# Air Pollution, Greenhouse Gases & Climate

Dan Chen, Yuxuan Wang, Michael B. McElroy, Kebin He, Robert M Yantosca, and Phillipe Le Sager. 2009. “Regional CO pollution in China simulated by the high-resolution nested-grid GEOS-Chem model.” Atmospheric Chemistry and Physics, 9, 11, Pp. 3825-3839. Publisher's VersionAbstract
An updated version of the nested-grid GEOS-Chem 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. Compari-son of the nested-grid with global models indicates that the ﬁne-resolution nested-grid model is capable of resolving in-dividual cities with high associated emission intensities. The nested-grid model indicates the presence of a high CO col-umn 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 monitor-ing site in Beijing during summer 2005. Tagged CO simula-tion 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 mech-anisms 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 sum-mer. Much of the seasonal change is driven by decreas-ing 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 Chi-nese 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.
Xinyu Chen, Xi Lu, Michael B. McElroy, Chris P Nielsen, and Chongqing Kang. 2014. “Synergies of wind power and electrified space heating: A case study for Beijing.” Environmental Science & Technology, 48, 3, Pp. 2016–2024. Publisher's VersionAbstract

Demands for electricity and energy to supply heat are expected to expand by 71% and 47%, respectively, for Beijing in 2020 relative to 2009. If the additional electricity and heat are supplied solely by coal as is the current situation, annual emissions of CO2 may be expected to increase by 59.6% or 99 million tons over this interval. Assessed against this business as usual (BAU) background, the present study indicates that significant reductions in emissions could be realized using wind-generated electricity to provide a source of heat, employed either with heat pumps or with electric thermal storage (ETS) devices. Relative to BAU, reductions in CO2 with heat pumps assuming 20% wind penetration could be as large as 48.5% and could be obtained at a cost for abatement of as little as $15.6 per ton of avoided CO2. Even greater reductions, 64.5%, could be realized at a wind penetration level of 40% but at a higher cost,$29.4 per ton. Costs for reduction of CO2 using ETS systems are significantly higher, reflecting the relatively low efficiency for conversion of coal to power to heat.

Junling Huang and Michael B. McElroy. 2014. “Contributions of the Hadley and Ferrel circulations to the energetics of the atmosphere over the past 32 years.” Journal of Climate, 27, 7, Pp. 2656–2666. Publisher's VersionAbstract

The Hadley system provides an example of a thermally direct circulation; the Ferrel system in contrast provides an example of a thermally indirect circulation. In this study, the authors develop an approach to investigate the key thermodynamic properties of the Hadley and Ferrel systems, quantifying them using assimilated meteorological data covering the period January 1979–December 2010. This analysis offers a fresh perspective on the conversion of energy in the atmosphere from diabatic heating to the production of atmospheric kinetic energy. The results indicate that the thermodynamic efficiency of the Hadley system, considered as a heat engine, has been relatively constant over the 32-yr period covered by the analysis, averaging 2.6%. Over the same interval, the power generated by the Hadley regime has risen at an average rate of about 0.54 TW yr−1; this reflects an increase in energy input to the system consistent with the observed trend in the tropical sea surface temperatures. The Ferrel system acts as a heat pump with a coefficient of performance of 12.1, consuming kinetic energy at an approximate rate of 275 TW and exceeding the power production rate of the Hadley system by 77 TW.

Hongfei Cui, Pan Mao, Yu Zhao, Chris P Nielsen, and Jie Zhang. 2015. “Patterns in atmospheric carbonaceous aerosols in China: Emission estimates and observed concentrations.” Atmospheric Chemistry and Physics, 15, Pp. 8657–8678. Publisher's VersionAbstract

