Atmospheric Environment (v.76, #C)

Science–policy interplay: Air quality management in the Pearl River Delta region and Hong Kong by Liuju Zhong; Peter K.K. Louie; Junyu Zheng; Zibing Yuan; Dingli Yue; Josephine W.K. Ho; Alexis K.H. Lau (3-10).
The information provided by the scientific studies and control measures implemented in the Pearl River Delta (PRD) region of China reveals that tremendous progress has been made in the understanding of regional air pollution issues and the deployment of mitigation measures for alleviating these problems. Given the unparalleled rapid economic growth in the PRD over the past two decades, such progress was only made possible by strong, science-based support and the partnerships between government and research institutions in the region and overseas. Researchers from these partnership programs and related studies have deployed cutting-edge expertise and experience in various crucial mainland China and mainland China/Hong Kong-level projects. China recognizes the importance of protecting the environment and cleaning up the air in the pursuit of sustainable growth and economic development. To avoid falling into a cycle of event-driven clean-up efforts, China has recently taken a major step and updated the national ambient air quality standards. Clearly, China is implementing an increasing number of evidence-based policies to address air pollution problems. Thus, to bring a fresh impetus at a national level, the PRD must maintain and augment the Hong Kong-mainland collaborative momentum, inducing a “whole-China” effort to clean up air pollution. To strengthen the science-based support system and ensure continuous and concerted effort in implementing the regional multi-pollutant control strategy, there must be an overarching and integral Hong Kong–Guangdong science consortium framework supporting the formulation of regional policy and control measures built on common goals under the “one country, two systems” principle. The “PRD Approach” of the air quality management regime reflected regional cooperative efforts in synchronous air pollutant control, catalyzed the crucial role of information disclosure and subtly transformed the air quality management approach to overcome the nation's new air pollution challenges.
Keywords: PRD; Regional air quality management; Multi-pollutant control strategy; Science–policy interplay;

Emission trends and source characteristics of SO2, NO x , PM10 and VOCs in the Pearl River Delta region from 2000 to 2009 by Qing Lu; Junyu Zheng; Siqi Ye; Xingling Shen; Zibing Yuan; Shasha Yin (11-20).
Emission trends and variations in source contributions of SO2, NO x , PM10 and VOCs in the Pearl River Delta (PRD) region from 2000 to 2009 were characterized by using a dynamic methodology, taking into account the economic development, technology penetration, and emission control. The results indicated that SO2 emissions increased rapidly during 2000–2005 but decreased significantly afterward. NO x emissions went up consistently during 2000–2009 except for a break point in 2008. PM10 emissions increased by 76% during 2000–2007 but started to decrease slightly in the following years. VOCs emissions presented continuous increase during the study period. Power plants and industrial sources were consistently the largest SO2 and PM10 emission contributors. The on-road mobile source was the largest emission contributor for VOCs and NO x emissions with decreasing contributions. The NO x contribution from power plants and industrial sources kept increasing. Worthy of mention is that the non-road mobile source is becoming an important SO2 and NO x contributor in this region. Comparisons with satellite data, ground observations and national trends indicated that emission trends developed in this study were reasonable. Implications for future air pollution control policies were discussed.► PRD emission trends were characterized and validated from 2000–2009. ► Variations in source characteristics were investigated and analyzed. ► SO2 emission began to decrease from 2005, while PM10 emission decreased from 2007. ► NO x and VOCs emissions exhibited upward trends during 2000–2009. ► Immediate control is needed on marine emission source in the PRD region.
Keywords: Emission estimation; Source contribution; Control policy; Satellite data; Ground observations;

Despite extensive emission control measures targeting motor vehicles and to a lesser extent other sources, annual-average PM10 mass concentrations in Hong Kong have remained relatively constant for the past several years and for some air quality metrics, such as the frequency of poor visibility days, conditions have degraded. The underlying drivers for these long-term trends were examined by performing source apportionment on eleven years (1998–2008) of data for seven monitoring sites in the Hong Kong PM10 chemical speciation network. Nine factors were resolved using Positive Matrix Factorization. These factors were assigned to emission source categories that were classified as local (operationally defined as within the Hong Kong Special Administrative Region) or non-local based on temporal and spatial patterns in the source contribution estimates. This data-driven analysis provides strong evidence that local controls on motor vehicle emissions have been effective in reducing motor vehicle-related ambient PM10 burdens with annual-average contributions at neighborhood- and larger-scale monitoring stations decreasing by ∼6 μg m−3 over the eleven year period. However, this improvement has been offset by an increase in annual-average contributions from non-local contributions, especially secondary sulfate and nitrate, of ∼8 μg m−3 over the same time period. As a result, non-local source contributions to urban-scale PM10 have increased from 58% in 1998 to 70% in 2008. Most of the motor vehicle-related decrease and non-local source driven increase occurred over the period 1998–2004 with more modest changes thereafter. Non-local contributions increased most dramatically for secondary sulfate and secondary nitrate factors and thus combustion-related control strategies, including but not limited to power plants, are needed for sources located in the Pearl River Delta and more distant regions to improve air quality conditions in Hong Kong. PMF-resolved source contribution estimates were also used to examine differential contributions of emission source categories during high PM episodes compared to study-average behavior. While contributions from all source categories increased to some extent on high PM days, the increases were disproportionately high for the non-local sources. Thus, controls on emission sources located outside the Hong Kong Special Administrative Region will be needed to effectively decrease the frequency and severity of high PM episodes.► Positive Matrix Factorization is applied to identify PM10 sources in Hong Kong. ► Local and non-local PM10 sources are classified based on spatiotemporal variations. ► Local control measures on vehicle exhaust are effective with more than 50% reduction. ► Local reduction is totally offset by increased contributions from non-local sources. ► A coordinated, regional-scale air quality management plan is urgently needed.
Keywords: Particulate matter; Long-term trend; Control strategy; Positive Matrix Factorization; Hong Kong;

