Emission Control Measures Research Articles

Regional warming by black carbon and tropospheric ozone: A review of progresses and research challenges in China

Black carbon (BC) aerosol and tropospheric ozone (O4) are major air pollutants with short lifetimes of days to weeks in the atmosphere. These short-lived species have also made significant contributions to global warming since the preindustrial times (IPCC, 2013). Reductions in short-lived BC and tropospheric O3 have been proposed as a complementary strategy to reductions in greenhouse gases. With the rapid economic development, concentrations of BC and tropospheric O3 are relatively high in China, and therefore quantifying their roles in regional climate change is especially important. This review summarizes the existing knowledge with regard to impacts of BC and tropospheric O3 on climate change in China and defines critical gaps needed to assess the climate benefits of emission control measures. Measured concentrations of BC and tropospheric O3, optical properties of BC, as well as the model estimates of radiative forcing by BC and tropospheric O3 are summarized. We also review regional and global modeling studies that have investigated climate change driven by BC and tropospheric O3 in China; predicted sign and magnitude of the responses in temperature and precipitation to BC/O3 forcing are presented. Based on the review of previous studies, research challenges pertaining to reductions in short-lived species to mitigate global warming are highlighted.

Evaluation of health benefit using BenMAP-CE with an integrated scheme of model and monitor data during Guangzhou Asian Games

Guangzhou is the capital and largest city (land area: 7287km2) of Guangdong province in South China. The air quality in Guangzhou typically worsens in November due to unfavorable meteorological conditions for pollutant dispersion. During the Guangzhou Asian Games in November 2010, the Guangzhou government carried out a number of emission control measures that significantly improved the air quality. In this paper, we estimated the acute health outcome changes related to the air quality improvement during the 2010 Guangzhou Asian Games using a next-generation, fully-integrated assessment system for air quality and health benefits. This advanced system generates air quality data by fusing model and monitoring data instead of using monitoring data alone, which provides more reliable results. The air quality estimates retain the spatial distribution of model results while calibrating the value with observations. The results show that the mean PM2.5 concentration in November 2010 decreased by 3.5μg/m3 compared to that in 2009 due to the emission control measures. From the analysis, we estimate that the air quality improvement avoided 106 premature deaths, 1869 cases of hospital admission, and 20,026 cases of outpatient visits. The overall cost benefit of the improved air quality is estimated to be 165 million CNY, with the avoided premature death contributing 90% of this figure. The research demonstrates that BenMAP-CE is capable of assessing the health and cost benefits of air pollution control for sound policy making.

The “APEC Blue” phenomenon: Regional emission control effects observed from space

Observations from space were used to evaluate the effect of emission control measures on the changes of air pollutants in Beijing and its surroundings during the 2014 Asia-Pacific Economic Cooperation (APEC) Summit held in Beijing. Compared to the past three years (2011–2013), NO2 tropospheric vertical column densities in 2014 were found to exhibit almost across-the-board significant reductions over the North China Plain, suggesting the effectiveness of the national policy on NOx emission reduction during China's 12th “Five-Year-Plan”. During the APEC period (Nov. 3–11), AOD and AAOD were found reduced the most in Beijing, followed by Hebei province. Stringent emission control measures implemented in Beijing and the regional joint control over the surroundings especially in Hebei were responsible for the good air quality and so-called “APEC Blue”. However, air quality plummeted during the post-APEC period (Nov. 12–30), which was largely related to the lifting of local and regional joint emission control measures. By applying a spatial correlation analysis method, the potential emission source regions impacting air quality of Beijing included widespread areas in Hebei, Shandong, Shanxi, and Tianjin in the past three years (2011–2013). While during the study period in 2014, areas impacting Beijing evidently shrank and were limited within Hebei, suggesting evident effects of intense emission perturbations on lowering the extent of regional transport. This study indicates short-term measures did fix the air pollution problems in China but a permanent solution is still a tremendous challenge.

