Spatiotemporal Analysis of Ozone Concentration Trends in Tehran Using Ground-Based and AIRS Satellite Data

Document Type : Original Article

Authors

Amirkabir University of Technology (Tehran Polytechnic)

10.22034/envj.2025.537994.1533
Abstract
Air pollution is considered as one of the most significant environmental challenges resulting from unsustainable urban development, with profound adverse economic and public health impacts. The economic burdens include increased healthcare costs, reduced labor productivity, and damage to agricultural crops, while health effects range from respiratory diseases to cardiovascular problems and premature mortality. The World Health Organization (WHO) reports that 99% of the global population breathes air exceeding WHO pollution guidelines, particularly affecting low- and middle-income countries. Effective air pollution management fundamentally relies on comprehensive air quality monitoring data, which serves as the critical and first step in air pollution mitigation plans, tracking spatial distribution patterns, and analyzing temporal variations. Beyond traditional ground-based monitoring methods including air quality monitoring stations, satellite remote sensing has emerged as an indispensable tool for examining pollutant dynamics across metropolitan areas. This study investigates the spatiotemporal trends of ground-level ozone concentrations in Tehran using integrated datasets from both ground-based monitoring stations and satellite observations. The analysis incorporates data from 21 air quality monitoring stations inside the city (belong to Air Quality Control Company-subsidiary of Tehran municipality) spanning 2017 to 2025, supplemented by tropospheric ozone measurements from the AIRS sensor aboard NASA's Aqua satellite. The AIRS dataset was specifically selected for its unique capability to differentiate tropospheric (ground-level) ozone from stratospheric ozone, with satellite-derived concentrations being converted to ground-level equivalents through integration with atmospheric dispersion models. The results reveal several critical patterns in Tehran's ozone pollution. Most notably, the number of unhealthy ozone days has shown a dramatic increase from just one day in 2017 to 39 days in 2025, indicating a concerning upward trend. Diurnal and seasonal variations follow expected photochemical patterns, with peak concentrations occurring during the hours with the highest sunshine radiation (13:00-15:00) and summer months (July and August), directly correlating with maximum solar radiation intensity. These patterns confirm that ozone formation in Tehran is primarily driven by photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs) under strong sunlight conditions Furthermore, a distinct weekend effect has been identified by the weekly trend analysis, where ozone concentrations are consistently 20% higher on weekends compared to weekdays, a phenomenon which shows the NOx saturation state in the most regions inside the city and the high levels of the ratio of nitrogen oxides to volatile organic compounds and consequently prolonging ozone formation in the weekends. Validation analysis of satellite remote sensing data using the data belongs to the air quality monitoring stations demonstrates strong agreement between satellite-derived ozone concentrations and ground-based measurements, with statistical indicators (R² = 0.94, RMSE = 6.2) confirming the reliability of satellite data for areas lacking ground-based monitoring infrastructure. Spatial distribution patterns show the highest ozone concentrations occurring in areas outside the city, influenced by regional transport mechanisms and favorable atmospheric conditions for ozone accumulation due to lower ratio of nitrogen oxides to volatile organic compounds. These findings underscore the necessity for ozone management strategies that address both local emissions and regional contributions for the pollution measures inside the city, while highlighting the value of combined ground-satellite monitoring systems for comprehensive air quality assessment.

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Articles in Press, Accepted Manuscript
Available Online from 05 October 2025