Recent Trends in Criteria Air Pollutants and Black Carbon Over the Western Indo-Gangetic Plain Using Ground-Based and Satellite Observations

Air pollution poses a serious concern to cities and towns across western Uttar Pradesh, India. Therefore, we have examined the dynamics of gaseous and particulate pollutants, as well as meteorological factors and their sources, at four Central Pollution Control Board monitoring sites in Ghaziabad and Meerut. We reported high concentrations of SO₂ (36.83 µg/m³), NO₂ (115.58 µg/m³), and O₃ (92.38 µg/m³) during March, December, and April, respectively. These elevated levels are attributed to anthropogenic aerosols and photochemical oxidation. Conversely, pollution levels dropped significantly during the rainy season, as rainfall helped wash contaminants out of the atmosphere. High levels of PM₁₀, PM_2.5, and Black Carbon (BC) were recorded in November and December, mainly due to biomass burning, temperature inversions, and the shallow boundary layer. Loni and Indirapuram showed high monthly AQI values of 294.27 and 221.64, respectively. We also estimated the SO₂/NO₂ ratio to distinguish between vehicular and non-vehicular emissions. High ratios in May (4.59) and April (3.48) of 2022 indicate a significant contribution from industrial sources. Similarly, high PM_2.5/PM₁₀ ratios (0.7–0.75) imply that fine particulate matter (PM_2.5) is likely from construction activities. During the Post-Monsoon and winter seasons, AQI is strongly influenced by biomass burning (BB), during which we observed elevated BC concentrations higher than 5 µg/m³. Additionally, we identified different aerosol sources using Ångström Exponent and Aerosol Optical Depth. Biomass burning aerosols were dominant throughout the study period. During the post-monsoon season, BB aerosols, along with urban and industrial emissions, were prevalent. The weak correlation between BC and wind speed indicates the contribution from local sources. In the pre-monsoon season, dust and mixed-phase aerosols were prominent, while winter featured high levels of urban and industrial emissions. This study is critical for understanding AQI trends, pollution sources, and their dynamics over the past few years across western Uttar Pradesh.