Evaluating the effects of China's pollution controls on inter-annual trends and uncertainties of atmospheric mercury emissions

Abstract. China's anthropogenic emissions of atmospheric mercury (Hg) are effectively constrained by national air pollution control and energy efficiency policies. In this study, improved methods, based on available data from domestic field measurements, are developed to quantify the benefits of Hg abatement by various emission control measures. Those measures include increased use of (1) flue gas desulfurization (FGD) and selective catalyst reduction (SCR) systems in power generation; (2) precalciner kilns with fabric filters (FF) in cement production; (3) mechanized coking ovens with electrostatic precipitators (ESP) in iron and steel production; and (4) advanced production technologies in nonferrous metal smelting. Investigation reveals declining trends in emission factors for each of these sources, which together drive a much slower growth of total Hg emissions than the growth of China's energy consumption and economy, from 679 metric tons (t) in 2005 to 750 t in 2012. In particular, estimated emissions from the above-mentioned four source types declined 3% from 2005 to 2012, which can be attributed to expanded deployment of technologies with higher energy efficiencies and air pollutant removal rates. Emissions from other anthropogenic sources are estimated to increase by 22% during the period. The species shares of total Hg emissions have been stable in recent years, with mass fractions of around 55, 39, and 6% for gaseous elemental Hg (Hg0), reactive gaseous mercury (Hg2+), and particle-bound mercury (Hgp), respectively. The higher estimate of total Hg emissions than previous inventories is supported by limited simulation of atmospheric chemistry and transport. With improved implementation of emission controls and energy saving, a 23% reduction in annual Hg emissions from 2012 to 2030, to below 600 t, is expected at the most. While growth in Hg emissions has been gradually constrained, uncertainties quantified by Monte Carlo simulation for recent years have increased, particularly for the power sector and particular industrial sources. The uncertainty (expressed as 95% confidence intervals) of Hg emissions from coal-fired power plants, for example, increased from −48–+73% in 2005 to −50–+89% in 2012. This is attributed mainly to increased penetration of advanced manufacturing and pollutant control technologies; the unclear operational status and relatively small sample sizes of field measurements of those processes have resulted in lower but highly varied emission factors. To reduce uncertainty and further confirm the benefits of pollution control and energy polices, therefore, systematic investigation of specific Hg pollution sources is recommended. The variability of temporal trends and spatial distributions of Hg emissions needs to be better tracked during the ongoing dramatic changes in China's economy, energy use, and air pollution status.

Biomonitoring of heavy metals in feathers of eleven common bird species in urban and rural environments of Tiruchirappalli, India.

Heavy metals continue to remain as a major environmental concern in spite of emission control measures. In this study, we analyzed the concentrations of heavy metals (Fe, Cr, Mn, Ni, Cu, Zn, and Cd) in the feathers of 11 species of birds collected from urban and rural areas of Tiruchirappalli, Southern India. Metal concentrations followed the order: Fe > Cu > Zn > Cr > Mn > Ni > Cd. Irrespective of sample locations, heavy metals such as Fe, Cr, Ni, Zn, and Cu were detected in high concentrations, while Cd and Mn were observed in lower concentrations. In contrary to our assumption, there were no statistically significant intraspecific and urban-rural differences in the metal concentrations except for Zn. Pairwise comparisons among species irrespective of metal type showed significant interspecific differences between Acridotheres tristis and Centropus phasianinus, A. tristis and Milvus migrans, C. phasianinus and M. migrans, M. migrans and Eudynamys scolopaceus, and Psittacula krameri and E. scolopaceus. Principal component analysis carried out for urban data extracted Ni, Mn, Zn, Fe, and Cu accounting for 48% variance implying dietary intake and external contamination as important sources for metals. In the rural, association of Zn, Cd, Ni, and Cr suggests the impact of metal fabrication industries and leather tanning operations.

Insight into characteristics and sources of PM2.5 in the Beijing–Tianjin–Hebei region, China

As the world’s second-largest economy, China has experienced severe air pollution with unprecedentedly high levels of PM2.5, i.e., particulate matter smaller than 2.5 m in diameter. The Ministry of Environmental Protection of China released an air pollution monitoring report for the year 2013 for the 74 largest cities of China. The Beijing-Tianjin-Hebei (BTH) region was classified as having the poorest air quality. The annual average PM2.5 concentration of the 13 cities in the BTH region was 106 g/m 3 . None of these cities met the new annual China Ambient Air Quality Standard (CAAQS), and 10.4–79.2% of the total days in 2013 met the daily CAAQS. Seven cities ranked in the top 10 with poorest air quality in the country. In January 2013, there were severe regional haze events in the BTH region, with the highest hourly PM2.5 concentration in Beijing exceeding 900 g/m 3 [1]. The deterioration of air quality is mainly because of the rapid economic growth and urbanization associated with heavy coal consumption, rapid increase in the number of vehicles, ongoing construction, and high population density. Economic development in the BTH region is uncoordinated and inefficient. Outdated industrial techniques and equipment are still used in many cities in Hebei Province. Inefficient fuel consumption and lagging emission control measures have led to high pollution emissions. In addition, the topography favors pollutant accumulation under weak southerly winds or stagnant weather conditions, since the region is surrounded on three sides by mountains. Major issues of PM2.5 pollution in the region and suggested future PM2.5 studies are illustrated in Figure 1.

