MAX-DOAS measurements of tropospheric NO<sub>2</sub> and HCHO in Nanjing and a comparison to ozone monitoring instrument observations

Abstract

Abstract. In this paper, we present long-term observations of atmospheric nitrogen dioxide (NO2) and formaldehyde (HCHO) in Nanjing using a Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument. Ground-based MAX-DOAS measurements were performed from April 2013 to February 2017. The MAX-DOAS measurements of NO2 and HCHO vertical column densities (VCDs) are used to validate ozone monitoring instrument (OMI) satellite observations over Nanjing. The comparison shows that the OMI observations of NO2 correlate well with the MAX-DOAS data with Pearson correlation coefficient (R) of 0.91. However, OMI observations are on average a factor of 3 lower than the MAX-DOAS measurements. Replacing the a priori NO2 profiles by the MAX-DOAS profiles in the OMI NO2 VCD retrieval would increase the OMI NO2 VCDs by ∼30 % with correlation nearly unchanged. The comparison result of MAX-DOAS and OMI observations of HCHO VCD shows a good agreement with R of 0.75 and the slope of the regression line is 0.99. An age-weighted backward-propagation approach is applied to the MAX-DOAS measurements of NO2 and HCHO to reconstruct the spatial distribution of NO2 and HCHO over the Yangtze River Delta during summer and winter time. The reconstructed NO2 fields show a distinct agreement with OMI satellite observations. However, due to the short atmospheric lifetime of HCHO, the backward-propagated HCHO data do not show a strong spatial correlation with the OMI HCHO observations. The result shows that the MAX-DOAS measurements are sensitive to the air pollution transportation in the Yangtze River Delta, indicating the air quality in Nanjing is significantly influenced by regional transportation of air pollutants. The MAX-DOAS data are also used to evaluate the effectiveness of air pollution control measures implemented during the Youth Olympic Games 2014. The MAX-DOAS data show a significant reduction of ambient aerosol, NO2 and HCHO (30 %–50 %) during the Youth Olympic Games. Our results provide a better understanding of the transportation and sources of pollutants over the Yangtze River Delta as well as the effect of emission control measures during large international events, which are important for the future design of air pollution control policies.

Long term MAX-DOAS measurements of NO<sub>2</sub>, HCHO and aerosols and evaluation of corresponding satellite data products over Mohali in the Indo-Gangetic plain

“…The observed NO2 VCDs are comparable to those observed in long term measurements in rural and suburban environments (Kramer et al, 2008;Drosoglou et al, 2017) and satellite observations in the Indian metropolitan city Mumbai (Hilboll et al, 2013). These are much smaller than those observed in the urban areas worldwide (Mendolia et al, 2013;Drosoglou et al, 2017) or rural, suburban and urban locations of China (Ma et al, 2013;Wang et al, 2017a;Chan et al, 2019;Jin et al, 2016;Vlemmix et al, 2015), where the mean monthly levels are generally higher than 1×10 16 molecules cm -2 . The observed seasonal variability of 145% in the 30 days running means can be explained by the seasonality of emissions and the changing lifetimes.…”

“…Due to its simple design, vast applicability for detection of multiple atmospheric constituents, low power demand, minimal maintenance, possible automation and remote access, MAX-DOAS instruments have been extensively employed both for long term monitoring (Ma et al, 2013;Chan et al, 2019;Wang et al, 2017a;Wang et al, 2017b) and extensive fields campaigns (Li et al, 2013;Heckel et al, 2005;Schreier et al, 2020;Halla et al, 2011) over the last decade. These measurements have been used for characterization of pollution and its source attribution , emission strength (Shaiganfar et al, 2017;Shaiganfar et al, 2011), chemistry and transport (MacDonald et al, 2012) and validation of satellite observations (Wang et al, 2017a;Drosoglou et al, 2017;Mendolia et al, 2013).…”

An improved TROPOMI tropospheric HCHO retrieval over China

“…The algorithm is developed based on the optimal estimation method (Rodgers, 2000) and utilizes the radiative transfer model LibRadTran (Emde et al, 2016) as the forward model. In the MAX-DOAS profile retrieval, the lowest 1 km is divided into 10 layers with the thickness of each layer of 100 m, while the thickness of the layers between 1 km and 3 km is set to 200 m. Details of MAX-DOAS HCHO profile retrieval can be found in (Chan et al, 2018;Chan et al, 2019).…”

First observation of tropospheric nitrogen dioxide from the Environmental Trace Gases Monitoring Instrument onboard the GaoFen-5 satellite

“…However, EMI generally underestimates tropospheric NO 2 VCDs by 30% compared to MAX-DOAS. The biases can be explained by the difference in spatial coverage between the ground-based and satellite observations 24,25 . In general, both satellite and ground-based validations of EMI NO 2 measurements show good agreement with correlation coefficients (R) of 0.…”