محیط زیست و توسعه فرابخشی (Jun 2022)
Investigation of Temporal and Spatial Trends of Air Pollutants in the City of Karaj
Abstract
Introduction: One of the significant challenges metropolises faces is air pollution, which has many adverse effects on human health and the environment. Karaj, as an industrial city situated close to the country's major industries and power plants, is severely affected by air pollution from both mobile and stationary sources. The most important study carried out in the field of air pollution in Karaj city can be considered the air pollutant emission inventory of this city, which is stated for criteria pollutants in two categories of stationary and mobile sources, separately for each source.Methodology: After upgrading the air quality monitoring stations in this city, the current study can be considered the first comprehensive study of air pollutants in terms of their temporal and spatial trends. This study measured air quality in stations equipped with the analyzers of four gaseous pollutants, including ozone, carbon monoxide, nitrogen dioxide, and sulfur dioxide, along with two particulate pollutants, including particulates smaller than 2.5 and 10 microns. Furthermore, the city's air quality index, obtained from the total of monitoring stations, was analyzed.Results: The study finds that particulate matter smaller than 2.5 microns and ozone are the main pollutants in Karaj in hot and cold seasons, respectively. The other pollutants exceed the allowable air quality index, rarely. For a period of one-year, particulate matter smaller than 2.5 microns and ozone put the air quality index in the range of unhealthy for sensitive groups and unhealthy for the entire city of Karaj for 94 and 18 days, respectively. Also, this study investigated the pollutant transport effect using the combination of pollutant concentration data, wind speed, and direction. The dominant directions of pollutant transport to that station were determined for each air quality monitoring station. Based on the results of the present study, for PM2.5, as the most critical air pollutant in the city of Karaj, it can be found that the highest concentration and therefore, the most days with the index in the unhealthy range for PM2.5 has been registered in Metro and Zone 3 stations, in the cold seasons of the year (autumn and winter), respectively.Discussion: By examining the location of these two stations, they can be evaluated as traffic stations. Since the Metro station is located in the Karaj metro area, it is not only affected by the pollution caused by the transport fleet on the routes adjacent to the station (the most important of which is the Karaj-Qarvin freeway), but also the traffic and stops of buses and taxi fleets, which can cause the emission of suspended particles in that area. On the other hand, the station of zone 3 is located at a very short distance from Eram Boulevard, which is strongly affected by the pollutants emitted by the transport fleet on this route. Due to the secondary nature of Karaj's main pollutants, such as ozone in the warm season and a high portion of suspended particles smaller than 2.5 microns in the cold season, it is necessary to reduce air pollution through modeling that incorporates photochemical reactions in the atmosphere.
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