Decoding temporal patterns and trends of PM₁₀ pollution over Delhi: a multi-year analysis (2015–2022)

The current study delved into an extensive analysis of multi-year observations on PM₁₀ to have trends at various time scales in Delhi, India. High-resolution ground observations from all 37 monitoring stations from 2015 to 2022 were used. This study used non-parametric generalized additive model (GAM) based smooth-trend and Theil-Sen slope estimator techniques to analyze temporal trends and variations. The long-term PM₁₀ concentration, both in its ambient and de-seasonalized forms, exhibited a statistically significant decreasing trend. An average decrease of − 7.57 [95% confidence interval (CI) − 16.51, 0.18] µg m⁻³ year⁻¹ for ambient PM₁₀ and − 8.45 [95% CI − 11.96, − 5.58] µg m⁻³ year⁻¹ for de-seasonalized PM₁₀ mass concentration was observed. Breaking it down into seasons, we observed significant declines in PM₁₀ concentrations during monsoon (− 10.71 µg m⁻³ year⁻¹, p < 0.1) and post-monsoon (− 7.49 µg m⁻³ year⁻¹, p < 0.001). On the other hand, summer and winter displayed statistically insignificant declining trends of − 5.32 µg m⁻³ year⁻¹ and − 6.06 µg m⁻³ year⁻¹, respectively. Remarkably, all months except March displayed declining PM₁₀ concentrations, suggesting a gradual reduction in particle pollution across the city. Further analysis of PM₁₀ across various wind sectors revealed a consistent decreasing trend in all wind directions. The most substantial decrease was observed from the northwest (− 10.24 µg m⁻³ year⁻¹), while the minimum reduction occurred from the east (− 5.67 µg m⁻³ year⁻¹). Throughout the 8-year study period, the daily average PM₁₀ concentration remained at 228 ± 124 µg m⁻³, ranging from 33 to 819 µg m⁻³. Seasonal variations were apparent, with concentrations during winter, summer, monsoon, and post-monsoon seasons averaging 279 ± 133, 224 ± 117, 135 ± 95, and 323 ± 142 µg m⁻³, respectively. November had the highest and August had the lowest concentration. Weekend PM₁₀ concentration is slightly lower than weekdays. These findings emphasize the need for more stringent government action plans.