Historical evaluation of vehicle emission control in Guangzhou based on a multi-year emission inventory by Shaojun Zhang; Ye Wu; Huan Liu; Xiaomeng Wu; Yu Zhou; Zhiliang Yao; Lixin Fu; Kebin He; Jiming Hao (32-42).
The Guangzhou government adopted many vehicle emission control policies and strategies during the five-year preparation (2005–2009) to host the 2010 Asian Games. This study established a multi-year emission inventory for vehicles in Guangzhou during 2005–2009 and estimated the uncertainty in total vehicle emissions by taking the assumed uncertainties in fleet-average emission factors and annual mileage into account. In 2009, the estimated total vehicle emissions in Guangzhou were 313 000 (242 000–387 000) tons of CO, 60 900 (54 000–70 200) tons of THC, 65 600 (56 800–74 100) tons of NO x and 2740 (2100–3400) tons of PM10. Vehicle emissions within the urban area of Guangzhou were estimated to be responsible for ∼40% of total gaseous pollutants and ∼25% of total PM10 in the entire city. Although vehicle use intensity increased rapidly in Guangzhou during 2005–2009, vehicle emissions were estimated to have been reduced by 12% for CO, 21% for THC and 20% for PM10 relative to those in 2005. NO x emissions were estimated to have remained almost constant during this period. Compared to the “without control” scenario, 19% (15%–23%) of CO, 20% (18%–23%) of THC, 9% (8%–10%) of NO x and 16% (12%–20%) of PM10 were estimated to have been mitigated from a combination of the implementation of Euro III standards for light-duty vehicles (LDVs) and heavy-duty diesel vehicles and improvement of fuel quality. This study also evaluated several enhanced vehicle emission control actions taken recently. For example, the enhanced I/M program for LDVs was estimated to reduce 11% (9%–14%) of CO, 9% (8%–10%) of THC and 2% (2%–3%) of NO x relative to total vehicle emissions in 2009. Total emission reductions by temporary traffic controls for the Asian Games were estimated equivalent to 9% (7%–11%) of CO, 9% (8%–10%) of THC, 5% (5%–6%) of NO x and 10% (8%–13%) of PM10 estimated total vehicle emissions in 2009. Those controls are essential to further vehicle emission mitigation in Guangzhou required by the new National Ambient Air Quality Standards.► An emission inventory is established for Guangzhou vehicle fleet, 2005–2009. ► Vehicle emissions in the urban area in 2009 were estimated based on traffic data. ► A retrospective evaluation has been performed for major controls during 2005–2009. ► Several recent controls have been assessed against vehicle emissions in 2009. ► Deterioration of traffic conditions could offset the benefit of emission controls.
Keywords: Vehicle; Guangzhou; Emission control; Emission factor;

The release of large amounts of sulfur dioxide (SO2) and nitrogen oxides (NO x ) from the burning of fossil fuel leads to regional air pollution phenomena such as haze and acidic deposition. Despite longstanding recognition of the severity of these problems and the numerous studies conducted in China, little is known of long-term trends in particulate sulfate and nitrate and their association with changes in precursor emissions. In this study, we analyze records covering a 14-year period (1995–2008) of PM10 composition in the subtropical city of Hong Kong, situated in the rapidly developing Pearl River Delta region of southern China. A linear regression method and a Regional Kendall test are employed for trend calculations. In contrast to the decreased levels of SO2 and NO x emissions in Hong Kong, there are increasing overall trends in ambient concentrations of PM10 sulfate and PM10 nitrate, with the most obvious rise seen during 2001–2005. The percentages of sulfate and nitrate in the PM10 mass and rainwater acidity also increased. Backward trajectories are computed to help identify the origin of large-scale air masses arriving in Hong Kong. In air masses dominated by Hong Kong urban sources and ship emissions, there was no statistically significant trend for PM10 sulfate and a small increase for PM10 nitrate; however, the evident increases in PM10 sulfate and PM10 nitrate concentrations were observed in air masses originating from eastern China and are generally consistent with changes in emissions of their precursors in eastern China. Examination of PM10 mass data recorded at a pair of upwind-urban sites also indicates that long-range transport makes a large contribution (>80%) to PM10 loadings in Hong Kong. Together with our previous study on the ozone trend, these results demonstrate the important impact exerted by long-distance sources and suggest a need to consider the impact of super-regional transport when formulating air-quality management strategy in Hong Kong in future.► Ambient concentrations of PM10 sulfate and nitrate have increased during the period. ► The PM10 sulfate trends are generally consistent with changes of SO2 emissions in China. ► The results demonstrate emissions transported from distant sources can impact local air quality.
Keywords: Sulfate; Nitrate; PM10; Wet deposition acidity; Emissions; Air masses; Long-distance source;

