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Shahrīār occupies a distinctive position within the sprawling Tehran metropolitan region of Iran, situated approximately 40 kilometers west of central Tehran at coordinates 35.6531°N, 51.0600°E. This city of over 300,000 residents lies within the southern foothills of the Alborz mountain range, which dramatically shapes its environmental conditions. The terrain slopes gently from north to south, with elevations around 1,200 meters above sea level—significantly lower than Tehran's central districts but still within the elevated plateau that characterizes this region. Shahrīār's location places it within Tehran Province's western agricultural belt, where orchards and farmlands transition into dense urban development, creating a complex urban-rural gradient. The city sits in the Karaj River basin, though it lacks immediate proximity to major water bodies that might moderate its climate. This positioning within the greater Tehran conurbation means Shahrīār experiences air quality profoundly influenced by both local emissions and regional pollution transport. The Alborz mountains to the north act as a partial barrier to atmospheric circulation, particularly during winter when temperature inversions trap pollutants in the valley. Meanwhile, the city's expansion into former agricultural zones has created mixed land use patterns where residential areas intermingle with light industrial operations and transportation corridors. Shahrīār's air quality suffers from its location downwind of Tehran's massive pollution plume during prevailing westerly winds, while also generating its own emissions from urban activities, vehicular traffic, and occasional agricultural burning in surrounding areas.

Shahrīār's air quality follows a distinct seasonal pattern shaped by its continental climate and topographic setting within the Tehran basin. During winter (December-February), pollution reaches its peak as temperature inversions become frequent and persistent—cold air trapped in the valley beneath warmer air aloft prevents vertical mixing, allowing particulate matter and gases to accumulate. These conditions are exacerbated by increased heating emissions and reduced precipitation. Sensitive groups should limit outdoor exertion during these months, particularly on calm, cold mornings when inversion layers are strongest. Spring (March-May) brings gradual improvement as increasing solar radiation breaks up inversion layers and occasional rainfall helps cleanse the atmosphere, though dust storms from western deserts can occasionally degrade air quality. Summer (June-August) typically offers the cleanest air despite high temperatures, as thermal convection creates better vertical mixing and winds from the north provide some ventilation, though ozone levels may rise on hot, sunny days. Autumn (September-November) sees a return to deteriorating conditions as temperatures drop, inversions reestablish, and reduced wind speeds allow pollutants to accumulate—this transitional period often sees rapid declines in air quality as heating season begins. Throughout the year, sensitive individuals including those with respiratory or cardiovascular conditions should monitor daily conditions and plan outdoor activities for midday when mixing is typically best, avoiding early mornings when inversions are strongest and pollution concentrations highest.