MAX-DOAS and OMI Measurements of Tropospheric NO2 and HCHO over Eastern China

In this paper,we present long term observations of atmospheric nitrogen dioxide(NO2)and formaldehyde(HCHO)in Nanjing using a Multi-AXis Differential Optical Absorption Spectroscopy(MAX-DOAS)instrument.Ground based MAX-DOAS measurements were performed from April 2013 to February 2017.The MAX-DOAS measurements of NO2 and HCHO vertical column densities(VCDs)are used to validate OMI satellite observations over Nanjing.The comparison shows that the OMI observations of NO2 correlate well with the MAX-DOAS data with Pearson correlation coefficient(R)of 0.91.The comparison result of MAX-DOAS and OMI observations of HCHO VCD shows a good agreement with R of 0.75 and the slope of the regression line is 0.99.The age weighted backward propagation approach is applied to the MAX-DOAS measurements of NO2 and HCHO to reconstruct the spatial distribution of NO2 and HCHO over the Yangtze River Delta during summer and winter time.The reconstructed NO2 fields show a distinct agreement with OMI satellite observations.However,due to the short atmospheric lifetime of HCHO,the backward propagated HCHO data does not show a strong spatial correlation with the OMI HCHO observations.The result shows the MAX-DOAS measurements are sensitive to the air pollution transportation in the Yangtze River Delta,indicating the air quality in Nanjing is significantly influenced by regional transportation of air pollutants.