Investigating the impact of Haze, Clear and Cloudy Conditions on Nitrogen Dioxide retrieval from MAX-DOAS

Abstract

This study presents measurements of Nitrogen Dioxide (NO2) column densities obtained by using Multi-axis Differential Optical Absorption Spectroscopy (MAX-DOAS) during different meteorological conditions such as haze, cloudy and clear sky. DOAS technique is a remote sensing method to retrieve concentration of various trace gases including novel Nitrogen Dioxide (NO2). It is a criteria pollutant and is of paramount importance due to its role in atmospheric chemistry. It dissociates into other products in the presence of sunlight and is key component of various chemical reactions like ozone formation in troposphere. In this study comparison of different NO2 dSCDs retrieval settings was made to find best NO2 DOAS fit settings. Besides this, effect of hazy, clear and cloudy day on NO2 concentration was explored. Furthermore, settings with different O4 cross-sections were also compared to find the impact on best fit settings during cloudy condition. Comparison between results of different settings for NO2 retrieval, reported in literature, and settings used for this study showed good correlation with R2 > 0.97 (R > 0.98). NO2 mean dSCD obtained during clear, cloudy and hazy conditions were 3.56E+16, 4.15E+16 and 4.01E+16, respectively. The results indicated that NO2 concentration obtained on clear day was less than that of hazy and cloudy days due to larger photo-dissociation noted during clear condition. However, mean dSCDs in cloudy and hazy days were slightly higher as less or diffused sunlight was available in these conditions. This study further emphasized on validation of max DOAS observations with OMI satellite observations.