Developing a risk-based air quality health index by Tze Wai Wong; Wilson Wai San Tam; Ignatius Tak Sun Yu; Alexis Kai Hon Lau; Sik Wing Pang; Andromeda H.S. Wong (52-58).
We developed a risk-based, multi-pollutant air quality health index (AQHI) reporting system in Hong Kong, based on the Canadian approach. We performed time series studies to obtain the relative risks of hospital admissions for respiratory and cardiovascular diseases associated with four air pollutants: sulphur dioxide, nitrogen dioxide, ozone, and particulate matter with an aerodynamic diameter less than 10 μm (PM10). We then calculated the sum of excess risks of the hospital admissions associated with these air pollutants. The cut-off points of the summed excess risk, for the issuance of different health warnings, were based on the concentrations of these pollutants recommended as short-term Air Quality Guidelines by the World Health Organization. The excess risks were adjusted downwards for young children and the elderly. Health risk was grouped into five categories and sub-divided into eleven bands, with equal increments in excess risk from band 1 up to band 10 (the 11th band is ‘band 10+’). We developed health warning messages for the general public, including at-risk groups: young children, the elderly, and people with pre-existing cardiac or respiratory diseases. The new system addressed two major shortcomings of the current standard-based system; namely, the time lag between a sudden rise in air pollutant concentrations and the issue of a health warning, and the reliance on one dominant pollutant to calculate the index. Hence, the AQHI represents an improvement over Hong Kong's existing air pollution index.► We developed an air quality health index based on excess risk of morbidities. ► Excess risks were derived from time series analyses of data on hospital admissions. ► Risk categories were constructed based on the WHO Air Quality Guidelines. ► Advisory messages were developed for the general public including high-risk groups. ► This index has a short lag time and reflects health risk from multiple pollutants.
Keywords: Air pollution index; Health risk; Respiratory disease; Cardiovascular disease; Hospital admissions; Hong Kong;

The short-term effect of ambient ozone on mortality is modified by temperature in Guangzhou, China by Tao Liu; Tian Tian Li; Yong Hui Zhang; Yan Jun Xu; Xiang Qian Lao; Shannon Rutherford; Cordia Chu; Yuan Luo; Qi Zhu; Xiao Jun Xu; Hui Yan Xie; Zhao Rong Liu; Wen Jun Ma (59-67).
Effects of ozone on mortality have been widely assessed in developed countries but rarely in developing countries, and the effects of season and temperature on these associations remain unclear. The present study aimed to explore the modifying effects of temperature on the association of ozone with mortality, and to examine the lag effect structure in Guangzhou, China. Daily non-accidental mortality, air pollution and meteorological data from January 1st 2006 to December 31st 2008 in Guangzhou were collected. Generalized additive models (GAM) and distributed lag models (DLM) were used to estimate the excess risk (ER) of ozone on daily mortality and capture the lag effect structure. Results revealed that, in cold season, an increment in the ozone concentration of 10 μg m 3 was associated with a 0.87% (95% CI: −0.06 to 2.29%) and 3.34% (95%CI: 1.36–5.35%) increase of mortality for lag0 and lag0–6, respectively. However, no significant effects were observed in the warm season. Daily average temperature and ozone concentration had interactive negative effects on non-accidental mortality in the cold season and at daily average temperatures in the 0–25th percentile, and mortality displacement was also found in these conditions. Therefore, the short-term effect of ambient ozone on mortality is modified by temperature in Guangzhou, China.► Ambient ozone had independent effects on non-accidental mortality in cold season. ► The effects of ozone lasted longer in cold season and low temperature days. ► Mortality displacement was observed in days with low temperature. ► The risk assessment might be underestimated by using single-day exposure model.
Keywords: Ambient ozone; Non-accidental mortality; Lag effect; Time-series study; Mortality displacement;

Gaseous air pollution and acute myocardial infarction mortality in Hong Kong: A time-stratified case-crossover study by Hualiang Lin; Qingzhu An; Chao Luo; Vivian C. Pun; Chi Sing Chan; Linwei Tian (68-73).
Acute myocardial infarction (AMI) is a common disease with serious consequences in mortality and morbidity. An association between gaseous air pollution and AMI has been suggested, but the epidemiological evidence is still limited. For the study period 1998–2010, daily counts of AMI deaths were collected, as well as daily air pollution data including concentrations of particulates (PM10), nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3) and carbon monoxide (CO) were also obtained. The associations between gaseous air pollutants and AMI mortality were estimated using time-stratified case-crossover analyses. NO2 and SO2 were found to be significantly associated with increased AMI mortality. The odds ratios (ORs) were 1.0455 (95% confidence interval (CI): 1.017–1.0748) and 1.0256 (95% CI: 1.0027–1.0489) for an interquartile range (IQR) increase in the current day's NO2 and SO2 concentration, respectively, and this association persisted in 2-pollutant models; and no association was observed for CO and O3. It is likely that exposure to elevated ambient NO2 and SO2 air pollution contributed to increased AMI mortality.► Elevated ambient NO2 contributed to increased AMI mortality in Hong Kong. ► Ambient SO2 was associated with increased AMI mortality in Hong Kong. ► No effects on AMI mortality were detected for O3 and CO.
Keywords: Gaseous air pollution; Acute myocardial infarction; Mortality; Case-crossover;

Season and humidity dependence of the effects of air pollution on COPD hospitalizations in Hong Kong by Hong Qiu; Ignatius Tak Sun Yu; Xiaorong Wang; Linwei Tian; Lap Ah Tse; Tze Wai Wong (74-80).
Associations between ambient pollution and respiratory morbidity including chronic obstructive pulmonary disease (COPD) have been confirmed. Weather factors, such as temperature, season and relative humidity (RH), may modify the effects of air pollution. This time series study was conducted to examine whether the effects of air pollution on emergency COPD hospital admissions in Hong Kong varied across seasons and RH levels, and explore the possible joint modification of season and RH on the effects of pollution. Data of daily air pollution concentrations mean temperature and RH, and COPD hospital admissions from 1998 to 2007 were collected. Generalized additive Poisson models with interaction terms were used to estimate the effects of pollution across seasons and RH levels. We observed an increase in the detrimental effects of air pollution in the cool season and on low humidity days. On the cool and dry days, a 10 μg m−3 increment of lag03 exposure was associated with an increase in emergency COPD admissions by 1.76% (95%CI: 1.19–2.34%), 3.43% (95%CI: 2.80–4.07%), and 1.99% (95%CI: 0.90–3.09%) for nitrogen dioxide (NO2), ozone (O3), and sulfur dioxide (SO2), respectively, all of which were statistically significantly higher than those on the other days. No consistent modification of weather factors was found for the effects of particles with an aerodynamic diameter less than 10 μm (PM10). The results suggested that season and RH jointly modified the effects of gaseous pollutants, resulting in increased emergency COPD hospitalizations on the cool and dry days.► Gaseous pollutants increased COPD hospitalizations more in cool season. ► Air pollutants increased COPD hospitalizations more on days with low humidity. ► The effects of gaseous pollutants were greatest on the cool and dry days. ► Season and humidity jointly modified the effects of gaseous pollutants.
Keywords: Chronic obstructive pulmonary disease; Emergency hospital admissions; Gaseous pollutants; Time series study; Weather factors;

