Coal emissions have been decreasing in the U.S. and Europe for the past two decades due to concern over public health and now increasingly over climate change. In contrast, coal emissions in much of Asia have been increasing rapidly.(1, 2)
Air quality impacts of coal use in China and India have received considerable attention.(3-6)
Far less attention has been given to the growing use of coal in Southeast Asia including Indonesia, Vietnam, Thailand, and neighboring countries. Southeast Asia is one of the fastest developing regions in the world; electricity demand in 2035 is projected to increase by 83% from 2011 levels, more than twice the global average.(7)
Accompanying this economic development is population growth. Indonesia alone is projected to increase its population by 67 million people (28%) between 2010 and 2035.(8)
Population migration from rural areas to cities, or “urbanization”, also increases population densities in polluted areas and heightens demand for grid-based electricity produced by power plants; urbanization rates in Southeast Asia are some of the highest globally, and are projected to increase significantly by 2030.(9)
This growing demand for energy is presently expected to be met by coal because of its low cost and domestic abundance.(10)
We show here that the public health consequences would be severe.
Coal combustion emits sulfur dioxide (SO2
) and nitrogen oxides (NOx
), leading to formation of fine particulate matter (PM2.5
, particles less than 2.5 μm in diameter) and ozone. PM2.5
increases the risk of premature mortality from respiratory and cardiovascular disease. It is the most harmful air pollutant to human health worldwide.(11)
Surface ozone is also a major concern for public health and ecosystems.(12, 13)
Emissions of SO2
can vary widely by coal plant depending on the grade of coal combusted, the type of boiler used, and the emission controls in place.(14, 15)
Here we estimate the burden of air pollution disease due to current (2011) and projected (2030) coal use in Southeast Asia and other East Asian countries outside of China and India. Our 2030 projection is for a “coal future” scenario including all plants currently in construction or in the planning stages. The resulting PM2.5 and ozone concentrations are computed with a high-resolution version of the GEOS-Chem global 3-D chemical transport model, and the resulting premature mortalities are estimated using approaches from the health impact assessment literature.
3 Results and Discussion
shows the increases (Δ) in annual mean surface PM2.5
and 6-month averaged daily maximum 1 h ozone in 2011 due to coal emissions for the countries of Table 1
(population-weighted changes in PM2.5
and ozone by country are listed in SI Table S2
). We also show the resulting exposure densities, computed by multiplying by population density, in order to illustrate the spatial distribution of pollution exposure across the region prior to the country-specific health impact assessment. Corresponding figures showing increases from coal emissions in individual countries are in the SI (Figures S1–S2)
. Our PM2.5
calculations assume dry conditions and do not include condensed water, resulting in conservative PM2.5
mass estimates (e.g., assuming 35% relative humidity increases inorganic PM2.5
mass by ∼33% compared to dry conditions). PM2.5
increases are localized over major urban areas and reach 3 μg m–3
over northern Vietnam. Ozone increases are more spread out but again show peaks of 2–5 ppb over urban areas. These urban influences are magnified in the population exposure density panels, which also show large impacts on eastern China caused by transboundary transport of pollution from Southeast Asia. We discuss the influence on China in more detail below. While, as we show, the contribution of Southeast Asian coal plant emissions to regional PM2.5
and ozone air quality is significant, total PM and ozone concentrations in East and Southeast Asia are also heavily influenced by noncoal emission sources such as fires and biofuels.(55)
Since we do not examine these other sectors in our analysis, a direct comparison between observed and modeled PM and ozone concentrations would have limited utility for evaluating the coal-related pollutant changes simulated here. Isolating changes in observed PM and ozone due to Southeast Asian coal plant emissions would be informative, but also extremely difficult given the limited coverage of surface monitoring sites in this region.
Figure 2. Simulated increases (Δ) in surface PM2.5 (μg m–3) and ozone (ppb) in Southeast Asia due to coal pollution in 2011, and associated population exposure density (multiplying the concentration increase by the population density). Coal pollution in 2011 is determined by the difference between a simulation with 2011 emissions and a simulation with zero coal emissions for the countries in Table 1(emissions in other countries are unchanged). Values for PM2.5 are annual means and values for ozone are 1 h daily maxima averaged for the locally determined 6 month high-ozone season. These metrics are used for the premature mortality calculations as described in the text.
shows the same results for 2030. Increases in PM2.5
exceed 11 μg m–3
over Hanoi and reach 5 μg m–3
over Jakarta and much of southern Sumatra. Increases in ozone are as high as 15 ppb over Indonesia and northern Vietnam. Sulfate contributes 56%
of the overall regional increase in PM2.5
, followed by ammonium (18%), nitrate (15%), and primary particulate emission (11%
). From an exposure perspective, sulfate is somewhat less important (38%) while nitrate is more important (29%) due to abundant ammonia from croplands near populated areas, particularly surrounding Hanoi and Ho Chi Minh City in Vietnam and across much of Sumatra and Java in Indonesia.
