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Athi River, situated in Machakos County, Kenya, occupies a strategically important position approximately 30 kilometers southeast of Nairobi. The town’s geography is defined by its location within the Nairobi Metropolitan Area, experiencing rapid urbanisation and industrial growth. The terrain is relatively flat, part of the larger Kenyan coastal plain, with a gentle slope towards the east. Elevation averages around 1,600 meters above sea level, influencing temperature and atmospheric conditions. The Athi River itself, a vital water source, flows through the area, though its water quality is increasingly impacted by urban runoff and industrial discharge. Surrounding the town are agricultural lands, primarily smallholder farms, alongside expanding industrial zones focused on manufacturing, cement production, and agro-processing. This mix of land use is a key driver of local air quality challenges. The urban-rural gradient is becoming increasingly blurred as Nairobi’s sprawl extends into Athi River. The proximity to the capital creates a complex air pollution dynamic, with pollutants transported from Nairobi adding to locally generated emissions. Dust from unpaved roads and construction sites further contributes to particulate matter concentrations, particularly during the dry seasons. The prevailing winds, generally from the east, can carry pollutants westward towards Nairobi and vice versa, creating a regional pollution corridor.

Athi River experiences a bimodal rainfall pattern, defining its ‘seasons’ as wet and dry. The ‘long rains’ typically occur from March to May, and the ‘short rains’ from October to December. Air quality generally improves during the wet seasons as rainfall effectively washes away particulate matter and suppresses dust. However, increased humidity can also promote the formation of mould and contribute to indoor air pollution. The dry seasons, particularly January-February and June-September, are periods of heightened pollution. The prolonged dryness leads to increased dust resuspension from roads and construction, exacerbated by higher temperatures and lower wind speeds. Temperature inversions, common during the cooler mornings of the dry season, trap pollutants near ground level. Industrial activity remains consistent throughout the year, contributing a baseline level of emissions. November and December, while experiencing some rainfall, often see a surge in economic activity and transport, potentially offsetting the cleansing effects of the rain. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during the dry seasons. Monitoring local conditions and staying indoors on particularly dusty days is advisable. The prevailing easterly winds can sometimes bring in smoke from agricultural burning in surrounding areas, further degrading air quality.