Emission controls and changes in air quality in Guangzhou during the Asian Games by Huan Liu; Xuemei Wang; Jinpu Zhang; Kebin He; Ye Wu; Jiayu Xu (81-93).
With the new air quality standards forthcoming in China, the Pearl River Delta region is facing new challenges to achieve its air quality goal. The success of the emission reduction measures introduced by local authorities in the run-up to the Guangzhou Asian Games demonstrated that the Pearl River Delta air quality can be improved by introducing integrated emission reduction measures. This paper combines observation data, emission reduction measures, and air quality simulations that were applied during the Asian Games (12–27 November 2010) to analyze the relationship between emissions and concentrations of pollutants in Guangzhou. The Asian Games abatement strategy totally reduced emissions of 41.1% SO2, 41.9% NO x , 26.5% PM10, 25.8% PM2.5 and 39.7% VOC. The concentrations of SO2, NO2, PM10 and PM2.5 were reduced by 66.8%, 51.3%, 21.5% and 17.1%, respectively. In Guangzhou, the main challenge to be overcome with the new air quality daily requirements is mostly for NO2, PM2.5, and hourly ozone maxima. If pollutants maintain the same concentrations before and after the Asian Games, there will be 47.4% and 31.6% non-attainment days for NO2 and PM2.5 respectively as a period average. Although PM10 concentration can meet the daily limits (150 μg m−3), it is quite difficult to meet the annual limit value (70 μg m−3). One important implication is that the long-term, step-by-step integrated measures of the past six years work better than the strict, intensive, short-term measures on SO2, NO2 and VOC control. Dust control by limiting construction sites and watering the roads can further reduce 12.8% of the PM10 concentration. However, to reduce ambient PM2.5, the abatement strategy should be more complex and extensive. On the contrary, ozone pollution was not improved during the Asian Games, indicating that alleviation strategies should be improved by scientific studies to determine the appropriate control ratio of NO2 and VOC in the Pearl River Delta region.► This paper analyzes the emissions and pollutants concentrations in PRD region. ► The new daily concentration standards of NO2 and PM2.5 are difficult to meet. ► To reduce PM2.5, the abatement strategy should consider gases and PM pollutants. ► PM10 concentration can meet the daily limits, but hard to meet the new annual limit.
Keywords: Emission control; New ambient air quality standards; STEM model; Guangzhou Asian Games; Pearl River Delta;

Characteristics of fine particulate non-polar organic compounds in Guangzhou during the 16th Asian Games: Effectiveness of air pollution controls by H.M. Xu; J. Tao; Steven Sai Hang Ho; K.F. Ho; J.J. Cao; N. Li; Judith C. Chow; G.H. Wang; Y.M. Han; R.J. Zhang; John G. Watson; J.Q. Zhang (94-101).
The concentrations of organic compounds, including n-alkanes and polycyclic aromatic hydrocarbons (PAHs), in fine particles (PM2.5) were measured in an urban area of Guangzhou before, during, and after the 16th Asian Games (9–30 November 2010). Higher average concentrations of n-alkanes and PAHs occurred in the nighttime, presumably due to a restriction on motor vehicle operation during the day and the accumulation of pollutants due to temperature inversions at night. The carbon preference index, contributions of wax n-alkanes, and PAHs diagnostic ratios indicated that the main sources of n-alkanes and PAHs were anthropogenic, especially motor vehicle emissions. The CMAQ model was used to estimate the percentages of biogenic organic aerosol in the total organic aerosol, then the ratios of source marker PAHs to biogenic organic carbon were used to evaluate the air pollution control policies effectiveness during the Asian Games.► Vehicular emissions were the major contributors to atmosphere during the Games. ► n-Alkanes and PAHs were more abundant in the nighttime than those in the daytime. ► PAHs/biogenic OC were used to evaluate the effectiveness of air pollution controls.
Keywords: n-Alkane; PAH; Asian Games; Pollution control policy; PM2.5;