Figure 3. Same as Figure 2 but for 2030. Pie charts inset show relative contributions of different aerosol types to regional PM2.5 coal pollution.
The population-weighted PM2.5
and ozone increases in Figures 2
, combined with eq 3
, allow us to compute the current and future premature deaths caused by coal emissions. We estimate 19 880 (11 400–28 400) premature deaths in 2011 from coal combustion in the countries of Table 1
, where the numbers in parentheses indicate the uncertainty bounds of the estimates derived from the high and low RR values shown in SI Table S1
. Of these 17 940 are due to PM2.5
and 1940 due to ozone. For comparison, we also estimate premature mortality for 2011 using values from Burnett et al.(56)
(SI Table S3
). We do not evaluate the 2030 results following the Burnett et al.(56)
approach because in this work we do not project emissions for other sectors or countries outside of Table 1
to 2030, and the Burnett et al.(56)
relationships are more sensitive to baseline pollutant concentrations than the ACS functions. Figure 4
shows the breakdown by country and by cause of death (the breakdown shown is for 2030, but percentages for 2011 are almost identical). Most premature deaths are due to ischemic heart disease (6470) and stroke (5970). Mortality is highest in Indonesia (7480 excess deaths per year) followed by Vietnam (4250 excess deaths per year). China incurs the third highest mortality after Indonesia and Vietnam with 3150 excess deaths per year. All excess deaths estimated for China are due to transboundary pollution.
Figure 4. Coal-related mortality due to emissions in Southeast Asia (countries in Table 1). The left panel shows the premature deaths in individual countries. Premature deaths due to 2011 emissions are shown in blue, and increases between 2011 and projected 2030 emissions are shown in red (population-normalized results are shown in Table S4). Deaths due to PM2.5 and ozone are shown separately. The fraction of PM2.5-related mortality by cause is shown in the pie chart as an average for the whole region in 2030 (IHD ≡ ischemic heart disease, COPD ≡ chronic obstructive pulmonary disease). All ozone-related mortality is from respiratory diseases. The right panel shows the 2030 coal-related mortality in each country broken down by contributions from domestic and transboundary sources (see SI Figure S5 for the domestic and transboundary contributions in 2011). Source countries responsible for transboundary pollution are identified in the legend. As computed here, mortality in China and Rest of East Asia (not included in Table 1) is solely from transboundary pollution. The mortality totals in the right panel are the sums of the contributions from the national simulations with vs without coal emissions for the individual countries in Table 1; because of chemical and CRF nonlinearities they may be greater than the mortality totals in the left panels.
By 2030, we project that total regional premature mortality due to coal pollution will be 63 520 excess deaths from PM2.5
and 6140 from ozone, resulting in a total of 69 660 (40 080–126 710) excess deaths per year (Figure 4
; see SI Figure S4
for the relative contributions of projected population growth, urbanization, and baseline health status changes to these estimates). The highest mortality totals again occur in Indonesia (24 400 excess deaths per year), Vietnam (19 220 excess deaths per year), and China (8870 excess deaths per year). Myanmar experiences the fourth-highest mortality in 2030 with 4030 excess deaths per year, reflecting the dramatic increase in emissions projected there (Table 1
The right panel of Figure 4
shows for each country the contributions to 2030 premature mortality from domestic and foreign coal emissions. These were obtained from the national simulation results with vs without coal emissions for individual countries. We find that more than 80% of coal-related mortality in individual countries of Southeast Asia is due to domestic emissions. The exception is Thailand, for which transboundary pollution from nearby Vietnam is larger than the domestic source.
Vietnam is the largest transboundary contributor to 2030 mortality in China, mainly influencing southern China by direct transport of coal PM2.5
. In addition, we see in the right-hand panel of Figure 3
significant population exposure in the densely populated East China Plain. The increase in PM2.5
there is mostly driven by PM2.5
pollution transported from South Korea (SI Figure S1
) and by the increase in ozone, speeding up the rate at which local Chinese SO2
emissions are converted to sulfate and nitrate.
