Relationship between Lightning Activity and Tropospheric Nitrogen Dioxide and the Estimation of Lightning-produced Nitrogen Oxides over China

To better understand the relationship between lightning activity and nitrogen oxides （NOx） in the troposphere and to estimate lightning-produced NOx （LNOx） production in China more precisely, spatial and temporal distributions of vertical column densities of tropospheric nitrogen dioxide （NO2 VCDs） and lightning activity were analyzed using satellite measure- ments. The results showed that the spatial distribution of lightning activity is greater in the east than in the west of China, as with NO2 VCDs. However, the seasonal and annual variation between lightning and NO2 density show different trends in the east and west. The central Tibetan Plateau is sparsely populated without modem industry, and NO2 VCDs across the plateau are barely affected by anthropogenic sources. The plateau is an ideal area to study LNOx. By analyzing 15 years of satellite data from that region, it was found that lightning density is in strong agreement with annual, spatial and seasonal variations of NO2 VCDs, with a correlation coefficient of 0.79 from the linear fit. Combining Beirle＇s method and the linear fit equation, LNOx production in the Chinese interior was determined to be 0.07 （0.02-0.27） TgN yr-1 for 1997-2012, within the range of 0.016-0.384 TgN yr-1 from previous estimates.

Observation of tropospheric NO_2 by airborne multi-axis differential optical absorption spectroscopy in the Pearl River Delta region,south China

An airborne multi-axis differential optical absorption spectroscopic （AMAX-DOAS） instrument was developed and applied to measure tropospheric NO2 in the Pearl River Delta region in the south of China. By combining the measurements in nadir and zenith directions and analyzing the UV and visible spectral region using the DOAS method, information about tropospheric NO2 vertical columns was obtained. Strong tropospheric NO2 signals were detected when flying over heavilly polluted regions and point sources like plants. The AMAX-DOAS results were compared with ground-based MAX-DOAS observations in the southwest of Zhuhai city using the same parameters for radiative transport calculations. The difference in vertical column data between the two instruments is about 8%. Our data were also compared with those from OMI and fair agreement was obtained with a correlation coefficient R of 0.61. The difference between the two instruments can be attributed to the different spatial resolution and the temporal mismatch during the measurements.

Year-round changes in tropospheric nitrogen dioxide caused by COVID-19 in China using satellite observation

The lockdown policy deals a severe blow to the economy and greatly reduces the nitrogen oxides(NOx)emission in China when the coronavirus 2019 spreads widely in early 2020.Here we use satellite observations from Tropospheric Monitoring Instrument to study the year-round variation of the nitrogen dioxide(NO_(2))tropospheric vertical column density(TVCD)in 2020.The NO_(2)TVCD reveals a sharp drop,followed by small fluctuations and then a strong rebound when compared to 2019.By the end of 2020,the annual average NO_(2)TVCD declines by only 3.4%in Chinamainland,much less than the reduction of 24.1%in the lockdown period.On the basis of quantitative analysis,we find the rebound of NO_(2)TVCD is mainly caused by the rapid recovery of economy especially in the fourth quarter,when contribution of industry and power plant on NO_(2)TVCD continues to rise.This revenge bounce of NO_(2)indicates the emission reduction of NOx in lockdown period is basically offset by the recovery of economy,revealing the fact that China’s economic development and NOx emissions are still not decoupled.More efforts are still required to stimulate low-pollution development.