Policy change driven by an AIS-assisted marine emission inventory in Hong Kong and the Pearl River Delta by Simon K.W. Ng; Christine Loh; Chubin Lin; Veronica Booth; Jimmy W.M. Chan; Agnes C.K. Yip; Ying Li; Alexis K.H. Lau (102-112).
A new exhaust emission inventory of ocean-going vessels (OGVs) was compiled for Hong Kong by using Automatic Identification System (AIS) data for the first time to determine typical main engine load factors, through vessel speed and operation mode characterization. It was found that in 2007, container vessel was the top emitting vessel type, contributing 9,886, 11,480, 1,173, 521 and 1166 tonnes of SO2, NO x , PM10, VOC and CO, respectively, or about 80%–82% of the emissions. The top five, which also included ocean cruise, oil tanker, conventional cargo vessel and dry bulk carrier, accounted for about 98% of emissions. Emission maps, which add a new spatial dimension to the inventory, show the key emission hot spots in Hong Kong and suggest that a significant portion of emissions were emitted at berth. Scientific evidence about the scale and distribution of ship emissions has contributed in raising public awareness and facilitating stakeholder engagement about the issue. Fair Winds Charter, the world's first industry-led voluntary emissions reduction initiative, is a perfect example of how careful scientific research can be used in public engagement and policy deliberation to help drive voluntary industry actions and then government proposals to control and regulate marine emissions in Hong Kong and the Pearl River Delta region.► A detail activity-based marine vessels emission inventory for Hong Kong. ► Automatic Identification System (AIS) data used to determine main engine load factors. ► Container vessel was top emitter in 2007, contributed about 80% of marine emissions. ► Emission maps identify at-berth emission hot-spots for effective control policies. ► Fair Winds Charter: a case of industry action and policy change driven by science.
Keywords: Ship emissions; Automatic Identification System; Emission map; Government policy; Hong Kong; Pearl River Delta;

Reductions in sulfur pollution in the Pearl River Delta region, China: Assessing the effectiveness of emission controls by Xuemei Wang; Huan Liu; Jiongming Pang; Gregory Carmichael; Kebin He; Qi Fan; Liuju Zhong; Zhiyong Wu; Jinpu Zhang (113-124).
Total emission control of sulfur has been stringently implemented in the last two five-year plans (2000–2010), as a key national environmental policy in China. As a result of this policy, SO2 emissions in the Pearl River Delta (PRD) region were reduced by 212.5 kilotons. The regional monitoring network data indicate a 39% reduction of ambient SO2 concentrations between 2006 and 2009. SCIAMACHY satellite data show a 27% decrease in the whole column SO2 concentration during the same period. To assess what role changes in meteorology contributed to the observed changes in concentrations in this time period, sensitive experiments for November of 2006 and 2009 where different combinations of changing emissions under constant meteorology and vice versa were simulated using the MM5-STEM model. In general, the model can well capture the day-to-day variation patterns of meteorology and ambient SO2. At the regional scale, long-term emission controls constantly reduce ambient SO2 and sulfate concentrations, while meteorology has negative and positive effects in the PRD. The contribution of meteorological effects to the composite difference of SO2 concentration varied in different cities, ranging from −20% to 33%. According to meteorological effects, three categories of cities were established and indicated the meteorological role in different cities. Regional transport is very important to WQS site, ranging from −39 to +67 μg m−3 for the SO2 concentration. Both the meteorological conditions and trans-boundary transport play important and complex role in the linkage between emission and ambient concentration.
Keywords: Sulfur dioxide; Control policy; Meteorological effect; MM5/STEM;

VOCs and OVOCs distribution and control policy implications in Pearl River Delta region, China by Peter K.K. Louie; Josephine W.K. Ho; Roy C.W. Tsang; Donald R. Blake; Alexis K.H. Lau; Jian Zhen Yu; Zibing Yuan; Xinming Wang; Min Shao; Liuju Zhong (125-135).
Ambient air measurements of volatile organic compounds (VOCs) and oxygenated volatile organic compounds (OVOCs) were conducted and characterised during a two-year grid study in the Pearl River Delta (PRD) region of southern China. The present grid study pioneered the systematic investigation of the nature and characteristics of complex VOC and OVOC sources at a regional scale. The largest contributing VOCs, accounting over 80% of the total VOCs mixing ratio, were toluene, ethane, ethyne, propane, ethene, butane, benzene, pentane, ethylbenzene, and xylenes. Sub-regional VOC spatial characteristics were identified, namely: i) relatively fresh pollutants, consistent with elevated vehicular and industrial activities, around the PRD estuary; and ii) a concentration gradient with higher mixing ratios of VOCs in the west as compared with the eastern part of PRD. Based on alkyl nitrate aging determination, a high hydroxyl radical (OH) concentration favoured fast hydrocarbon reactions and formation of locally produced ozone. The photochemical reactivity analysis showed aromatic hydrocarbons and alkenes together consisted of around 80% of the ozone formation potential (OFP) among the key VOCs. We also found that the OFP from OVOCs should not be neglected since their OFP contribution was more than one-third of that from VOCs alone. These findings support the choice of current air pollution control policy which focuses on vehicular sources but warrants further controls. Industrial emissions and VOCs emitted by solvents should be the next targets for ground-level ozone abatement.► The first and foremost large spatial–temporal VOCs grid study in the PRD region. ► More detailed VOCs spatial emission characteristics were identified. ► High OH concentration in PRD favoured fast reactions and ozone formation. ► Ozone formation potential of VOCs and OVOCs were analysed. ► Findings supported further control measures and policies formulation.
Keywords: Pearl River Delta region; Volatile organic compounds; Oxygenated volatile organic compounds; Alkyl nitrate aging determination; Ozone formation potential;

