An assessment of the spatiotemporal dynamics and seasonal trends in NO₂ concentrations across India using advanced statistical analysis

Abstract

Increasing industrialization and urbanization pose significant risks to air quality and public health. It increases the necessity of a comprehensive understanding of air pollution dynamics. Further, prior research fails to explain detailed variability with levels of the seasonal trends of the pollutants over the years. This study aims to analyze the spatiotemporal variation of NO₂ concentrations across India from 2019 to 2023, focusing on understanding spatial continuity, seasonal trends, and dominant temporal patterns. The processed Sentinel-5P satellite data, which is spatially averaged over grids, was used in the study to enhance map accuracy. Various statistical parameters were used for spatiotemporal assessment. The consistency of NO₂ pollutants distribution over time was analyzed using Global Moran's Index. Further, moving average and cubic spline smoothing techniques were applied to assess the seasonality behaviour. Fast Fourier Transformation (FFT) was used to determine the dominant frequency cycles within the time series data of NO₂ pollutants. The result shows a significant increase in NO₂ levels from 0.7053∗10⁻⁴ mol/sq.m. in 2019 to 0.9634∗10⁻⁴ mol/sq.m. in 2023. Correspondence analysis showed consistent and shifting pollution patterns with spatial associations ranging from 0.6401 to 0.7072. The seasonal fluctuations in NO₂ concentrations represent peaks during pre-monsoon and fall in winter. Further, FFT analysis shows dominant seasonal patterns, a frequency of 0.0833, with an amplitude of 0.3209, depicting strong yearly variations. However, smaller semi-annual and quarterly fluctuations are also observed with amplitude of 0.1402 and 0.0530, respectively. Overall, this paper provides valuable insights into the spatiotemporal distribution of NO₂ pollutants that can be utilized in effective planning of air quality management and targeted pollution control strategies for mitigating the health impacts of pollution.