空气污染、温室气体与气候

Direct emissions of air pollutants from the cement industry in China were estimated by developing a technology-based methodology using information on the proportion of cement produced from different types of kilns and the emission standards for the Chinese cement industry. Historical emissions of sulfur dioxide (SO₂), nitrogen oxides (NO_X), carbon monoxide (CO), particulate matter (PM) and carbon dioxide (CO₂) were estimated for the years 1990–2008, and future emissions were projected up to 2020 based on current energy-related and emission control policies. Compared with the historical high (4.36 Tg of PM_2.5, 7.16 Tg of PM₁₀ and 10.44 Tg of TSP in 1997), PM emissions are predicted to drop substantially by 2020, despite the expected tripling of cement production. Certain other air pollutant emissions, such as CO and SO₂, are also predicted to decrease with the progressive closure of shaft kilns. NO_X emissions, however, could increase because of the promotion of precalciner kilns and the rapid increase of cement production. CO₂ emissions from the cement industry account for approximately one eighth of China’s national CO₂ emissions. Our analysis indicates that it is possible to reduce CO₂ emissions from this industry by approximately 12.8% if advanced energy-related technologies are implemented. These technologies will bring co-benefits in reducing other air pollutants as well.

Policies to control emissions of criteria pollutants in China may have conflicting impacts on public health, soil acidification, and climate. Two scenarios for 2020, a base case without anticipated control measures and a more realistic case including such controls, are evaluated to quantify the effects of the policies on emissions and resulting environmental outcomes. Large benefits to public health can be expected from the controls, attributed mainly to reduced emissions of primary PM and gaseous PM precursors, and thus lower ambient concentrations of PM_2.5. Approximately 4% of all-cause mortality in the country can be avoided (95% confidence interval: 1–7%), particularly in eastern and north-central China, regions with large population densities and high levels of PM_2.5. Surface ozone levels, however, are estimated to increase in parts of those regions, despite NO_X reductions. This implies VOC-limited conditions. Even with significant reduction of SO₂ and NO_X emissions, the controls will not significantly mitigate risks of soil acidification, judged by the exceedance levels of critical load (CL). This is due to the decrease in primary PM emissions, with the consequent reduction in deposition of alkaline base cations. Compared to 2005, even larger CL exceedances are found for both scenarios in 2020, implying that PM control may negate any recovery from soil acidification due to SO₂ reductions. Noting large uncertainties, current polices to control emissions of criteria pollutants in China will not reduce climate warming, since controlling SO₂ emissions also reduces reflective secondary aerosols. Black carbon emission is an important source of uncertainty concerning the effects of Chinese control policies on global temperature change. Given these conflicts, greater consideration should be paid to reconciling varied environmental objectives, and emission control strategies should target not only criteria pollutants but also species such as VOCs and CO₂.

An inventory of anthropogenic primary aerosol
emissions in China was developed for 1990–2005 using a
technology-based approach. Taking into account changes
in the technology penetration within industry sectors and
improvements in emission controls driven by stricter emission
standards, a dynamic methodology was derived and implemented
to estimate inter-annual emission factors. Emission
factors of PM2.5 decreased by 7%–69% from 1990 to
2005 in different industry sectors of China, and emission factors
of TSP decreased by 18%–80% as well, with the measures
of controlling PM emissions implemented. As a result,
emissions of PM2.5 and TSP in 2005 were 11.0 Tg and
29.7 Tg, respectively, less than what they would have been
without the adoption of these measures. Emissions of PM2.5,
PM10 and TSP presented similar trends: they increased in
the first six years of 1990s and decreased until 2000, then
increased again in the following years. Emissions of TSP
peaked (35.5 Tg) in 1996, while the peak of PM10 (18.8 Tg)
and PM2.5 (12.7 Tg) emissions occurred in 2005. Although
various emission trends were identified across sectors, the cement
industry and biofuel combustion in the residential sector
were consistently the largest sources of PM2.5 emissions,
accounting for 53%–62% of emissions over the study period.
The non-metallic mineral product industry, including the cement,
lime and brick industries, accounted for 54%–63% of
national TSP emissions. There were no significant trends of
BC and OC emissions until 2000, but the increase after 2000
Correspondence to: K. B. He
(hekb@tsinghua.edu.cn)
brought the peaks of BC (1.51 Tg) and OC (3.19 Tg) emissions
in 2005. Although significant improvements in the estimation
of primary aerosols are presented here, there still
exist large uncertainties. More accurate and detailed activity
information and emission factors based on local tests are essential
to further improve emission estimates, this especially
being so for the brick and coke industries, as well as for coalburning
stoves and biofuel usage in the residential sector.