Systematic evaluation of ozone control policies using an Ozone Source Apportionment method by Ying Li; Alexis K.H. Lau; Jimmy C.H. Fung; Hui Ma; Yuyu Tse (136-146).
Ground-level ozone is a secondary pollutant that causes serious health and environmental damage. One of the main challenges in controlling ground-level ozone is to identify the categories of ozone precursor species that contribute the most to ozone levels, and the regions from which they are emitted. In this study, we apply a photochemical model source apportionment tool to identify the contributions of various precursors to seasonal ozone levels in Hong Kong (HK) and the Pearl River Delta (PRD) region, according to their source regions and categories. We establish a full precursor contribution matrix for the ozone concentrations in all cities within the HK/PRD region. This matrix can be used to rank the relative importance of precursors by source region/category for each city. It can also be used to show how the precursor emissions from any city/category affect ozone levels in neighboring cities. The results show substantial seasonal variation in the source contributions from the HK/PRD region. During ozone episodes, precursors from the region accounted for 68–80% of ozone concentrations in July and 35–55% in October, but only 19–32% in January and April. For all of the cities in the PRD, the top three precursor categories contributing to ozone episodes were mobile, point and area sources. Biogenic and point sources were more important in July than in October. In contrast, the ranking of contributing source regions showed considerable variation across cities and seasons, implying substantial variations in the ways in which precursors from one city affect ozone levels in neighboring cities. Our results show that source contribution and impact analysis can be very useful for evaluating the ozone control strategies of local governments. For the PRD region, a local reduction in mobile, area and point sources, together with regional collaborations on pollution control, are of particular importance in effectively reducing episodic ozone concentrations.► Four monthly CAMx simulation of O3 for the PRD (Jan, Apr, Jul and Oct) were analyzed. ► OSAT used to analyze the source/impact relationships amongst cities by source type/region. ► Mutual impact of O3 episodes amongst cities in PRD varies greatly by season. ► GZ sources are impacting itself and other cities greatly, particularly its mobile sources. ► HK sources have smaller local impact, but impact downwind cities substantially.
Keywords: MM5; CAMx; Ozone control; Source sectors; Ozone Source Apportionment Technology; PRD;

A study of control policy in the Pearl River Delta region by using the particulate matter source apportionment method by Dongwei Wu; Jimmy Chi Hung Fung; Teng Yao; Alexis Kai Hon Lau (147-161).
In recent years, Mainland China, and in particular the industrial hotbed of the Pearl River Delta (PRD) has experienced an increasingly serious problem of high concentrations of airborne particulate matter. Following the tightening-up of China's air quality policies in recent years, and with especially fine particles now added to a new air quality objective, the identification of major source regions and major types of pollutants has become crucial. In this study, the Comprehensive Air Quality Model (CAMx), together with the Particulate Source Apportionment Technology (PSAT) source apportionment method, has been applied to analyze how different emission activities influence PM concentration in the PRD region. By using this method, a detailed source region and emission category contribution matrix is derived for all regions within the Hong Kong/PRD region and source appointment results show that, on average, for different cities super-regional transport and mobile vehicles are the two major fine particle sources, contributing 62% (34.3 μg m−3) and 21% (12.2 μg m−3) of the total figure in December, and 42% (13.1 μg m−3) and 28% (9.7 μg m−3) in April. Meanwhile, over the same period in Hong Kong, in addition to these two factors, marine proved another very significant source of particle pollutant, amounting to 18% of the total figure (4.7 μg m−3). Another important cause of high PM levels has been the transport of fine particles between cities within the PRD region, with three different regions selected for detailed analysis. Results show that for the Hong Kong/PRD region local reduction of mobile sources and collaboration between different areas could have succeeded in alleviating the air pollution problem.► We use CAMx to simulate air quality in PRD regions. ► A particulate source apportionment method is applied in the PRD regions. ► Mobile emission is one of the major emission contributors to PM2.5. ► Collaboration on emission reduction between different regions is important.
Keywords: CAMx; PSAT; Hong Kong; PRD; Category;

For the purpose of systematically characterizing the ambient volatile organic compound (VOC) levels and their emission sources in the Pearl River Delta (PRD) of China, a grid study with VOC samples simultaneously taken at 84 sites over the PRD was conducted in summer and winter of 2008 and 2009. Positive Matrix Factorization (PMF) model was applied to identify the major VOC contributing sources and their temporal and spatial variations. Nine sources were identified, with gasoline exhaust, industrial emission and LPG leakage & propellant emission the top three significant sources. They accounted for 23%, 16% and 13% of the ambient VOC levels, respectively. Control measures should be therefore targeted on mitigating the VOC emissions from the traffic-related and industrial-related sources. The total VOC level did not show strong increase from 5 a.m. to 10 a.m. during all the four sampling campaigns, which may result from stronger wind and higher mixing height at 10 a.m. Three hotspot areas with significant VOC contributions were identified by source apportionment analysis: (1) the Pearl River Estuary; (2) an area from Central Dongguan to North Shenzhen; and (3) the Zhuhai–Zhongshan–Jiangmen area. For better characterizing the roles of VOC and NO x in producing the secondary pollutants and to identify specific sources emitting excessive concentrations of precursors, the emission-oriented Photochemical Assessment Monitoring Station (PAMS) network is recommended to be established in the PRD. Three PAMS networks are suggested in correspondence to the three identified hotspot areas.► A grid study was initiated with VOC samples simultaneously taken at 84 sites over the PRD. ► PMF model was applied to identify major VOC sources and their spatiotemporal variations. ► Hotspot areas with significant VOC contributions were identified over the PRD. ► Emission-oriented monitoring network, such as PAMS, is recommended to establish in the PRD.
Keywords: Volatile organic compounds; Positive matrix factorization; Photochemical assessment monitoring station; Pearl River Delta;