Leibensperger et al.(57)
previously showed that NOx
emissions in the US, Europe, and China cause intercontinental PM2.5
pollution by increasing surface ozone on a hemispheric scale, leading to faster PM2.5
production in downwind continents from the oxidation of locally emitted SO2
, that is, the same effect that we find here on a smaller scale for the East China Plain (Figure 3
). We used the global GEOS-Chem simulation to examine the influence of Southeast Asian coal emissions on other continents but found the effects to be very small. Maximum annual average intercontinental PM2.5
enhancements occur over polluted northern Europe but are less than 0.01 μg m–3
. Peak intercontinental increases in seasonal average daily maximum 1 h surface ozone occur over other tropical continents but are less than 0.5 ppb. Even when normalized to the magnitude of NOx
emissions, intercontinental influence from Southeast Asia on surface PM2.5
in the U.S. and Europe is small compared to that from northern midlatitude continents(57, 58)
because Southeast Asia is out of the westerly midlatitude circulation. On the other hand, seasonal southerly flow from Southeast Asia leads to stronger influence on China as shown in Figure 3
. Intercontinental influence from Southeast Asia on surface pollution in other tropical continents is weak in part because of strong vertical mixing, limiting influence on ozone, and relatively low emissions of SO2
in these other continents, limiting oxidant-mediated influence on PM2.5
There are several limitations to our analysis. First, our analysis only includes one year of meteorology and therefore does not account for interannual variability in meteorological parameters (e.g., precipitation or temperature) that may affect pollutant formation and transport. We also do not account for future changes in climate, which may influence PM2.5
and ozone formation over Asia.(47)
Second, we do not account for potential changes in total PM and ozone concentrations by 2030 due to noncoal plant emissions (e.g., biofuels or residential coal) or future emissions in countries outside Table 1
. Because we use a nonlinear CRF function, assuming different background PM and ozone concentrations for 2030 might lead to different estimates for premature mortality due to coal-related pollution, especially in areas with lower background PM and ozone. Also, our total mortality estimates assume that the PM2.5
– and ozone-related deaths can be added together, which could lead to double counting if the observed influences of PM2.5
and ozone on premature mortality are not independent of each other. However, single pollutant assessments may also underestimate the total disease burden by neglecting the effects of other pollutants that may be present.(59)
Ultimately our results are not significantly sensitive to this assumption since ozone-related mortality represents less than 10% of our total estimate; including only PM2.5
-related mortality still produces an estimate of 64 000 excess deaths annually from Southeast Asian coal pollution by 2030. Lastly, although comparisons vary by cause of death and by country, our total premature mortality estimates are also almost twice as high overall for 2011 compared to estimates produced with the Burnett et al.(56)
relationship, suggesting that the CRFs we use may be biased high compared to other approaches. On the other hand, the PM2.5
estimates we report were calculated assuming dry conditions, possibly underestimating PM2.5
by as much as 30% and offsetting some of the potential overestimate incurred by our choice of CRFs. Additionally, while our total mortality estimates for 2011 are high compared to using the values from Burnett et al.,(56)
our estimate for premature mortality in Indonesia, the country with the most excess deaths overall, is lower by 20%.
In contrast to the global trend toward cleaner fuel, the future of power generation in Southeast Asia is currently projected to rely on coal.(9)
Our analysis shows that the cost to human health of this coal-dominated energy trajectory is severe. We estimate ∼20 000 premature deaths every year due to coal pollution from currently operating power plants in Southeast Asia, with the largest effects in Indonesia and Vietnam. These numbers may increase to ∼70 000 excess deaths per year by 2030 if all currently approved coal plants in Southeast Asia become operational. Beyond Indonesia and Vietnam, the third greatest mortality toll from Southeast Asian coal emissions is in China, where we expect ∼9000 premature deaths annually by 2030. Coal emissions from power plants in China are presently declining,(2, 60)
so that rising transboundary pollution influence from Southeast Asia will likely become of increasing concern if no action is taken to avoid emission increases from that region.
In January 2016, the Vietnam government announced plans to drastically reduce their plans for future coal expansion(61)
citing both climate and air quality concerns. The air quality concerns drew from preliminary accounts of our work presented at news conferences.(62)
Recognition of the public health costs of a coal-based future may guide other countries in Southeast Asia to follow Vietnam’s lead and choose a more sustainable pathway for meeting their energy needs.