The uncertainties of a national, bottom-up inventory
of Chinese emissions of anthropogenic SO2, NOx, and
particulate matter (PM) of different size classes and carbonaceous
species are comprehensively quantified, for the first
time, using Monte Carlo simulation. The inventory is structured
by seven dominant sectors: coal-fired electric power,
cement, iron and steel, other industry (boiler combustion),
other industry (non-combustion processes), transportation,
and residential. For each parameter related to emission factors
or activity-level calculations, the uncertainties, represented
as probability distributions, are either statistically fitted
using results of domestic field tests or, when these are
lacking, estimated based on foreign or other domestic data.
The uncertainties (i.e., 95% confidence intervals around the
central estimates) of Chinese emissions of SO2, NOx, total
PM, PM10, PM2.5, black carbon (BC), and organic carbon
(OC) in 2005 are estimated to be −14%13%, −13%37%,
−11%38%, −14%45%, −17%54%, −25%136%,
and −40%121%, respectively. Variations at activity levels
(e.g., energy consumption or industrial production) are
not the main source of emission uncertainties. Due to narrow
classification of source types, large sample sizes, and
relatively high data quality, the coal-fired power sector is estimated
to have the smallest emission uncertainties for all
species except BC and OC. Due to poorer source classifications
and a wider range of estimated emission factors,
considerable uncertainties of NOx and PM emissions from
cement production and boiler combustion in other industries
are found. The probability distributions of emission
factors for biomass burning, the largest source of BC and
OC, are fitted based on very limited domestic field measurements,
and special caution should thus be taken interpreting
these emission uncertainties. Although Monte Carlo simulation
yields narrowed estimates of uncertainties compared
to previous bottom-up emission studies, the results are not
always consistent with those derived from satellite observations.
The results thus represent an incremental research
advance; while the analysis provides current estimates of
uncertainty to researchers investigating Chinese and global
atmospheric transport and chemistry, it also identifies specific
needs in data collection and analysis to improve on
them. Strengthened quantification of emissions of the included
species and other, closely associated ones – notably
CO2, generated largely by the same processes and thus subject
to many of the same parameter uncertainties – is essential
not only for science but for the design of policies to redress
critical atmospheric environmental hazards at local, regional,
and global scales.

China’s strategies to control acidifying pollutants and particulate matter (PM) may be in conflict for soil acidification abatement. Acidifying pollutant emissions are estimated for 2005 and 2020 with anticipated control policies. PM emissions including base cations (BCs) are evaluated with two scenarios, a base case applying existing policy to 2020, and a control case including anticipated tightened measures. Depositions of sulfur (S), nitrogen (N) and BCs are simulated and their acidification risks are evaluated with critical load (CL). In 2005, the area exceeding CL covered 15.6% of mainland China, with total exceedance of 2.2 Mt S. These values decrease in the base scenario 2020, implying partial recovery from acidification. Under more realistic PM control, the respective estimates are 17.9% and 2.4 Mt S, indicating increased acidification risks due to abatement of acid-neutralizing BCs. China’s anthropogenic PM abatement will have potentially stronger chemical implications for acidification than developed countries.

