Semicontinuous PM and black carbon (BC) concentrations, and 24 h integratedPM filter samples were collected near roadways in the KathmanduValley, Nepal. Instruments were carried by a group of volunteer trafficpolice officers in the vicinity of six major roadway intersections in theKathmandu Valley across two sampling periods in 2014. Daily PMfilter samples were analyzed for water-soluble inorganic ions, elementalcarbon (EC) and organic carbon (OC), and 24 elements. Mean PM and BCconcentrations were 124.76 µg m and 16.74 µgC mduring the drier spring sampling period, and 45.92 µg m and13.46 µgC m during monsoonal sampling. Despite the lowermonsoonal PM concentrations, BC and several elements were notsignificantly lower during the monsoon, which indicates an importantcontribution of vehicle-related emissions throughout both seasons in thisregion. During the monsoon, there was an enhanced contribution of chemicalspecies (elements and water-soluble inorganic ions), except secondaryinorganic ions, and BC to PM (crustal elements: 19 %; heavymetals: 5 %; and BC: 39 %) compared to those in spring (crustal elements:9 %; heavy metals: 1 %; and BC: 18 %). Silica, calcium, aluminum, and ironwere the most abundant elements during both spring and the monsoon, withtotal concentrations of 12.13 and 8.85 µg m, respectively.PM and BC showed less spatial variation compared to that forindividual chemical species.
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