Life-cycle assessment and control measures for carbon emissions of typical buildings in China

The construction industry plays an important role in economic and social development, yet it is also a primary source of carbon emissions. Accordingly, owing to global climate change, energy conservation and carbon reduction have become critical issues in the construction industry. However, to date, no established theory has been proposed for the life-cycle carbon assessment of typical buildings in China. To address this, the present study proposes a detailed carbon emission inventory for buildings and divides the life-cycle of a typical building into three stages based on material and energy flow: the materialization stage, the operation stage, and the disposal stage. Additionally, an analytical framework and evaluation indices are established and the proposed methodology is applied to three case studies. The results demonstrate that residential and office buildings with a reinforced concrete block masonry structure could reduce carbon emissions by 38–112 kgCO2/m2 compared with either a reinforced concrete structure or a brick–concrete structure. Although the operation stage appears to contribute approximately 82–86% of the total emissions, the materialization stage is also of considerable importance in alleviating the present environmental pressure. Furthermore, possible measures to control carbon during the materialization stage are proposed and evaluated, including optimization design of building structures based on carbon emissions and the selection of insulation materials. Accordingly, this study provides a standard method for life-cycle carbon assessment of buildings, which will be critical for future low-carbon development.

On the severe haze in Beijing during January 2013: Unraveling the effects of meteorological anomalies with WRF-Chem

Despite the stringent emission reduction measures implemented in Beijing over the past decade, a series of unprecedentedly severe haze events hit this megacity in January 2013. It is of great interest to find out the cause so as to provide a scientific basis for refining emission control measures. In the present study, we examine long-term (2000–2014) surface meteorological observations and simulate four recent winter haze episodes in 2010–2014 using a coupled meteorology-chemistry model (WRF-Chem). In addition to confirming the large-scale meteorological anomalies in northern China, the analysis of local meteorological parameters revealed that January 2013 had more frequent sustained weak southerly winds and high relative humidity in Beijing. Comparison of WRF-Chem simulations of the four episodes unambiguously shows that the combination of anomalously strong contribution of local and regional sources resulted into the extreme event in 2013: meteorological anomalies caused thicker temperature inversion, lower boundary layer, and hence stronger local accumulation of PM2.5 in urban Beijing (212 μg m−3 in 2013 case vs. 112–114 μg m−3 in historical cases); longer duration of southerly winds transported more pollutants to urban area (107 μg m−3 vs. 38–82 μg m−3) from eastern China. Our study also suggests that, although the emissions in Beijing have been decreased, they were still the major contributor (61–77%) to surface-layer PM2.5 over the urban area in recent winter episodes. Since adverse weather conditions such as those in January 2013 are uncontrollable, to alleviate severe haze pollution, Beijing must further strengthen its emission reduction measures and similar control should be extended to the entire eastern China.

The distribution and trends of fog and haze in the North China Plain over the past 30 years

Abstract. Frequent low visibility, haze and fog events were found in the North China Plain (NCP). Data throughout the NCP during the past 30 years were examined to determine the horizontal distribution and decadal trends of low visibility, haze and fog events. The impact of meteorological factors such as wind and relative humidity (RH) on those events was investigated. Results reveal distinct distributions of haze and fog days, due to their different formation mechanisms. Low visibility, haze and fog days all display increasing trends of before 1995, a steady stage during the period 1995–2003 and a drastically drop thereafter. All three events occurred most frequently during the heating season. Benefiting from emission control measures, haze and fog both show decreasing trends in winter during the past 3 decades, while summertime haze displays continuous increasing trends. The distribution of wind speed and wind direction as well as the topography within the NCP has determinative impacts on the distribution of haze and fog. Weakened south-easterly winds in the southern part of the NCP have resulted in high pollutant concentrations and frequent haze events along the foot of the Taihang Mountains. The orographically generated boundary layer wind convergence line in the central area of the southern NCP is responsible for the frequent fog events in this region. Wind speed has been decreasing throughout the entire southern NCP, resulting in more stable atmospheric conditions and weaker dispersion abilities, calling for harder efforts to control emissions to prevent haze events. Haze events are strongly influenced by the ambient RH. RH values associated with haze days are evidently increasing, suggesting that an increasing fraction of haze events are caused by the hygroscopic growth of aerosols, rather than simply by high aerosol loadings.