Although China has surpassed the United States as the world’s largest carbon dioxide emitter, in situ measurements of atmospheric CO2 have been sparse in China.
This paper analyzes hourly CO2 and its correlation with CO at Miyun, a rural site near Beijing, over a period of 51 months (Dec 2004 through Feb 2009). The CO2-CO correlation analysis evaluated separately for each hour of the day provides useful information with statistical significance even in the growing season. We found that the intercept, representing the initial condition imposed by global distribution of CO2 with influence of photosynthesis and respiration, exhibits diurnal cycles differing by season. The background CO2 (CO2,b) derived from Miyun observations is comparable to CO2 observed at a Mongolian background station to the northwest.  Annual growth of overall mean CO2 at Miyun is estimated at 2.7 ppm yr−1 while that of CO2,b is only 1.7 ppm yr−1 similar to the mean growth rate at northern mid-latitude background stations. This suggests a relatively faster increase in the regional CO2 sources in China than the global average, consistent with bottom-up studies of CO2 emissions. For air masses with trajectories through the northern China boundary layer, mean winter CO2/CO correlation slopes (dCO2/dCO) increased by 2.8±0.9 ppmv/ppmv or 11% from 2005–2006 to 2007–2008, with CO2 increasing by 1.8 ppmv. The increase in dCO2/dCO indicates improvement in overall combustion efficiency over northern China after winter 2007, attributed to pollution reduction measures associated with the 2008 Beijing Olympics. The observed CO2/CO ratio at Miyun is
25% higher than the bottom-up CO2/CO emission ratio, suggesting a contribution of respired CO2 from urban residents as well as agricultural soils and livestock in the observations and uncertainty in the emission estimates. 

A new methodology is developed to constrain
Chinese anthropogenic emissions of nitrogen oxides (NOx)
from four major sectors (industry, power plants, mobile and
residential) in July 2008. It combines tropospheric NO2 column
retrievals from GOME-2 and OMI, taking advantage
of their different passing time over China (10:00 a.m. LT
(local time) versus 02:00 p.m.) and consistent retrieval algorithms.
The approach is based on the difference of NOx
columns at the overpass times of the two instruments; it thus
is less susceptible to the likely systematic errors embedded
in individual retrievals that are consistent with each other.
Also, it explicitly accounts for diurnal variations and uncertainties
of NOx emissions for individual sources. Our best
top-down estimate suggests a national budget of 6.8 TgN/yr
(5.5 TgN/yr for East China), close to the a priori bottom-up
emission estimate from the INTEX-B mission for the year of
2006. The top-down emissions are lower than the a priori
near Beijing, in the northeastern provinces and along the east
coast; yet they exceed the a priori over many inland regions.
Systematic errors in satellite retrievals are estimated to lead
to underestimation of top-down emissions by at most 17%
(most likely 10%). Effects of other factors on the top-down
estimate are typically less than 15% each, including lightning,
soil emissions, mixing in planetary boundary layer, anthropogenic
emissions of carbon monoxide and volatile organic
compounds, magnitude of a priori emissions, assumptions
on emission diurnal variations, and uncertainties in the
four sectors. The a posteriori emission budget is 5.7 TgN/yr
for East China.

Field measurements and data investigations were conducted for developing an emission factor database for inventories of atmospheric pollutants from Chinese coal-fired power plants. Gaseous pollutants and particulate matter (PM) of different size fractions were measured using a gas analyzer and an electric low-pressure impactor (ELPI), respectively, for ten units in eight coal-fired power plants across the country. Combining results of field tests and literature surveys, emission factors with 95% confidence intervals (CIs) were calculated by boiler type, fuel quality, and emission control devices using bootstrap and Monte Carlo simulations. The emission factor of uncontrolled SO₂ from pulverized combustion (PC) boilers burning bituminous or anthracite coal was estimated to be 18.0S kg t⁻¹ (i.e., 18.0 × the percentage sulfur content of coal, S) with a 95% CI of 17.2S–18.5S. NO_X emission factors for pulverized-coal boilers ranged from 4.0 to 11.2 kg t⁻¹, with uncertainties of 14–45% for different unit types. The emission factors of uncontrolled PM_2.5, PM₁₀, and total PM emitted by PC boilers were estimated to be 0.4A (where A is the percentage ash content of coal), 1.5A and 6.9A kg t⁻¹, respectively, with 95% CIs of 0.3A–0.5A, 1.1A–1.9A and 5.8A–7.9A. The analogous PM values for emissions with electrostatic precipitator (ESP) controls were 0.032A (95% CI: 0.021A–0.046A), 0.065A (0.039A–0.092A) and 0.094A (0.0656A–0.132A) kg t⁻¹, and 0.0147A (0.0092–0.0225A), 0.0210A (0.0129A–0.0317A), and 0.0231A (0.0142A–0.0348A) for those with both ESP and wet flue-gas desulfurization (wet-FGD). SO₂ and NO_X emission factors for Chinese power plants were smaller than those of U.S. EPA AP-42 database, due mainly to lower heating values of coals in China. PM emission factors for units with ESP, however, were generally larger than AP-42 values, because of poorer removal efficiencies of Chinese dust collectors. For units with advanced emission control technologies, more field measurements are needed to reduce emission factor uncertainties.

