With a continuous increase of population and in demand for energy, motorization, and industrial and agricultural products, Asia becomes the largest emitter regions of air pollutants and greenhouse gases over the world. Therefore, Asian regions are considered to have a large potential of co-benefit mitigating both air pollution and global warming by reducing anthropogenic emissions. However, the issue is not so simple because some air pollutants such as sulfate, one of major components of PM2.5, are cooling agents whose reductions have effects of warming air temperature. Therefore, it is necessary to assess how reducing emissions affects air quality and temperature and for the purpose, firstly, precise understanding of emission amounts of related species is required. In addition, verification and evaluation of effects of reducing emissions on air pollution and climate change by air quality and climate models are also necessary and long-historical emission inventories including gridded data are essential for the simulations.
Under the backgrounds, in this study, development and improvement of the Regional emission inventory in ASia (REAS) system calculating emissions from any sources, processes and technologies is conducted. The system can be used to evaluate effects of emission control measures, create emissions of any scenarios, and develop gridded data for air quality and climate models. Targets of REASv3.2, current version in 2020, are anthropogenic sources (fuel combustion, industrial process, agriculture, evaporation, etc.) in East, Southeast, and South Asia. REASv3.2 provides emissions of SO2, NOx, CO, NMVOC, NH3, PM10, PM2.5, BC, OC, and CO2 for each country and its sub-regions and also provides monthly gridded data with 0.25° x 0.25°resolution during 1950-2015 (Kurokawa and Ohara, 2020). The REAS system is continuously updated and planed to expand target years, species, and sources.
This study estimated total emissions in Asia averaged during 1950-1955 and 2010-2015 (growth rates in these 60 years estimated from the two averages) as follow: SO2: 3.2 Tg, 42.4 Tg (13.1); NOx: 1.6 TgNO2, 47.3 TgNO2 (29.1); CO: 56.1 Tg, 303 Tg (5.4); NMVOC: 7.0 Tg, 57.8 Tg (8.3); NH3: 8.0 Tg, 31.3 Tg (3.9): CO2: 1.1 Pg, 18.6 Pg (16.5); PM10: 5.9 Tg, 30.2 Tg (5.1): PM2.5: 4.6 Tg, 21.3 Tg (4.6); BC: 0.69 Tg, 3.2 Tg (4.7): OC: 2.5 Tg, 6.6 Tg (2.7). Clearly, all the air pollutant emissions in Asia increased significantly during these six decades. However, situations were different among countries and regions
In recent years, the relative contribution of air pollutant emissions from China was the largest along with rapid increase in economic growth, but most species have reached their peaks and the growth rates of other species have become at least small or almost zero due to introduction of abatement equipment such as flue gas desulfurization (FGD) for SO2 and selective catalytic reduction (SCR) for NOx, and substitution of fuels from coal and biofuels to cleaner ones. On the other hand, air pollutant emissions from India showed an almost continuous increase due to coal combustion in power plants and industry sector, and road transport, which are causing recent serious air pollution problems in India. For countries in Southeast Asia, emissions of air pollutants also generally showed increasing trends along with economic situation and motorization. Trends in Japan were much different than those of the whole of Asia. Emissions increased rapidly along with economic growth during the 1950s-1970s, but those of most species were reduced largely from peak values. In addition, peak years were mostly 40 years ago, reflecting the time series of introduction of control measures to mitigate air pollution. As described above, trends and spatial distribution of air pollutants in Asia are not simple and are becoming complicated.
REAS datasets are utilized by various national and international projects for atmospheric environment. In the model inter-comparison study for Asia (MICS-Asia) Phase III, the MIX inventory (a mosaic Asian anthropogenic emission inventory) was developed to provide reliable emission datasets of Asia to air quality and climate models by harmonizing different local emission inventories with the mosaic approach (Li et al., 2017). REAS was used as the based data in Asian region. The MIX inventory has been incorporated into the official global emission inventory of the Task Force on Hemispheric Transport of Air Pollution (TF HTAP) and utilized by atmospheric science researchers over the world. REAS is also applied to domestic projects of the Ministry of Environment Japan, such as “Investigation and examination of photo-chemical oxidant (H27 (2015) and H28 (2016))”, “Analysis working group for photo-chemical oxidant simulations”, and “Commission for estimating contribution rates of emission sources for PM2.5 (H28 (2016))”.
This study has been supported by the Environmental Research and Technology Fund (grant no. S-7 and no. S-12) of the Ministry of Environment Japan/the Environmental Restoration and Conservation Agency of Japan and the Japan Society for the Promotion of Science, KAKENHI (grant no. 19K12303).
The papers on this study are as follows: