Near-road sampling of PM2. 5, BC, and fine-particle chemical components in Kathmandu Valley, Nepal

Semicontinuous PM 2. 5 and black carbon (BC) concentrations, and 24g h integrated PM 2. 5 filter samples were collected near roadways in the Kathmandu Valley, Nepal. Instruments were carried by a group of volunteer traffic police officers in the vicinity of six major roadway intersections in the Kathmandu Valley across two sampling periods in 2014. Daily PM 2. 5 filter samples were analyzed for water-soluble inorganic ions, elemental carbon (EC) and organic carbon (OC), and 24 elements. Mean PM 2. 5 and BC concentrations were 124.76g μg m-3 and 16.74g μgCg m -3 during the drier spring sampling period, and 45.92g μgg m-3 and 13.46g μgCg m-3 during monsoonal sampling. Despite the lower monsoonal PM 2. 5 concentrations, BC and several elements were not significantly lower during the monsoon, which indicates an important contribution of vehicle-related emissions throughout both seasons in this region. During the monsoon, there was an enhanced contribution of chemical species (elements and water-soluble inorganic ions), except secondary inorganic ions, and BC to PM 2. 5 (crustal elements: 19g %; heavy metals: 5g %; and BC: 39g %) compared to those in spring (crustal elements: 9g %; heavy metals: 1g %; and BC: 18g %). Silica, calcium, aluminum, and iron were the most abundant elements during both spring and the monsoon, with total concentrations of 12.13 and 8.85g μg m -3 , respectively. PM 2. 5 and BC showed less spatial variation compared to that for individual chemical species.