Mixing in the planetary boundary layer (PBL) affects vertical distributions of air tracers in the lower troposphere. An accurate representation of PBL mixing is critical for chemical-transport models (CTMs) for applications sensitive to simulations of the vertical profiles of tracers. The full mixing assumption in the widely used global CTM GEOS-Chem has recently been supplemented with a non-local PBL scheme. This study analyzes the impact of the non-local scheme on model representation of PBL mixing, consequences for simulations of vertical profiles of air tracers and surface air pollution, and implications for model applications to the interpretation of data retrieved from satellite remote sensing. The non-local scheme significantly improves simulations of the vertical distributions for NO₂ and O₃, as evaluated using aircraft measurements in summer 2004. It also reduces model biases over the U.S. by more than 10 ppb for surface ozone concentrations at night and by 2–5 ppb for peak ozone in the afternoon, as evaluated using ground observations. The application to inverse modeling of anthropogenic NO_x emissions for East China using satellite retrievals of NO₂ from OMI and GOME-2 suggests that the full mixing assumption results in 3–14% differences in top–down emission budgets as compared to the non-local scheme. The top–down estimate combining the non-local scheme and the Lin et al. inverse modeling approach suggests a magnitude of 6.6 TgN yr⁻¹ for emissions of NO_x over East China in July 2008 and 8.0 TgN yr⁻¹ for January 2009, with the magnitude and seasonality in good agreement with bottom–up estimates.

The Chinese government has moved aggressively since 2005 to reduce emissions of a number of pollutants including primary particulate matter (PM) and sulfur dioxide (SO₂), efforts inadvertently aided since late 2008 by economic recession. Satellite observations of aerosol optical depth (AOD) and column nitrogen dioxide (NO₂) provide independent indicators of emission trends, clearly reflecting the sharp onset of the recession in the fall of 2008 and rebound of the economy in the latter half of 2009. Comparison of AOD with ground-based observations of PM over a longer period indicate that emission-control policies have not been successful in reducing concentrations of aerosol pollutants at smaller size range over industrialized regions of China. The lack of success is attributed to the increasing importance of anthropogenic secondary aerosols formed from precursor species including nitrogen oxides (NO_x), non-methane volatile organic compounds (NMVOC), and ammonia (NH₃).

China's rapid economic growth has been accompanied by a high level of environmental degradation. One of the major sources of health and ecosystem damages is sulfur dioxide (SO₂). Reducing SO₂ emissions is a priority of China's environmental authorities, and the 11th Five-Year Plan (2006–2010) includes the target of reducing total SO₂ emissions by 10 percent from the 2005 level. Given the rapid increase in SO₂ emissions that is expected to occur in absence of intervention, attaining this target will require a significant effort. This article examines the two major policy measures the government is taking to achieve the SO₂ target: a shutdown of many small, inefficient power plants and the installation of desulfurization equipment on existing and new coal-fired plants. We present results from a joint U.S.–China study that we participated in, which estimated the costs and benefits of these policies. We then estimate the economy-wide impacts of the two policies using a multisector model of the Chinese economy. We find that in the aggregate, the economic benefits of the shutdown of the small power plants are large enough to offset the costs of the desulfurization equipment, even without considering the substantial environmental benefits from the reduction of emissions of SO₂ and other pollutants.