China is experiencing severe carbonaceous aerosol pollution driven mainly by large emissions from intensive use of solid fuels. To gain a better understanding of the levels and trends of carbonaceous aerosol emissions and the resulting ambient concentrations at the national scale, we update an emission inventory of anthropogenic organic carbon (OC) and elemental carbon (EC), and employ existing observational studies to analyze characteristics of these aerosols including temporal, spatial, and size distributions, and the levels and contributions of secondary organic carbon (SOC) to total OC. We further use ground observations to test the levels and inter-annual trends of the calculated national and provincial emissions of carbonaceous aerosols, and propose possible improvements in emission estimation for the future. The national OC emissions are estimated to have increased 29% from 2000 (2127 Gg) to 2012 (2749 Gg) and EC by 37% (from 1356 to 1857 Gg). The residential, industrial, and transportation sectors contributed an estimated 76±2%, 19±2% and 5±1% of the total emissions of OC, respectively, and 52±3%, 32±2% and 16±2% of EC. Updated emission factors based on the most recent local field measurements, particularly for biofuel stoves, lead to considerably lower emissions of OC compared to previous inventories. Compiling observational data across the country, higher concentrations of OC and EC are found in northern and inland cities, while larger OC/EC and SOC/OC ratios are found in southern cities, due to the joint effects of primary emissions and meteorology. Higher SOC/OC ratios are estimated at rural and background sites compared to urban ones, attributed to more emissions of OC from biofuel use, more biogenic emissions of volatile organic compound (VOC) precursors to SOC, and/or transport of aged aerosols. For most sites, higher concentrations of OC, EC, and SOC are observed in colder seasons, while SOC/OC is reduced, particularly at regional sites, attributed partly to weaker atmospheric oxidation and SOC formation compared to summer. Enhanced SOC formation from oxidization and anthropogenic activities like biomass combustion is judged to have crucial effects on severe haze events characterized by high particle concentrations. Several observational studies indicate an increasing trend in ambient OC/EC (but not in OC or EC individually) from 2000 to 2010, confirming increased atmospheric oxidation of OC across the country. Combining the results of emission estimation and observations, the improvement over prior emission inventories is indicated by inter-annual comparisons and correlation analysis. It is also indicated, however, that the estimated growth in emissions might be faster than observed growth, and that some sources with high primary OC/EC like burning of biomass are still underestimated. Further studies to determine changing emission factors over time in the residential sector and to compare to other measurements such as satellite observations are thus suggested to improve understanding of the levels and trends of primary carbonaceous aerosol emissions in China.

Yu Zhao, Chris P Nielsen, and Michael B. McElroy. 2012. “China's CO2 emissions estimated from the bottom up: Recent trends, spatial distributions, and quantification of uncertainties.” Atmospheric Environment, 59, Pp. 214-223. Publisher's VersionAbstract
China's emissions of anthropogenic CO2 are estimated using a bottom-up emission inventory framework based on a detailed categorization of economic sectors and provincial economic and energy data. It includes a newly compiled database of CO2 emission factors employing the latest field study results from China. Total annual emissions are estimated to have risen from 7126 to 9370 Mt CO2 from 2005 to 2009. Recent policies to conserve energy and reduce emissions have been effective in limiting CO2 emissions from power and iron & steel plants, but have had little effect on those from cement production. The uncertainties of China's CO2 emissions are quantified for the first time using Monte-Carlo simulation, producing a 95% confidence interval (CI) of −9% to +11% for total emissions in 2005. The largest contributors to sector-level emission uncertainty are emission factors for most industrial sources and activity levels for power plants, transportation, and residential & commercial sources. Application of province-level energy consumption and China-specific emission factors in some sectors results in higher annual emission estimates for 2005-2008 as compared with other studies, although most of those are within the 95% CIs of this study.
Chris P Nielsen and Mun S Ho. 2007. “Summary for policy.” In Clearing the air: The health and economic damages of air pollution in China, edited by Mun S Ho and Chris P Nielsen. Cambridge, MA: MIT Press. Publisher's VersionAbstract

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.

China's historic economic expansion is driven by fossil fuels, which increase its emissions of both local air pollutants and greenhouse gases dramatically. Clearing the Air is an innovative, quantitative examination of the national damage caused by China's degraded air quality, conducted in a pathbreaking, interdisciplinary U.S.-China collaboration. Its damage estimates are allocated by sector, making it possible for the first time to judge whether, for instance, power generation, transportation, or an unexpected source such as cement production causes the greatest environmental harm. Such objective analyses can reset policy priorities.

Clearing the Air uses this information to show how appropriate "green" taxes might not only reduce emissions and health damages but even enhance China's economic growth. It also shows to what extent these same policies could limit greenhouse gases, suggesting that wealthier nations have a responsibility to help China build environmental protection into its growth.

