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<p>Tropospheric formaldehyde (HCHO) serves as an effective tracer of volatile organic compound (VOC) oxidation and provides insight into regional photochemical regimes. In this study, satellite-derived HCHO column densities from the Ozone Monitoring Instrument (OMI) are analysed over the Indian subcontinent for the period 2007–2021 to examine spatial patterns, seasonal variability, long-term trends, and transport-driven enhancements. Seasonal mean HCHO fields are used to identify persistent hotspot regions, while day-to-day variability is evaluated using back-trajectory, residence-time, and potential source contribution function (PSCF) analyses at two hotspot locations in eastern (Nandapura, Odisha) and southern (Kuttampuzha, Kerala) India. The results reveal pronounced spatial and seasonal contrasts in HCHO distribution, with enhanced summer concentrations over forested regions and coastal zones, and reduced wintertime levels. Summer-to-winter HCHO ratios indicate strong biogenic influence across both hotspots, while trend analysis highlights divergent long-term behaviour, with a sustained increase in HCHO at Nandapura and comparatively stable or declining levels at Kuttampuzha. Analysis of the HCHO-NO<sub>x</sub> ratio demonstrates clear regional differences in ozone sensitivity, identifying NO<sub>x</sub>-limited conditions over the Malabar coast and VOC-limited to transitional regimes over eastern India, with distinct seasonal shifts at Nandapura. Trajectory-based diagnostics show that extreme HCHO events at both locations are associated with air masses that experience prolonged residence over emission-rich regions, including forested areas, coastal zones, shipping corridors, and power sector. Our results indicate that residence time within these source regions, rather than transport pathway alone, plays a critical role in determining peak HCHO column enhancements. Overall, this study demonstrates how long-term satellite observations, when combined with transport and chemical regime diagnostics, can be used to disentangle the roles of biogenic emissions, anthropogenic influence, and atmospheric transport in controlling HCHO variability and ozone sensitivity over India.</p>

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Decoupling anthropogenic and biogenic influences in the formation of HCHO over two hotspot regions of India

  • 期刊论文

  • 发表日期：

    2026年5月12日

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  • Priyanshu Malik,
  • Chinmay Mallik

摘要

Tropospheric formaldehyde (HCHO) serves as an effective tracer of volatile organic compound (VOC) oxidation and provides insight into regional photochemical regimes. In this study, satellite-derived HCHO column densities from the Ozone Monitoring Instrument (OMI) are analysed over the Indian subcontinent for the period 2007–2021 to examine spatial patterns, seasonal variability, long-term trends, and transport-driven enhancements. Seasonal mean HCHO fields are used to identify persistent hotspot regions, while day-to-day variability is evaluated using back-trajectory, residence-time, and potential source contribution function (PSCF) analyses at two hotspot locations in eastern (Nandapura, Odisha) and southern (Kuttampuzha, Kerala) India. The results reveal pronounced spatial and seasonal contrasts in HCHO distribution, with enhanced summer concentrations over forested regions and coastal zones, and reduced wintertime levels. Summer-to-winter HCHO ratios indicate strong biogenic influence across both hotspots, while trend analysis highlights divergent long-term behaviour, with a sustained increase in HCHO at Nandapura and comparatively stable or declining levels at Kuttampuzha. Analysis of the HCHO-NOx ratio demonstrates clear regional differences in ozone sensitivity, identifying NOx-limited conditions over the Malabar coast and VOC-limited to transitional regimes over eastern India, with distinct seasonal shifts at Nandapura. Trajectory-based diagnostics show that extreme HCHO events at both locations are associated with air masses that experience prolonged residence over emission-rich regions, including forested areas, coastal zones, shipping corridors, and power sector. Our results indicate that residence time within these source regions, rather than transport pathway alone, plays a critical role in determining peak HCHO column enhancements. Overall, this study demonstrates how long-term satellite observations, when combined with transport and chemical regime diagnostics, can be used to disentangle the roles of biogenic emissions, anthropogenic influence, and atmospheric transport in controlling HCHO variability and ozone sensitivity over India.