Emission inventory of Nepal's air pollutants for effective air quality management

Abstract

Air pollution is a serious issue in Nepal. It has an impact on the environment as well as human health. This study covers three main sectors of air pollution: crop residue open burning (CROB), open burning of municipal solid waste (MSW), and emissions from diesel vehicles. To estimate specific pollutants from various sources, an inventory of emissions factors (EFs) is required.

This study presents a gridded emissions inventory of Nepal's key open burning sectors at a fine resolution of 1 km x 1 km. In 2016/17, the mass of CROB was 2,908 Gg, accounting for 22% of the dry matter produced. The air pollutant emissions were calculated by multiplying the mass of crop residue burned with EFs, which was CO 2 4,140, CO 154, CH 4 6.5, SO 2 1.2, PM 2.5 24.5, OC 8.6, BC 2.2, NO x 7, NMVOC 22.5, and NH 3 2.7 , in Gg/yr. Open burning was more common in districts with less cattle per hectare. The other contributing factors were the use of combine harvesters, especially in the Tarai districts, and labor migration. Rearing more cattle and utilizing dung for clean energy production as well as industrial raw materials could be the mitigation options to reduce CROB. Likewise, the entire quantity of garbage burnt openly in 2011 was estimated to be 89.2 Gg (i.e., 0.24 Gg/day), accounting for 4.5% of all waste generation. By multiplying the mass of waste burnt with EFs, the air pollutant emissions were estimated as PM 2.5 0.67 (OC 0.51), PM 10 0.72, BC 0.3, CO 2 145, CH 4 0.36, SO 2 0.06, NO x 0.23, CO 7.66, NMVOC 1.36, and NH 3 0.07, all in Gg. Lower waste collection efficiency reveals more open burning, especially in the rural areas of Kathmandu Valley and Nepal. MSW open burning could be minimized with proper waste collection services as well as recycling practices.

The emission inventory of diesel vehicle categories was obtained through experimentallybased

EFs for the Kathmandu Valley and Nepal. The fuel-based EFs of CO 2 , CO, BC, and PM 2.5 were calculated using the carbon mass balance technique. In average, the EFs of the diesel vehicles measured while idling (n = 29) were 2,600 for CO 2 , 33.3 for CO, 0.6 for BC, and 5.2 for PM 2.5 , in unit of g/L. In average, the EFs of the diesel vehicles measured while moving (n = 5) were 2,476 for CO 2 , 97.3 for CO, 1.7 for BC, and 20.7 for PM 2.5 , in g/L. In 2017/18, CO 2 was estimated as 2,214-2,781, CO 27.7-88.8, BC 0.513.55

and PM 2.5 3.42-23.47, in Gg, of which 24.4-29.5%, 28.9-32.3%, 12.3-31.9%, and 21.8-42.5% was respectively for the Kathmandu Valley. Higher emission were from lower euro-grade vehicles, including lack of proper maintenance in time, low fuel quality, traffic congestion, and roadway-grade. Implementation of higher grade vehicles (> Euro III/BS III), electric vehicles, better fuel quality with low sulfur, timely repair and maintenance of vehicles, road repair and opting for low-carbon sustainable pathways could significantly reduce air pollution from the transport sector. This study recommends sound policies for open burning and transport sectors that would significantly improve air quality as well as assist in minimizing negative health effects in Nepal.