Characterization and source apportionment of PM2.5 and PM10 in a Mountain Valley: seasonal variations, morphology, and elemental composition

This study investigates the mass concentrations, morphological characteristics, elemental composition and source apportionment of PM2.5 and PM10 aerosols across different seasons collected in a mountain valley of the central Himalayan region of Uttarakhand, India. The average PM10 concentration was found to be 88.74 +/- 34.12 mu g m<SUP>-3</SUP>, generally below the NAAQS 24-h standard, while the mean PM2.5 concentration was found to be 67.72 +/- 37.00 mu g m<SUP>-3</SUP>, exceeding the NAAQS standard. Elevated PM10 levels during pre-monsoon periods were linked to windblown dust from neighbouring regions and thermodynamic conditions within the planetary boundary layer, while high PM2.5 levels were attributed to temperature inversions and stable atmospheric conditions. The study identified three major particle groups-biogenic, geogenic, and anthropogenic-using SEM-EDX analysis highlighting the significant impact of both natural and anthropogenic sources. Biogenic aerosols were prevalent in the samples. Variations in the composition of the elements are noted, with C and Si being the most predominant. A strong correlation was found between carbon and oxygen (r = 0.926) using Pearson correlation matrix. NOAA HYSPLIT-4 model was used for air mass back trajectory analysis, which suggests that the receptor site station received air mass from both local sources and long-range transport.