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Helong, nestled in the eastern part of Jilin Province, China, occupies a geographically significant position within the Changbai Mountains region. Located at coordinates 42.5436°N, 129.0028°E, the city’s terrain is characterised by rolling hills and valleys, a typical landscape of the Northeast Plain. The elevation, averaging around 350 meters, contributes to cooler temperatures and influences local wind patterns. Helong is not directly adjacent to major bodies of water, though the Mudanjiang River flows nearby, impacting regional humidity. The surrounding landscape is a mix of agricultural land – primarily corn and soybean cultivation – and forested areas, typical of the temperate continental climate. The urban-rural gradient is relatively sharp; Helong itself is a compact city, quickly transitioning to agricultural fields and then mountainous terrain. This proximity to agricultural zones introduces potential sources of particulate matter from farming activities, including dust from tilling and burning of crop residue. Furthermore, the city’s location within a basin can exacerbate pollution events by trapping emissions, particularly during periods of stagnant air. Industrial activity, though not dominant, is present in the region, contributing to localised emissions. The prevailing winds, generally from the northwest, can transport pollutants from other industrial centres in Jilin Province, impacting Helong’s air quality.

Helong experiences a distinct seasonal air quality pattern dictated by its temperate continental climate. Spring (March-May) often sees increased dust and particulate matter from agricultural preparation and potential transboundary pollution as winds pick up. Summer (June-August) generally offers the cleanest air, benefiting from monsoon rains that effectively wash pollutants from the atmosphere. However, increased humidity can also contribute to secondary pollutant formation. Autumn (September-November) is a period of concern, as heating demand begins to rise, leading to increased coal combustion for residential and industrial purposes. This, combined with stable atmospheric conditions and temperature inversions, traps pollutants, resulting in poorer air quality. Winter (December-February) is typically the most polluted season. Cold temperatures drive up coal consumption for heating, and frequent temperature inversions prevent vertical mixing of air, concentrating pollutants near the ground. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during autumn and winter. Fog, common in the colder months, can exacerbate respiratory issues by trapping pollutants. Months to favour for outdoor activity are July and August, when rainfall is highest and heating demand is minimal. Monitoring wind direction is crucial, as pollutants can be transported from surrounding areas.