Abstract
Formaldehyde (HCHO) and nitrogen dioxide (NO2) concentrations and profiles were retrieved from ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) observation during January 2017 through December 2018 at three sites in Asia: (1) Phimai in Thailand (15.18° N, 102.5° E); (2) Pantnagar (29° N, 78.90° E) in the Indo Gangetic plain (IGP) in India; and (3) Chiba (35.62° N, 140.10° E) in Japan. The NO2 and HCHO partial columns (< 4 km) and profiles simulated using the global chemistry transport model (CTM) and CHASER were compared to those of MAX-DOAS. The vertical sensitivity of the datasets was elucidated using the averaging kernel (AK) information from the MAX-DOAS retrievals. The NO2 and HCHO concentrations at all three sites showed consistent seasonal variation throughout the investigated period. Biomass burning affected the HCHO and NO2 variation in Phimai during the dry season and in Pantnagar during spring (March–May) and the post-monsoon (September–November) season. High NO2 concentrations in Phimai during the wet season (June–September) are attributed to soil emissions of nitrogen oxides (NOx), confirmed from satellite observations and CHASER simulations. Comparison with CHASER shows that the seasonal variations in the HCHO and NO2 abundances at Phimai and Chiba agree well, with a correlation coefficient (R) of 0.80. Results agree with the variation, ranging mainly within the one sigma standard deviation of the observations. At Phimai, pyrogenic emissions contribute to the HCHO and NO2 concentrations up to ~50 and ~35 %, respectively. CHASER showed limited skills in reproducing the NO2 and HCHO variability at Pantnagar. However, the CHASER simulations in the IGP region agreed well with the reported results. Sensitivity studies showed that anthropogenic emissions affected the seasonal variation of NO2 and HCHO concentrations in the IGP region.
Highlights
Formaldehyde (HCHO) is the most abundant carbonyl compound in the atmosphere because it is a high34 yield product of oxidization of all primary volatile organic carbons (VOCs) emitted from natural and anthropogenic sources by hydroxyl radicals (OH)
Results show that CHASER underestimated the NO2 concentration in Chiba, the smoothed 658 CHASER output agrees well with observations
The smoothed CHASER output shows that the RFN values are mostly lower than 1, which is indicative of a VOC limited region, consistent with the observations and the results reported by
Summary
Formaldehyde (HCHO) is the most abundant carbonyl compound in the atmosphere because it is a high yield product of oxidization of all primary volatile organic carbons (VOCs) emitted from natural and anthropogenic sources by hydroxyl radicals (OH). The MAX-DOAS method uses narrowband absorption of the target compounds, thereby obviating radiometric calibration of the instrument Because of these advantages, MAX-DOAS systems are deployed for assessment of aerosol and trace gases in regional and global observational networks such as BREDOM (Wittrock et al, 2004), BIRA-IASB (Clemer et al, 2010), and MADRAS (Kanaya et al, 2014). MAX-DOAS systems are deployed for assessment of aerosol and trace gases in regional and global observational networks such as BREDOM (Wittrock et al, 2004), BIRA-IASB (Clemer et al, 2010), and MADRAS (Kanaya et al, 2014) Such datasets are used in, but are not limited to (1) air quality assessment and monitoring, (2) evaluation of chemistry–transport models (CTMS), and (3) validation of satellite retrieval.
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