Retrieval of Tropospheric Trace Gas Nitrogen Dioxide (NO2) by exploiting 1st South Asia’s NASA Pandora Spectrometer

Abstract

The primary anthropogenic sources of nitrogen oxide emissions are fossil fuel combustion, industrial pollution, and intentional burning. Nitrogen dioxide (NO2) is an atmospheric trace gas necessary for the synthesis of tropospheric ozone, a short-lived climatic pollutant. Short-lived climatic pollutants not only disrupt the natural ecosystem but also have long term drastic atmospheric impacts i.e., global warming. In Pakistan, there is an absence of continuous ground-based monitoring equipment for assessing atmospheric trace gas profiles. In Pakistan, South Asia’s first NASA Pandora Spectrometer is recently deployed at NUST, Islamabad to continuously monitor the atmospheric profile of these trace gases. This study focused on the data retrievals of two ground-based monitors (the Pandora Spectrometer and the Horriba NOx Analyzer) and three satellite-based instruments (OMI, TROPOMI & GEMS). The study is first of its kind in the South Asian region where Pandora NO2 Tropospheric column retrieved from Pandora Spectrometer & validated with in-situ measurements. Analysis of diurnal, weekly, monthly, seasonal cycles of Tropospheric NO2 columns showed the peak values during office opening or closing hours. Weekdays have high values of tropospheric NO2 compared to weekends, and similarly high values during winter & post monsoon season. Furthermore, OMI & TROPOMI satellite only covers the region once a day, but incorporation of GEMS data enhanced the validity of ground based NO2 tropospheric columns which cover the region 6-8 hours a day. Pandora tropospheric NO2 column densities exhibited a correlation of 71 and 77 percent with OMI and TROPOMI, respectively, while Pandora Surface NO2 concentrations were 81% correlated with Horriba NO2 surface concentrations. Data validation of Pandora spectrometer with GEMS showed the highest correlation of 87% with Pandora NO2 tropospheric columns. In addition, meteorological parameters were also analyzed to validate the trends of NO2 observations.