The concept of Global Warming Potentials
(GWPs) has been extensively used in policy consideration
as a relative index for comparing the climate impact of an
emitted greenhouse gas (GHG), relative to carbon dioxide
with equal mass emissions. Ozone depletion due to emission
of chlorinated or brominated halocarbons leads to cooling
of the climate system in the opposite direction to the direct
warming contribution by halocarbons as GHGs. This
cooling is a key indirect effect of the halocarbons on climatic
radiative forcing, which is accounted for by indirect GWPs.
With respect to climate, it is critical to understand net influences
considering direct warming and indirect cooling effects
especially for Halons due to the greater ozone-depleting efficiency
of bromine over chlorine. Until now, the indirect
GWPs have been calculated using a parameterized approach
based on the concept of Equivalent Effective Stratospheric
Chlorine (EESC) and the observed ozone depletion over the
last few decades. As a step towards obtaining indirect GWPs
through a more robust approach, we use atmospheric models
to explicitly calculate the indirect GWPs of Halon-1211
and Halon-1301 for a 100-year time horizon. State-of-theart
global chemistry-transport models (CTMs) were used as
the computational tools to derive more realistic ozone depletion
changes caused by an added pulse emission of the
two major Halons at the surface. The radiative forcings on
climate from the ozone changes have been calculated for indirect
GWPs using an atmospheric radiative transfer model
(RTM). The simulated temporal variations of global average
total column Halons after a pulse perturbation follow an exponential
decay with an e-folding time which is consistent
with the expected chemical lifetimes of the Halons. Our cal-
culated indirect GWPs for the two Halons are much smaller
than those from past studies but are within a single standard
deviation of WMO (2007) values and the direct GWP values
derived agree with the published values. Our model-based
assessment of the Halon indirect GWPs thus confirms the
significant importance of indirect effects on climate.

A series of aggressive measures was launched by
the Chinese government to reduce pollutant emissions from
Beijing and surrounding areas during the Olympic Games.
Observations at Miyun, a rural site 100 km downwind of the
Beijing urban center, show significant decreases in concentrations
of O3, CO, NOy, and SO2 during August 2008, relative
to August 2006–2007. The mean daytime mixing ratio
of O3 was lower by about 15 ppbv, reduced to 50 ppbv, in
August 2008. The relative reductions in daytime SO2, CO,
and NOy were 61%, 25%, and 21%, respectively. Changes in
SO2 and in species correlations from 2007 to 2008 indicate
that emissions of SO2, CO, and NOx were reduced at least
by 60%, 32%, and 36%, respectively, during the Olympics.
Analysis of meteorological conditions and interpretation of
observations using a chemical transport model suggest that
although the day-to-day variability in ozone is driven mostly
by meteorology, the reduction in emissions of ozone precursors
associated with the Olympic Games had a significant
contribution to the observed decrease in O3 during August
2008, accounting for 80% of the O3 reduction for the
month as a whole and 45% during the Olympics Period (8–
24 August). The model predicts that emission restrictions
such as those implemented during the Olympics can affect
O3 far beyond the Beijing urban area, resulting in reductions
in boundary layer O3 of 2–10 ppbv over a large region of the
North China Plain and Northeastern China.

An updated version of the nested-grid GEOSChem
model is developed allowing for higher horizontal
(0.5×0.667) resolution as compared to global models. CO
transport over a heavily polluted region, the Beijing-Tianjin-
Hebei (BTH) city cluster in China, and the pattern of outflow
from East China in summertime are investigated. Comparison
of the nested-grid with global models indicates that the
fine-resolution nested-grid model is capable of resolving individual
cities with high associated emission intensities. The
nested-grid model indicates the presence of a high CO column
density over the Sichuan Basin in summer, attributable
to the low-level stationary vortex associated with the Basin’s
topographical features. The nested-grid model provides good
agreement also with measurements from a suburban monitoring
site in Beijing during summer 2005. Tagged CO simulation
results suggest that regional emissions make significant
contributions to elevated CO levels over Beijing on polluted
days and that the southeastward moving cyclones bringing
northwest winds to Beijing are the key meteorological mechanisms
responsible for dispersion of pollution over Beijing in
summer. Overall CO fluxes to the NW Pacific from Asia are
found to decrease by a factor of 3–4 from spring to summer.
Much of the seasonal change is driven by decreasing
fluxes from India and Southeast Asia in summer, while
fluxes from East China are only 30% lower in summer than in
spring. Compared to spring, summertime outflow from Chinese
source regions is strongest at higher latitudes (north of
35 N). The deeper convection in summer transporting CO
to higher altitudes where export is more efficient is largely
responsible for enhanced export in summer.