Including the temporal change in PM2.5 concentration in the assessment of human health impact: Illustration with renewable energy scenarios to 2050

This article proposes a new method to assess the health impact of populations exposed to fine particles (PM2.5) during their whole lifetime, which is suitable for comparative analysis of energy scenarios. The method takes into account the variation of particle concentrations over time as well as the evolution of population cohorts. Its capabilities are demonstrated for two pathways of European energy system development up to 2050: the Baseline (BL) and the Low Carbon, Maximum Renewable Power (LC-MRP). These pathways were combined with three sets of assumptions about emission control measures: Current Legislation (CLE), Fixed Emission Factors (FEFs), and the Maximum Technically Feasible Reductions (MTFRs). Analysis was carried out for 45 European countries. Average PM2.5 concentration over Europe in the LC-MRP/CLE scenario is reduced by 58% compared with the BL/FEF case. Health impacts (expressed in days of loss of life expectancy) decrease by 21%. For the LC-MRP/MTFR scenario the average PM2.5 concentration is reduced by 85% and the health impact by 34%. The methodology was developed within the framework of the EU's FP7 EnerGEO project and was implemented in the Platform of Integrated Assessment (PIA). The Platform enables performing health impact assessments for various energy scenarios.

Air quality in open-lot dairies and cattle feedyards

The research community is making good progress in understanding the mechanical, biochemical, and atmospheric processes responsible for airborne emissions of particulate matter (PM, or “dust”), gases, and vapors from open-lot livestock production, especially dairies and cattle feedyards. Recent studies in Texas, Kansas, Nebraska, Colorado, California, and Australia have expanded the available data on both emission rates and abatement measures. A national guidance document published by USDA last summer established what researchers believe to be the state of the art in estimating greenhouse-gas emissions from individual facilities. Although the uncertainties associated with our estimates of fugitive emissions are still unacceptably high, we have learned from our recent experience with ammonia that using a wide variety of credible measurement techniques, rather than focusing on 1 so-called “standard” technique, may be the better way to improve confidence in our estimates. The most promising control measures for gaseous emissions continue to be dietary strategies to increase nutrient-use efficiency, with management of corral-surface moisture a close second. For particulate matter, corral-surface management and moisture management may play comparable roles, depending on the mechanical strength of soils and the availability of water, respectively. The cost per unit reduction of emitted mass attributable to these abatement measures varies as widely as the emissions estimates themselves. Therefore, continued emphasis on process-based emissions research to reduce variances in emissions estimates, and to mitigate the contingency of prior, empirically based estimates is necessary. As a general rule, although cattle feedyard emission factors may be considered a reasonable starting point for estimating emissions from open-lot dairies, such estimates should be viewed with suspicion.

Research on Guilin Haze and Response Countermeasures

By statistics the 50a haze observation data in Guilin, and analyses on it’s changes from 1964 to 2013, we have studied the haze source and the countermeasures of Guilin. The haze days of Guilin has increased significantly in recent years, it closely related to the large-scale urban construction and rapid increase of cars. Haze is mainly affected by topography and local haze source in Guilin. By making pollutant emission control measures, the harm of haze can effectively reduced.

배출허용기준 대응기술을 고려한 국내 소형 경유 운행차의 대기오염물질 관리 방안

배출허용기준 대응기술을 고려한 국내 소형 경유 운행차의 대기오염물질 관리 방안

Factorization of air pollutant emissions: Projections versus observed trends in Europe

This paper revisits the emission scenarios of the European Commission's 2005 Thematic Strategy on Air Pollution (TSAP) in light of today's knowledge. We review assumptions made in the past on the main drivers of emission changes, i.e., demographic trends, economic growth, changes in the energy intensity of GDP, fuel-switching, and application of dedicated emission control measures. Our analysis shows that for most of these drivers, actual trends have not matched initial expectations. Observed ammonia and sulfur emissions in European Union in 2010 were 10% to 20% lower than projected, while emissions of nitrogen oxides and particulate matter exceeded estimates by 8% to 15%. In general, a higher efficiency of dedicated emission controls compensated for a lower-than-expected decline in total energy consumption as well as a delay in the phase-out of coal. For 2020, updated projections anticipate lower sulfur and nitrogen oxide emissions than those under the 2005 baseline, whereby the degree to which these emissions are lower depends on what assumptions are made for emission controls and new vehicle standards. Projected levels of particulates are about 10% higher, while smaller differences emerge for other pollutants. New emission projections suggest that environmental targets established by the TSAP for the protection of human health, eutrophication and forest acidification will not be met without additional measures.