Semi-volatile organic compounds (SVOCs) air pollution caused by municipal garbage compressing process was investigated at a garbage compressing station (GCS). The most abundant contaminants were phthalate esters (PAEs), followed by polycyclic aromatic hydrocarbons (PAHs) and organic chlorinated pesticides (OCPs). ∑16PAHs concentrations ranged from 58.773 to 68.840 ng m−3 in gas and from 6.489 to 17.291 ng m−3 in particulate phase; ∑20OCPs ranged from 4.181 to 5.550 ng m−3 and from 0.823 to 2.443 ng m−3 in gas and particulate phase, respectively; ∑15PAEs ranged from 46.498 to 87.928 ng m−3 and from 414.765 to 763.009 ng m−3 in gas and particulate phase. Lung-cancer risk due to PAHs exposure was 1.13 × 10−4. Both non-cancer and cancer risk levels due to OCPs exposure were acceptable. Non-cancer hazard index of PAEs was 4.57 × 10−3, suggesting safety of workers as only exposure to PAEs at GCS. At pilot scale, 60.18% of PAHs, 70.89% of OCPs and 63.2% of PAEs were removed by an integrated biotrickling filter-photocatalytic reactor at their stable state, and health risk levels were reduced about 50%, demonstrating high removal capacity of integrated reactor.► TSP and model SVOCs emitted during garbage compressing process were monitored. ► Model was used to describe gas-particle partitioning of target SVOCs. ► BTF-PC integrated reactor was employed for SVOCs pollution control. ► Health risk of target SVOCs were assessed before and after treatment.
Keywords: Atmospheric SVOCs; Contamination level; Garbage compressing station; Gas-particle partition; Health risk; Removal efficiency;

Comparison of particle number size distributions and new particle formation between the urban and rural sites in the PRD region, China by D.L. Yue; M. Hu; Z.B. Wang; M.T. Wen; S. Guo; L.J. Zhong; A. Wiedensohler; Y.H. Zhang (181-188).
Particle number size distributions were simultaneously measured at the Guangzhou (GZ) urban site (23.13°N, 113.26°E) and the Back-garden (BG) rural site (23.5°N, 113.03°E) in the Pearl River Delta (PRD) region in July, 2006. It provided new findings into the evolution of particle number size distribution and new particle formation (NPF) in two different environments. Number concentration of particles (20 nm–10 μm diameter) at GZ was about 70% higher than at BG and significantly affected by traffic emission. However, number concentrations of the regional aerosols (100–660 nm) were (6 ± 3) × 103 cm−3 at both sites. At BG, the diurnal variation of particle number size distributions showed an obvious particle growth process beginning at about 9:00 (LT), probably caused by NPF. In contrast, particle number concentrations in the size rages of 20–45 nm, 45–100 nm, and 100–660 nm showed similar trends with two main peaks at about 12:00 (LT) and 19:00 (LT) at GZ. NPF events were observed at both sites, but the occurrence frequency at GZ was about 50% lower than at BG. Regional NPF events at both sites probably in the same air mass were simultaneously observed with similar growth rates, concentrations and production rates of the condensable vapors, and condensational sinks on July 6. On the whole, deceasing traffic emission will improve air quality efficiently in the aspect of particle number concentration and fine particulate pollution in the summer of PRD should be controlled in a regional scale, especially with stagnant air mass from South China Sea.► Evolution of particle size distribution in two different environments was provided. ► A regional NPF event simultaneously observed at urban and rural sites was reported. ► The diurnal variations of particle number size distributions were compared. ► Relation of particle number size distributions with air mass history was discussed.
Keywords: Number size distribution; Particle number concentration; Regional pollution; New particle formation;

Emission inventory of carbonaceous pollutants from biomass burning in the Pearl River Delta Region, China by Yisheng Zhang; Min Shao; Yun Lin; Shengji Luan; Ning Mao; Wentai Chen; Ming Wang (189-199).
Emissions from burning major agricultural residue were measured through laboratory simulations using a self-designed dilution chamber system. Emission factors of CO2, CO, non-methane hydrocarbons (NMHCs), oxygenated volatile organic compounds (OVOCs), PM10, PM2.5, OC and EC in PM2.5 were measured for burning rice straw in flaming and smoldering combustion, and for burning of sugarcane leaves. NMHCs emitted from crop straw open burning were dominated by C2 hydrocarbons (ethene, ethane, ethyne), contributing (53.4 ± 4.6)% in volume in rice straw burning emissions and 41.8% in sugarcane burning emissions, respectively. Acetone and aldehyde were major OVOCs species in open straw burning emissions. A survey was conducted to determine the fraction of field crop biomass burned during harvesting season and the amounts of household firewood and crop residue consumption in 2008. Information obtained from the survey, together with measured EFs for field burning of rice straw and sugarcane, and EFs from literatures for field burning of other agricultural residues, biofuel combustion and forest fires, were used in developing the source inventories of carbonaceous pollutants in the PRD region. The annual emissions of CO, VOCs (including NMHCs and OVOCs), NO x , PM2.5, OC and EC from burning biomass were estimated to be 186.38, 15.94, 4.93, 15.56, 7.10, 2.25 kt in the year 2008, respectively. These estimates are lower than previously published estimates by 23–63%. Open burning patterns (flaming and smoldering) and rural biofuel use contribute to the differences. Field burning of straw contributed mainly to VOCs, PM2.5 and OC emissions while the residential sector was the dominant source of EC, CO and NO x . The contributions of biomass burning to entire PRD emissions are estimated as 3.37–6.53%, respectively, for PM, and 1.82–3.17%, respectively, for VOCs, and 0.52–2.77%, respectively, for NO x .Field burning dominated by smoldering pattern in summer in the PRD.Display Omitted► Emissions from burning crop straws were measured by self-designed chamber system. ► Surveys were conducted to determine biomass burning activity in the PRD region. ► A highly resolved PRD regional biomass burning emission inventory was established. ► Contributions of biomass burning emissions to entire PRD emissions were calculated.
Keywords: Biomass burning; Emission factor; Chamber; Emission inventory; Regional allocation;

