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Assessing the high-resolution PM2.5 measurements over a Central Himalayan site: impact of mountain meteorology and episodic events

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Abstract

The pristine Himalayan region is often influenced by continental and transboundary intrusions of pollutants over the year. Here, for the first time, systematic high-resolution measurements of PM2.5 are made during March 2018–February 2020 at a high-altitude station Manora Peak, Nainital (29.36 N, 79.46 E, 1950 m amsl) in the Central Himalayan region. The annual mean values of PM2.5 are observed to be 18 ± 17 μg m−3 and 14 ± 11 μg m−3 for 2018 and 2019. Seasonal variability consists of peak levels during summer (26 ± 39, 17 ± 25 μg m−3) and the lowest levels during the monsoon (11 ± 12, 10 ± 10 μg m−3). Convergent cross-mapping analysis between meteorological parameters and PM2.5 identified the wind speed (skill factor “ρ”: 0.47), temperature (0.44), and boundary layer height (0.39) as major factors for the frequent poor air quality incidences (88/606 days), exceeding daily limit of 25 μg m−3. Such episodic deterioration of air quality is mainly caused by dust, biomass burning, and daytime enhancements in pollutants during winter. The day-night variation of PM2.5, in conjunction with boundary layer height and zonal/meridional wind cross-section, revealed that distinct transport mechanisms are responsible for pollutants reaching higher altitudes in summer and winter. To decipher the processes, two case studies, each of dust storms (PM2.5: 340 μg m−3) and biomass burning (PM2.5: 110 μg m−3), are presented that highlight the necessity of continuous PM2.5 measurements to be potentially used for regional climate models and pollution mitigation strategies.

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Data availability

The hourly values of boundary layer height are taken from the ERA-5, a fifth-generation ECMWF reanalysis data (Hersbach et al. 2020; Guo et al. 2021) with a spatial resolution of 0.25o × 0.25o (URL: https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-single-levels, last accessed: June 2022). The AOD (dust AOD & total AOD) values are taken from the global reanalysis dataset Copernicus Atmospheric Monitoring Services (CAMS) (Inness et al. 2019) with a spatial resolution of 0.75°×0.75° (URL:https://ads.atmosphere.copernicus.eu/cdsapp#!/dataset/cams-global-reanalysis-eac4?tab=form). The hourly data of PM2.5 and PM10 are taken from Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2 tavg1_2d_aer_Nx) with resolution 0.5° × 0.625° (https://disc.gsfc.nasa.gov/datasets/M2T1NXAER_5.12.4/summary). The HYSPLIT model input variables like wind mixing, layer depth, and pasquil stability category are imported from the Global Data Analysis System (GDAS) (ftp://arlftp.arlhq.noaa.gov/pub/archives/gdas1) with a resolution of 1-deg Weekly files, for every three hours on different pressure surfaces.

Data will be available on request.

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Acknowledgements

This study is supported by the AAKASH project of RIHN, Kyoto, Japan, and the UCOST-funded project at ARIES, Nainital. The authors are grateful to Director ARIES, Nainital, for his valuable support. We also thank the anonymous reviewers for reviewing this manuscript and providing valuable comments and suggestions.

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All the funding sources are acknowledged for this research project.

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Correspondence to Narendra Singh.

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Rawat, V., Singh, N., Singh, J. et al. Assessing the high-resolution PM2.5 measurements over a Central Himalayan site: impact of mountain meteorology and episodic events. Air Qual Atmos Health 17, 51–70 (2024). https://doi.org/10.1007/s11869-023-01429-7

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