Abstract
Abstract. We present two-dimensional scanning Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations of nitrogen dioxide (NO2) and formaldehyde (HCHO) in Munich. Vertical columns and vertical distribution profiles of aerosol extinction coefficient, NO2 and HCHO are retrieved from the 2D MAX-DOAS observations. The measured surface aerosol extinction coefficients and NO2 mixing ratios derived from the retrieved profiles are compared to in situ monitoring data, and the surface NO2 mixing ratios show a good agreement with in situ monitoring data with a Pearson correlation coefficient (R) of 0.91. The aerosol optical depths (AODs) show good agreement as well (R = 0.80) when compared to sun photometer measurements. Tropospheric vertical column densities (VCDs) of NO2 and HCHO derived from the MAX-DOAS measurements are also used to validate Ozone Monitoring Instrument (OMI) and TROPOspheric Monitoring Instrument (TROPOMI) satellite observations. Monthly averaged data show a good correlation; however, satellite observations are on average 30 % lower than the MAX-DOAS measurements. Furthermore, the MAX-DOAS observations are used to investigate the spatiotemporal characteristic of NO2 and HCHO in Munich. Analysis of the relations between aerosol, NO2 and HCHO shows higher aerosol-to-HCHO ratios in winter, which reflects a longer atmospheric lifetime of secondary aerosol and HCHO during winter. The analysis also suggests that secondary aerosol formation is the major source of these aerosols in Munich.
Highlights
Nitrogen dioxide (NO2) and formaldehyde (HCHO) are important atmospheric constituents that can have a strong influence on air quality and climate
HCHO is an intermediate product of the oxidation of almost all volatile organic compounds (VOCs), which is why it is widely used as an indicator of nonmethane volatile organic compounds (NMVOCs) (Fried et al, 2011)
The air mass factors (AMFs) used in the QA4ECV Ozone Monitoring Instrument (OMI) NO2 product are calculated at 437.5 nm with NO2 vertical profiles taken from the global chemistry transport model TM5-MP (Williams et al, 2017)
Summary
Nitrogen dioxide (NO2) and formaldehyde (HCHO) are important atmospheric constituents that can have a strong influence on air quality and climate Both play a crucial role in the formation of tropospheric ozone (O3) (Crutzen, 1970) and aerosols (Jang and Kamens, 2001), having a strong impact on the Earth’s radiation budget. The NO2 load in many parts of the world including Germany shows decreasing trends, concentrations in many cities in Germany still exceed the World Health Organization (WHO) annual average limit of 40 μg m−3 Such exceedances are recorded at about 40 % of the traffic-oriented monitoring stations (UBA, 2019), constituting one of the most severe air pollution problems in Germany.
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