Abstract
Photolysis of glyoxal (CHOCHO) and other volatile organic compounds (VOC) in the presence of NOx results in tropospheric ozone and secondary organic pollutants formation. Glyoxal, with a relatively short lifetime, plays an important role in VOC formation in the planetary boundary layer. This study presents a comparative analysis of CHOCHO retrieval from mini MAX-DOAS observations at two different monitoring sites in Germany and Pakistan. Firstly, CHOCHO differential slant column densities (DSCDs) were retrieved by using differential optical absorption spectroscopy (DOAS) technique during a field campaign called MAD-CAT (Multi Axis DOAS-Comparison Campaign for Aerosols and Trace gases) from 18 June to 17 July 2013 in Mainz, Germany (49.965387°N, 8.242531°E). A second dataset was acquired from 18 June to 17 July 2015 at ground-based measurements taken with mini MAX-DOAS at IESE (Institute of Environmental Sciences and Engineering), NUST (National University of Sciences and Technology) Islamabad (33.6416°N, 72.9835°E), Pakistan. Tropospheric vertical column densities (VCDs) of CHOCHO were derived from measured DSCDs by using geometric air mass factor approach. Results show that CHOCHO emissions from biogenic sources are largely driven by actinic flux. Covariance of ambient temperature and relative humidity was also investigated at both sites. Significant correlation between actinic flux and CHOCHO VCDs (r > 0.8) along with similar diurnal variation was observed at both monitoring sites. Quantitative difference observed in CHOCHO VCDs is primarily triggered by the difference in actinic flux and vegetation profiles of both monitoring sites.
Highlights
An increasing world population is driving rapid urbanization, industrialization, and an increase in transportation
This study presents a comparative analysis of atmospheric CHOCHO monitored during the MAD-CAT (Multi Axis differential optical absorption spectroscopy (DOAS)-Comparison campaign for Aerosols and Trace gases) field campaign from June to July 2013 in Mainz, Germany and at recently-established monitoring site at the Institute of Environmental Sciences and Engineering Islamabad, Pakistan from June to July 2015
The difference observed in diurnal concentrations of CHOCHO vertical column densities (VCDs) over Mainz and Islamabad can be attributed to differences in actinic flux and vegetation cover/type, mainly, and might be influenced by temperature and relative humidity to some extents in both places
Summary
An increasing world population is driving rapid urbanization, industrialization, and an increase in transportation. Many researchers reported OH oxidation as second most critical removal mechanism of atmospheric CHOCHO [3,15]. Various studies reported the atmospheric monitoring of CHOCHO across the globe during the last decade. Field Campaign) field campaign in Mexico City and reported concentrations were up to 1.8 ppbV as second order photochemical products in roadside traffic emissions. Asian region by using LP-DOAS and MAX-DOAS in order to explore CHOCHO and formaldehyde photochemistry over the rainforests. This study presents a comparative analysis of atmospheric CHOCHO monitored during the MAD-CAT (Multi Axis DOAS-Comparison campaign for Aerosols and Trace gases) field campaign from June to July 2013 in Mainz, Germany and at recently-established monitoring site at the Institute of Environmental Sciences and Engineering Islamabad, Pakistan from June to July 2015. Parameters such as solar irradiance, temperature, and humidity on glyoxal concentrations
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