Clearing the Air is written for diverse readers, providing a bridge from underlying research to policy implications, with easily accessible overviews of issues and summaries of the findings for nonspecialists and policymakers followed by more specialized, interlinked studies of primary interest to scholars. Taken together, these analyses offer a uniquely integrated assessment that supports the book's economic and policy recommendations.

Michael B. McElroy and Yuxuan Wang. 2005. “Human and animal wastes: Implications for atmospheric N2O and NOX.” Global Biogeochemical Cycles, 19, 2. Publisher's VersionAbstract
More than 220 Tg N are processed annually through the global agriculture/animal/human food chain. It is suggested that aerobic denitrification, reduction of nitrite formed in the first stage of nitrification, is an important source not only of global N2O but also of NOx. A simple top‐down method indicates a globally averaged yield of 2% for N2O emitted as a consequence of human disturbances to the global nitrogen cycle. This yield can account not only for the contemporary budget of atmospheric N2O but also for trends observed over the past 1000 years. The associated microbial source of NOx is estimated assuming a NOx/N2O ratio of 3, consistent with results from a variety of laboratory and field studies. This source is significant, particularly for large developing countries such as China and India for which its contribution is comparable to that from fossil fuel.
Yu Zhao, Wei Wei, and Yu Lei. 2013. “An Anthropogenic Emission Inventory of Primary Air Pollutants in China for 2005 and 2010.” In Clearer Skies Over China: Reconciling Air Quality, Climate, and Economic Goals, Pp. 225-261. Cambridge, MA: MIT Press. Publisher's VersionAbstract

A groundbreaking U.S.–Chinese inquiry into the effects of recent air pollution controls and prospective carbon taxes on China's economy and environment.

China's carbon dioxide emissions now outstrip those of other countries and its domestic air quality is severely degraded, especially in urban areas. Its sheer size and its growing, fossil-fuel-powered economy mean that China's economic and environmental policy choices will have an outsized effect on the global environmental future. Over the last decade, China has pursued policies that target both fossil fuel use and atmospheric emissions, but these efforts have been substantially overwhelmed by the country's increasing energy demands. With a billion citizens still living on less than \$4,000 per year, China's energy and environmental policies must be reconciled with the goals of maintaining economic growth and raising living standards.

This book, a U.S.–Chinese collaboration of experts from Harvard and Tsinghua University, offers a groundbreaking integrated analysis of China's economy, emissions, air quality, public health, and agriculture. It first offers essential scientific context and accessible summaries of the book's policy findings; it then provides the underlying scientific and economic research. These studies suggest that China's recent sulfur controls achieved enormous environmental health benefits at unexpectedly low costs. They also indicate that judicious implementation of carbon taxes could reduce not only China's carbon emissions but also its air pollution more comprehensively than current single-pollutant policies, all at little cost to economic growth.

Qing Yang, Yingquan Chen, Haiping Yang, and Hanping Chen. 2016. “Greenhouse gas emissions of a biomass-based pyrolysis plant in China.” Renewable and Sustainable Energy Reviews, 53, January, Pp. 1580-1590. Publisher's VersionAbstract

Biomass pyrolysis offers an alternative to industrial coal-fired boilers and utilizes low temperature and long residence time to produce syngas, bio-oil and biochar. Construction of biomass-based pyrolysis plants has recently been on the rise in rural China necessitating research into the greenhouse gas emission levels produced as a result. Greenhouse gas emission intensity of a typical biomass fixed-bed pyrolysis plant in China is calculated as 1.55E−02 kg CO2-eq/MJ. Carbon cycle of the whole process was investigated and found that if 41.02% of the biochar returns to the field, net greenhouse gas emission is zero indicating the whole carbon cycle may be renewable. A biomass pyrolysis scenario analysis was also conducted to assess exhaust production, transportation distance and the electricity-generation structure for background information applied in the formulation of national policy.

