EGU21-13059, updated on 04 Mar 2021
https://doi.org/10.5194/egusphere-egu21-13059
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Seasonal and episodic influence of local meteorology on fine particulate matter at a regional background site in North East India.

Adnan Qadri1, Shahadev Rabha2, Binoy Saikia2, and Tarun Gupta1
Adnan Qadri et al.
  • 1(Department of Civil Engineering and APTL at Centre for Environmental Science and Engineering (CESE)) Indian Institute of Technology Kanpur, Kanpur, India (adnanmq@iitk.ac.in)
  • 2Coal & Energy Group, CSIR-NEIST, Jorhat-785006, Assam, India.

Climatological parameters like wind speed, temperature, boundary layer height facilitate in dispersion and accumulation of aerosols. Stagnant condition of atmosphere promote accumulation while the pollutants are more likely to get dispersed when non stagnation conditions exist. Sparse studies exist to assess the seasonal and episodic impact of stagnant weather conditions on enhancing aerosol formation in the North-East region of India.PM2.5 sampling was carried from January to November 2019 at a regional background site in Jorhat,Assam. Meteorological variables like wind speed, surface ambient temperature and relative humidity were obtained at one-minute resolution from a collocated air weather sensor. Ventilation coefficient was calculated from wind speed and Boundary Layer Height (BLH) ( from ERA5 reanalysis dataset)

Episodic days were identified as those exceeding permissible values of PM2.5 (National Ambient Air Quality Standards) i.e, 60µg/m3. Average wind speed on polluted and non-polluted days was 0.58±0.08 and 0.77 ± 0.17 m/s respectively. The average BLH was lower for the polluted days (243±73) than the non-polluted days (316±79). Pearson corelation coefficient of PM2.5 and wind speeds on polluted days was low (-0.23) compared to the non-polluted days (-0.54).

Wind rose plots reveal a seasonality trend with winter and summer winds being mostly between North East and South South-West while in monsoon and autumn it lies predominantly between SSW and South South-East (from the Bay of Bengal).  The Pearson correlation coefficients between PM2.5 and wind speeds are -0.66, -0.54 and -0.52 (all p <0.01) in winter, summer and autumn, respectively.Low average BLH persists in Winter and autumn . The seasonal maxima of BLH during winter, summer, monsoon and autumn was 847±167m, 932 ± 271m, 871 ±275m and 814 ± 256m, respectively.  Low night-time BLH (≈ 50m) in winter and autumn contributes to higher aerosol loading. The ventilation coefficient reaches its maxima during daytime around noon with summer season having the maximum daytime VC. High VC (≈270m2/s) in summer and monsoon  signify the seasonal effect on the pollutant dispersion and consequent high PM2.5 loading. Statistically significant negative correlations were obtained between PM2.5 and VC in winter and autumn seasons (-0.75 and -0.43).

Wind speeds have a strong correlation with PM2.5 except for the monsoon season and play a major role in aerosol dispersion.During monsoon, weak dependence of PM2.5 with wind speed and ventilation coefficient suggest significance of precipitation  which cause sscavenging of aerosols. Low correlations exist in summer for PM2.5 and VC due to possible interference due to regional transport of aerosols. 5-day backward trajectory analysis suggest  transport of air masses across the Thar desert and Indo Gangetic Plains to the site during the March(summer) suggesting transport of dust across the region.

How to cite: Qadri, A., Rabha, S., Saikia, B., and Gupta, T.: Seasonal and episodic influence of local meteorology on fine particulate matter at a regional background site in North East India., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13059, https://doi.org/10.5194/egusphere-egu21-13059, 2021.