Rural residential energy carrier structure and primary PM<sub>2.5</sub> emissions from the Qinghai-Tibet Plateau

Abstract

Solid fuels, including various types of crop residue, wood, animal dung, and coal, are widely used for daily cooking and space heating in many rural households in developing countries, resulting in significant adverse impacts on regional air quality, indoor air quality, and human health. The Qinghai-Tibet Plateau (QTP) region is considered to be one of the areas with the cleanest air in the world; however, due to reliance on solid fuels in the residential sector, and due to lower air pollutant emissions from other sectors like industry and transportation, solid fuel burning has become a main issue affecting energy use and the environment in this area. It has been recognized that local solid fuel burning contributes significantly to regional climate change resulting in increased average ambient temperature and changes in the glaciers in the QTP area. However, information on household fuel use, residential energy carrier data, and air pollutant emissions in this area is very scarce. In the present study, rural household energy use in Tibet and Qinghai provinces were investigated based on a field survey and questionnaires, and primary fine particulate matter (PM2.5) emissions were estimated. Heavy reliance on solid fuels for both daily cooking and space heating was found in the QTP area. The study showed that for daily cooking activity, the time fractions of use of clean energy carriers including gas and electricity were 27% and 8% in rural Tibet and Qinghai provinces, respectively, and the time fractions of use of biomass fuels, mainly woody fuel and animal dung, were 72% and 35%, respectively. Qinghai has high reliance on coal, but Tibet has low use of coal. For space heating demand, only solid fuels were used in these two provinces. Biomass fuels, primarily wood and animal dung, were also the main fuel used to heat animal foods. Total residential fuel consumption was estimated at 3.88 (3.80−3.96 as the interquartile range) and 4.28 (3.28−5.31) million tones in rural Tibet and Qinghai, respectively, including only 1.76 million tons and 663 tons of gas fuels, respectively. The consumed fuels for cooking and heating activities were nearly equal. In rural Tibet, woody fuels and animal dung comprised up to 44% and 53%, respectively, of the total mass of rural residential fuels consumed, while in rural Qinghai, these two fuels contributed to 17% and 37% of the total mass. Annual residential fuel consumption per household was 7.91 and 5.87 tons/household, respectively, equivalent to about 122 and 129 GJ/household. For each fuel type, there was no statistically significant relationship between the consumption amount and the number of persons in the household ( P> 0.05), however, the total residential fuel consumption was positively correlated with the population at the city level ( P 0.001). This suggested that the fuel consumption per household, which reflects the basic need for each family, was similar for households in different cities, although the residential energy carrier structures were significantly different. Because of heavy reliance on traditional solid fuels, the residential sector is a main source of PM2.5. The estimated total emissions associated with the rural residential sector were 32.1 (31.9−33.4 as the inter-quartile range) and 42.7 (33.1−53.7) Gg, respectively, for Tibet and Qinghai provinces. Air pollutant emissions from the Qinghai-Tibet Plateau have obvious impacts on the ecosystem, including, but not limited to, outdoor and indoor air quality, public health, and regional radiative forcing. Relatively small sample size is a limitation of the present study, and in the emission estimation, emission factors were obtained from an existing database, while localized emission factors would be preferable in estimating air pollutant emissions. In future works, it is recommended to address historic changes of residential energy and the driving factors of the transition. Under the urbanization in this area, future field-based surveys and case studies would be valuable in exploring the impacts of urbanization on residential energy use, air pollutant emissions, human health and regional climate change.