A comparative assessment of economic-incentive and command-and-control instruments for air pollution and CO2 control in China's iron and steel sector

China's iron and steel sector is faced with increasing pressure to control both local air pollutants and CO2 simultaneously. Additional policy instruments are needed to co-control these emissions in this sector. This study quantitatively evaluates and compares two categories of emission reduction instruments, namely the economic-incentive (EI) instrument of a carbon tax, and the command-and-control (CAC) instrument of mandatory application of end-of-pipe emission control measures for CO2, SO2 and NOx. The comparative evaluation tool is an integrated assessment model, which combines a top-down computable general equilibrium sub-model and a bottom-up technology-based sub-model through a soft-linkage. The simulation results indicate that the carbon tax can co-control multiple pollutants, but the emission reduction rates are limited under the tax rates examined in this study. In comparison, the CAC instruments are found to have excellent effects on controlling different pollutants separately, but not jointly. Such results indicate that no single EI or CAC instrument is overwhelmingly superior. The environmental and economic effectiveness of an instrument highly depends on its specific attributes, and cannot be predicted by the general policy category. These findings highlight the necessity of clearer identification of policy target priorities, and detail-oriented and integrated policy-making among different governmental departments.

Concentrations, seasonal and diurnal variations of black carbon in PM2.5 in Shanghai, China

Concentration of black carbon (BC) in PM2.5 was measured continuously with an aethalometer during January 2010 and December 2011 at an urban site in Shanghai, China. The impact of the emission control measures for the 2010 World Expo and the World Expo event itself on the concentration and temporal variation of BC in Shanghai was discussed. The annually averaged BC concentrations in 2010 and 2011 in Shanghai were 3.8±2.3μgm−3 and 3.3±2.1μgm−3 respectively. Higher BC concentrations were found in winter and the lowest monthly concentration occurred in September. Comparing with the BC concentration in 2011, lower BC concentration was found in spring of 2010 due to the emission control measures for the Shanghai World Expo and higher BC concentration in summer due to the huge increase of visitors to the World Expo. Distinct bi-modal diurnal variation of BC was found with the highest evening peak concentration in Friday and the lowest in Monday. The diurnal variation of BC matched well with the living style of people in Shanghai and indicated that traffic emission was the main source of BC in urban Shanghai.

A 2600-year record of past polycyclic aromatic hydrocarbons (PAHs) deposition at Holzmaar (Eifel, Germany)

Polycyclic aromatic hydrocarbons (PAHs) are a proxy for climate- and human-related historical fire activity which has rarely been used beyond 1800AD. We explored the concentration and composition patterns of PAHs together with other proxies (charcoal, C, N, S, δ13C, δ15N, and δ34S) in a sediment core of Holzmaar as indicators of variations in climate and anthropogenic activity over the past 2600years. The concentrations of pyrogenic PAHs remained low (<500ngg−1) from the pre-Roman Iron Age (600BC) until the first significant increases to ca. 1000–1800ngg−1 between 1700 and 1750AD related to regional iron production. The highest increases in pyrogenic PAH concentrations occurred with industrialization peaking in the 1960s. PAH concentrations in most recent sediments decreased to pre-industrial levels because of emission control measures and the switch from coal to oil and gas as major fuel sources. Fluxes of PAHs (mgkm−2yr−1) increased in the order Migration Period and Early Middle Ages<pre-Roman Iron Ages<Roman era<High Middle Ages and Renaissance<pre-industrial modern period<industrial modern period. The changes of PAHs fluxes in pre-industrial times parallel known changes in local, regional and continental anthropogenic activity and climatic variations or their interactions across these historical periods. Perylene, a mainly biologically produced compound, was the dominant PAH in pre-industrial times. The Migration Period and the Early Middle Ages witnessed the most profound and simultaneous changes to the sedimentary organic matter properties in the past 2600years including the lowest PAH fluxes because of reduced human activity and more negative δ13C and δ15N values probably in response to colder and wetter conditions.