Jin-Tai Lin, Michael B. McElroy, and K. Folkert Boersma. 2010. “Constraint of anthropogenic NOx emissions in China from different sectors: A new methodology using separate satellite retrievals.” Atmospheric Chemistry and Physics, 10, 1, Pp. 63-78. Publisher's VersionAbstract
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.
Youn Daeok, Kenneth O Patten, Jin-Tai Lin, and Donald J. Wuebbles. 2009. “Explicit calculation of indirect global warming potentials for halons using atmospheric models.” Atmospheric Chemistry and Physics, 9, 22, Pp. 8719-8733. Publisher's VersionAbstract
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-
Correspondence to: D. J. Wuebbles
(wuebbles@atmos.uiuc.edu)
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.
Sue J. Lin, I.J. Lu, and Charles Lewis. 2006. “Identifying key factors and strategies for reducing industrial CO2 emissions from a non-Kyoto protocol member’s (Taiwan) perspective.” Energy Policy, 34, Pp. 1499-1507. Publisher's VersionAbstract
In this study we use Divisia index approach to identify key factors affecting CO2 emission changes of industrial sectors in Taiwan. The changes of CO2 emission are decomposed into emission coefficient, energy intensity, industrial structure and economic growth. Furthermore, comparisons with USA, Japan, Germany, the Netherlands and South Korea are made to have a better understanding of emission tendency in these countries and to help formulate our CO2 reduction strategies for responding to the international calls for CO2 cuts. The results show that economic growth and high energy intensity were two key factors for the rapid increase of industrial CO2 emission in Taiwan, while adjustment of industrial structure was the main component for the decrease. Although economic development is important, Taiwan must keep pace with the international trends for CO2 reduction. Among the most important strategies are continuous efforts to improve energy intensity, fuel mix toward lower carbon, setting targets for industrial CO2 cuts, and advancing green technology through technology transfer. Also, the clean development mechanism (CDM) is expected to play an important role in the future.
Yu Zhao, Jie Zhang, and Chris P Nielsen. 2014. “The effects of energy paths and emission controls and standards on future trends in China's emissions of primary air pollutants.” Atmospheric Chemistry and Physics, 14, Pp. 8849-8868. Publisher's VersionAbstract
 To examine the efficacy of China's actions to control atmospheric pollution, three levels of growth of energy consumption and three levels of implementation of emission controls are estimated, generating a total of nine combined activity-emission control scenarios that are then used to estimate trends of national emissions of primary air pollutants through 2030. The emission control strategies are expected to have more effects than the energy paths on the future emission trends for all the concerned pollutants. As recently promulgated national action plans of air pollution prevention and control (NAPAPPC) are implemented, China's anthropogenic pollutant emissions should decline. For example, the emissions of SO2, NOx, total suspended particles (TSP), PM10, and PM2.5 are estimated to decline 7, 20, 41, 34, and 31% from 2010 to 2030, respectively, in the "best guess" scenario that includes national commitment of energy saving policy and implementation of NAPAPPC. Should the issued/proposed emission standards be fully achieved, a less likely scenario, annual emissions would be further reduced, ranging from 17 (for primary PM2.5) to 29% (for NOx) declines in 2015, and the analogue numbers would be 12 and 24% in 2030. The uncertainties of emission projections result mainly from the uncertain operational conditions of swiftly proliferating air pollutant control devices and lack of detailed information about emission control plans by region. The predicted emission trends by sector and chemical species raise concerns about current pollution control strategies: the potential for emissions abatement in key sectors may be declining due to the near saturation of emission control devices use; risks of ecosystem acidification could rise because emissions of alkaline base cations may be declining faster than those of SO2; and radiative forcing could rise because emissions of positive-forcing carbonaceous aerosols may decline more slowly than those of SO2 emissions and thereby concentrations of negative-forcing sulfate particles. Expanded control of emissions of fine particles and carbonaceous aerosols from small industrial and residential sources is recommended, and a more comprehensive emission control strategy targeting a wider range of pollutants (volatile organic compounds, NH3 and CO, etc.) and taking account of more diverse environmental impacts is also urgently needed.
Yu Lei, Qiang Zhang, Chris P Nielsen, and Kebin He. 2011. “An inventory of primary air pollutants and CO2 emissions from cement production in China, 1990-2020.” Atmospheric Environment, 45, 1, Pp. 147-154. Publisher's VersionAbstract
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 (NOX), 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 PM2.5, 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. NOX 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.