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Yima, a prefecture-level city in Henan Province, China, occupies a crucial position within the Taihang Mountains region. Situated at coordinates 34.7469°N, 111.8750°E, the city’s terrain is characterised by a blend of mountainous foothills and the North China Plain. This topography significantly influences air quality, creating natural basins where pollutants can accumulate. Yima’s elevation, averaging around 110 meters, contributes to temperature inversions, trapping emissions near the ground. The city is not directly adjacent to major bodies of water, but relies on regional river systems fed by mountain runoff. Historically, Yima’s development has been heavily linked to coal mining and related industries, forming a substantial industrial belt to the north and west. This concentration of heavy industry is a primary driver of local pollution. The urban-rural gradient is pronounced; the city centre experiences higher concentrations of traffic and industrial emissions, while surrounding agricultural zones contribute to particulate matter from dust and seasonal burning of crop residue. The prevailing winds, often from the northwest during colder months, carry pollutants from these sources towards the city, exacerbating air quality concerns. Understanding this geographic context is vital for addressing Yima’s environmental challenges.

Yima experiences a typical temperate monsoon climate, with distinct seasonal variations in air quality. Winter (November to March) consistently presents the poorest conditions. Low temperatures create stable atmospheric layers, trapping emissions from coal combustion for heating and industrial processes. Reduced wind speeds further hinder dispersion. January and February are particularly challenging. Spring (April-May) sees a gradual improvement as temperatures rise and winds become more frequent, but dust storms originating from the Gobi Desert can temporarily elevate particulate matter. Summer (June-August) generally offers the cleanest air, aided by monsoon rains that effectively wash pollutants from the atmosphere. However, high humidity can contribute to secondary pollutant formation. Autumn (September-October) is a transitional period, with decreasing temperatures and wind speeds leading to a gradual decline in air quality. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor exertion during winter and spring. Monitoring weather forecasts for dust storm warnings is crucial. Avoiding peak traffic hours and industrial areas can also minimise exposure. The interplay of meteorological factors and emission sources dictates Yima’s seasonal air quality patterns.