Impact of emission control on regional air quality: An observational study of air pollutants before, during and after the Beijing Olympic Games

An observational study on trace gases and PM2.5 was conducted at three sites in and around Beijing, during the Olympic season from 2007 to 2009. Air quality improved significantly during the Olympic Games due to the special emission control measures. However, concentrations of the primary pollutants and PM were found to have risen significantly after the Games. Although the major O3 precursors (NOx and VOCs) were well controlled during the Olympic season, O3 was still found to be the highest in 2008, based on the data of ground-based observation. All this information suggests that while control of regional emissions for the Beijing Olympic Games did improved the air quality in Beijing, more efforts will be needed for the continuous improvement of regional air quality, especially for significant reductions of O3 and fine particulate pollution, and not only in Beijing, but also in the Beijing-Tianjin-Hebei region.

PM2.5-bound oxygenated PAHs, nitro-PAHs and parent-PAHs from the atmosphere of a Chinese megacity: Seasonal variation, sources and cancer risk assessment

Polycyclic aromatic compounds (PACs) in air particulate matter contribute considerably to the health risk of air pollution. The objectives of this study were to assess the occurrence and variation in concentrations and sources of PM2.5-bound PACs [Oxygenated PAHs (OPAHs), nitro-PAHs and parent-PAHs] sampled from the atmosphere of a typical Chinese megacity (Xi'an), to study the influence of meteorological conditions on PACs and to estimate the lifetime excess cancer risk to the residents of Xi'an (from inhalation of PM2.5-bound PACs). To achieve these objectives, we sampled 24-h PM2.5 aerosols (once in every 6days, from 5 July 2008 to 8 August 2009) from the atmosphere of Xi'an and measured the concentrations of PACs in them. The PM2.5-bound concentrations of Σcarbonyl-OPAHs, ∑hydroxyl+carboxyl-OPAHs, Σnitro-PAHs and Σalkyl+parent-PAHs ranged between 5–22, 0.2–13, 0.3–7, and 7–387ngm−3, respectively, being markedly higher than in most western cities. This represented a range of 0.01–0.4% and 0.002–0.06% of the mass of organic C in PM2.5 and the total mass of PM2.5, respectively. The sums of the concentrations of each compound group had winter-to-summer ratios ranging from 3 to 8 and most individual OPAHs and nitro-PAHs had higher concentrations in winter than in summer, suggesting a dominant influence of emissions from household heating and winter meteorological conditions. Ambient temperature, air pressure, and wind speed explained a large part of the temporal variation in PACs concentrations. The lifetime excess cancer risk from inhalation (attributable to selected PAHs and nitro-PAHs) was six fold higher in winter (averaging 1450 persons per million residents of Xi'an) than in summer. Our results call for the development of emission control measures.

PM2.5 mass, chemical composition, and light extinction before and during the 2008 Beijing Olympics

AbstractDistinct contrast of air quality and visibility before and during the 2008 Beijing Olympic Games provides a rare opportunity to investigate the links between PM2.5 mass, chemical composition, and light extinction in this megacity. Twenty‐four hour integrated PM2.5 samples were collected, and light scattering coefficients and the concentrations of black carbon were measured at urban Beijing for this purpose during a measurement campaign from 1 July to 20 September 2008, which was classed into four stages according to the levels of emission control measures. Daily PM2.5 concentrations ranged from 15.9 to 156.7 µg m−3 with an average of 66.0 ± 35.1 µg m−3. The average PM2.5 mass during the Olympics decreased by 49% from the second stage (20 July to 7 August), mainly due to the reduction of secondary inorganic aerosols (i.e., sulfate, nitrate, and ammonium (SNA)). The counterintuitive increase of PM2.5 mass (by 27% on average) during the second stage with two most serious haze episodes, although more rigorous emission control measures were in place, compared to the first stage (1–19 July), was mainly explained by the unfavorable meteorology and input of sulfate aerosols. A daily PM2.5 mass threshold of 50 µg m−3 was extracted for frequent haze occurrence. The extinction fractions of SNA and organic material were each approximately 30% during the 20% best visibility days but changed to 81.7% and 8.4%, respectively, during the 20% worst visibility days. The results indicated that the role of SNA was magnified in haze formation during the 2008 summer in Beijing.