivity of fractional modeled NO 2 columns to the fractional anthropogenic emission changes for each grid.…”

Reconciling the differences between OMI-based and EPA AQS in situ NO<sub>2</sub> trends

“…Moreover, the results presented here represent an alternative and indirect way to assess the importance of lightning NOx for National Climate Assessment (NCA) analyses 15 described in Koshak et al (2015), and Koshak (2017). Inversion studies (e.g., Zhao and Wang, 2009;Gu et al, 2013Gu et al, , 2014Gu et al, , 2016 will be needed to understand the emission changes corresponding to the OMI tropospheric NO2 VCD trends.…”

“…REAM has widely been used in atmospheric NO2 studies, including vertical transport (Choi et al, 2005;Zhao et al, 2009a;Zhang et al, 2016a), emission inversions (Zhao et al, 2009b;Yang et al, 2011;Gu et al, 2013Gu et al, , 2014Gu et al, , 2016, and regional and seasonal variations (Choi et 20 al., 2008a(Choi et 20 al., , 2008b. The model has a horizontal resolution of 36 km with 30 vertical layers in the troposphere, 5 vertical layers in the stratosphere, and a model top of 10 hpa.…”

“…Tropospheric NO2 is emitted both anthropogenically and naturally (e.g., Gu et al, 2016). Anthropogenic fossil fuel combustions and biomass burnings emit mostly nitrogen monoxide (NO) under high temperature, which is later oxidized by O3 into NO2.…”

Comparison and evaluation of anthropogenic emissions of SO<sub>2</sub> and NO<sub>x over China

“…The smearing length is around 50 km over China in summer (assuming wind speed 5m/s, NO x lifetime 3h), comparable to the model grid size, implying weak effects upon the 30 inversion of horizontal mass transport between grids. Compared to the basic mass-balance method described in Martin et al (2003), the FDMB method reduces the errors from nonlinearity of NO x -OH-O 3 chemistry (Gu et al, 2016;Cooper et al, Atmos. Chem.…”