Facing challenges of increased energy consumption and related regional air pollution, China has been aggressively implementing flue gas desulfurization (FGD) and phasing out small inefficient units in the power sector in order to achieve the national goal of 10% reduction in sulfur dioxide (SO₂) emissions from 2005 to 2010. In this paper, the effect of these measures on soil acidification is explored. An integrated methodology is used, combining emission inventory data, emission forecasts, air quality modeling, and ecological sensitivities indicated by critical load. National emissions of SO₂, oxides of nitrogen (NO_X), particulate matter (PM), and ammonia (NH₃) in 2005 were estimated to be 30.7, 19.6, 31.3, and 16.6 Mt, respectively. Implementation of existing policy will lead to reductions in SO₂ and PM emissions, while those of NO_X and NH₃ will continue to rise, even under tentatively proposed control measures. In 2005, the critical load for soil acidification caused by sulfur (S) deposition was exceeded in 28% of the country’s territory, mainly in eastern and south-central China. The area in exceedance will decrease to 26% and 20% in 2010 and 2020, respectively, given implementation of current plans for emission reductions. However, the exceedance of the critical load for nitrogen (N, combining effects of eutrophication and acidification) will double from 2005 to 2020 due to increased NO_X and NH₃ emissions. Combining the acidification effects of S and N, the benefits of SO₂ reductions during 2005−2010 will almost be negated by increased N emissions. Therefore abatement of N emissions (NO_X and NH₃) and deposition will be a major challenge to China, requiring policy development and technology investments. To mitigate acidification in the future, China needs a multipollutant control strategy that integrates measures to reduce S, N, and PM.

Simulation of summertime U.S. surface ozone diurnal cycle is influenced by the model representation of planetary boundary layer (PBL) mixing, spatial resolution, and precursor emissions. These factors are investigated here for five major regions (Northeast, Midwest, Southeast, California, and Southwest) by using the Model for Ozone And Related chemical Tracers version 2.4 (MOZART-2.4), with important modifications, to conduct sensitivity experiments for summer 1999 with three PBL mixing schemes, two horizontal resolutions and two emissions datasets. Among these factors, the PBL mixing is dominant. The default non-local scheme well reproduces the observed ozone diurnal variation, where the timing for the afternoon maximum and the morning minimum is within 1 h of the observed; biases for the minimum are less than 5 ppb except over the Southeast; and the ozone maximum–minimum contrast (OMMC) is within 10 ppb of observations except for the overprediction by 18.9 ppb over the Northeast. In contrast, the local scheme significantly overestimates the OMMC by 10–34 ppb over all regions as ozone and precursors are trapped too close to the ground. On the other hand, the full-mixing assumption underestimates the OMMC by 0–25 ppb, except over the Northeast, as the nighttime ozone decline is greatly underpredicted. As compared to PBL mixing, the effects of horizontal resolutions and precursor emissions being used are smaller but non-negligible. Overall, with the non-local mixing scheme, relatively high horizontal resolution (∼1.1°) and updated emissions data, the modified MOZART is capable of simulating the main features of the observed ozone diurnal cycle.

Large intra-season differences in mixing ratios of
CO and O3 were detected at Miyun, a rural site north of Beijing,
in summer 2006. Despite an increase in mean daytime
mixing ratio of CO from 500 ppbv in June to 700 ppbv in
July, mean daytime O3 dropped from 67 ppbv in June to 50
ppbv in July and August. The observed changes in CO and
O3 are attributed to the influence of the summer monsoonal
circulation that develops over the North China Plain in July.
Photochemical production of O3 is reduced as a consequence
of increased cloudiness during July and August, as indicated
by the strong negative correlation observed between O3 and
satellite observations of cloud optical depth, with cloudiness
having little effect on CO. The analysis suggests a strategy
for emission controls that could be implemented in an economically
efficient manner to minimize the frequency of high
levels of O3 during summer in Beijing.

An interdisciplinary, quantitative assessment of the health and economic costs of air pollution in China, and of market-based policies to build environmental protection into economic development.

An interdisciplinary, quantitative assessment of the health and economic costs of air pollution in China, and of market-based policies to build environmental protection into economic development.