Dust from northwest India, Pakistan and Arabian Sea main aerosol sources for central Himalayas

This picture has been used for representational purpose

Mineral dust (34 per cent) and biomass burning (27 per cent) are among the main sources of aerosols in the central Himalayan region, a new study has shown. Along with mineral dust and biomass burning, secondary sulphate, secondary nitrate from northwest India and Pakistan, polluted cities such as Delhi, the Thar desert, and the Arabian Sea area, and long-range transported marine mixed aerosols too contribute to the aerosols in the central Himalayas.

This dust transport and forest fires are the main sources of total suspended particles (TSP), particularly in the pre-monsoon period (March-May) when TSP concentration peaks in the region, said the study on source apportionment of atmospheric pollution. The study, which elucidates the atmospheric chemistry, emission source origins, and transport pathways of aerosol over the central Himalayan region, will help the assessment of contributions and temporal variability of sources that influence the area through regional transport as well as climate impacts assessment, a release from the Ministry of Science and Technology said on Thursday.

With a unique role in the Asian climate, the Himalayan region is considered a vulnerable environment. Several chemical speciation studies have been performed for carbonaceous aerosols and inorganic species over the western and central Himalayan regions during the last decade, reporting the dominance of transported aerosol plumes from the Indo-Gangetic plains. However, there is a knowledge gap regarding the primary and secondary organic carbon fractions, along with a lack of statistical methods for identifying and quantifying the sources of air pollutants at a receptor location (receptor model) in the central Indian Himalayas.

In order to address this, researchers at the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, an autonomous research institute under the Department of Science and Technology (DST), government of India, along with Indian and foreign collaborators, studied the chemical composition and source apportionment of total suspended particulate in the central Himalayan region.

The main source regions for aerosols at this remote background location (Nainital) were the plains in northwest India and Pakistan, polluted cities like Delhi, the Thar desert, and the Arabian Sea area. The study revealed that the main aerosol sources (factors) in Nainital were mineral dust (34 per cent), biomass burning (27 per cent), secondary sulphate (20 per cent), secondary nitrate (9 per cent), and long-range transported marine mixed aerosols (10 per cent), exhibiting distinct seasonal patterns.

There was predominance of mineral dust in spring and summer and biomass burning and secondary sulphate in winter. The transported marine mixed aerosol source was mainly associated with SW monsoon air masses during the summer season. The results of the study published in the journal 'Atmosphere' show that carbonaceous aerosols were the maximum in winter due to the intensification of biomass burning over the Indo Gangetic plains and the Himalayas because of domestic heating and shallower mixing layer.

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