Sources of secondary organic aerosols in the Pearl River Delta region in fall: Contributions from the aqueous reactive uptake of dicarbonyls by Nan Li; Tzung-May Fu; Junji Cao; Shuncheng Lee; Xiao-Feng Huang; Ling-Yan He; Kin-Fai Ho; Joshua S. Fu; Yun-Fat Lam (200-207).
We used the regional air quality model CMAQ to simulate organic aerosol (OA) concentrations over the Pearl River Delta region (PRD) and compared model results to measurements. Our goals were (1) to evaluate the potential contribution of the aqueous reactive uptake of dicarbonyls (glyoxal and methylglyoxal) as a source of secondary organic aerosol (SOA) in an urban environment, and (2) to quantify the sources of SOA in the PRD in fall. We improved the representation of dicarbonyl gas phase chemistry in CMAQ, as well as added SOA formation via the irreversible uptake of dicarbonyls by aqueous aerosols and cloud droplets, characterized by a reactive uptake coefficient γ = 2.9 × 10−3 based on laboratory studies. Our model results were compared to aerosol mass spectrometry (AMS) measurements in Shenzhen during a photochemical smog event in fall 2009. Including the new dicarbonyl SOA source in CMAQ led to an increase in the simulated mean SOA concentration at the sampling site from 4.1 μg m−3 to 9.0 μg m−3 during the smog event, in better agreement with the mean observed oxygenated OA (OOA) concentration (8.0 μg m−3). The simulated SOA reproduced the variability of observed OOA (r = 0.89). Moreover, simulated dicarbonyl SOA was highly correlated with simulated sulfate (r = 0.72), consistent with the observed high correlation between OOA and sulfate (r = 0.84). Including the dicarbonyl SOA source also increased the mean simulated concentrations of total OA from 8.2 μg m−3 to 13.1 μg m−3, closer to the mean observed OA concentration (16.5 μg m−3). The remaining difference between the observed and simulated OA was largely due to impacts from episodic biomass burning emissions, but the model did not capture this variability. We concluded that, for the PRD in fall and outside of major biomass burning events, 75% of the total SOA was biogenic. Isoprene was the most important precursor, accounting for 41% of the total SOA. Aromatics accounted for 13% of the total SOA. Our results show that the aqueous chemistry of dicarbonyls can be an important SOA source, potentially accounting for 53% of the total surface SOA in the PRD in fall.► CMAQ model performance enhanced with addition of dicarbonyl SOA source. ► 75% of total SOA was biogenic for the PRD in fall and isoprene was the most important precursor. ► The irreversible uptake of dicarbonyls by aqueous particles was an important SOA formation pathway in the PRD in fall.
Keywords: Secondary organic aerosol; Glyoxal; Methylglyoxal; CMAQ; Pearl River Delta (PRD);

Establishing a conceptual model for photochemical ozone pollution in subtropical Hong Kong by Z.H. Ling; H. Guo; J.Y. Zheng; P.K.K. Louie; H.R. Cheng; F. Jiang; K. Cheung; L.C. Wong; X.Q. Feng (208-220).
Photochemical ozone (O3) formation is related to its precursors and meteorological conditions. A conceptual model of O3 air pollution is developed based on the analysis of data obtained at Tung Chung (TC) in Hong Kong. By comparing meteorological parameters between O3 and non-O3 episode days, it was found that high temperatures, strong solar radiation, low wind speeds and relative humidity, northeasterly and/or northwesterly prevailing winds were favorable for the O3 formation, while tropical cyclones were most conducive to the occurrence of O3 episodes. Backward trajectories simulation and graphical illustration of O3 pollution suggested that super-regional (i.e. central and eastern China) and regional (i.e. Pearl River Delta, southern China) transport was another factor that contributed to high O3 levels in Hong Kong. The photochemical O3 formation, generally VOC-limited in Hong Kong, was controlled by a small number of volatile organic compounds (VOCs). Furthermore, the positive matrix factorization (PMF) simulation suggested that solvent usage and vehicular emissions are the major contributors to ambient VOCs in Hong Kong. Finally, this paper presents recommendations for further O3 research and implementation of O3 control strategies.► A conceptual model is for the first time developed for ozone for Hong Kong. ► Tropical cyclones are most conducive to the occurrence of high O3 episodes. ► Super-regional and regional transports are other factors that contribute to high O3 levels in Hong Kong.
Keywords: Conceptual model; Ozone; Regional; Super-regional; Hong Kong;

Evaluating the uncertainties of thermal catalytic conversion in measuring atmospheric nitrogen dioxide at four differently polluted sites in China by Zheng Xu; Tao Wang; L.K. Xue; Peter K.K. Louie; Connie W.Y. Luk; J. Gao; S.L. Wang; F.H. Chai; W.X. Wang (221-226).
A widely used method for measuring nitrogen dioxide (NO2) in the atmosphere is the conversion of NO2 to nitric oxide (NO) on the hot surface of a molybdenum oxide (MoO) catalyst followed by the chemiluminescence detection of NO. Although it has long been recognized that this type of conversion may suffer from the positive interference of other oxidized nitrogen compounds, evaluations of such interference in the atmosphere are scarce, thus rendering it difficult to make use of a large portion of the NO2 or NO x data obtained via this method (often denoted as NO2* or NO x *). In the present study, we compared the MoO converter with a selective, more accurate photolytic approach at four differently polluted sites in China. The converter worked well at the urban site, which was greatly affected by fresh emissions, but, on average, overestimated NO2 by 30%–50% at the two suburban sites and by more than 130% at the mountain-top site during afternoon hours, with a much larger positive bias seen during the top 10% of ozone events. The degree of overestimation depended on both air-parcel age and the composition of the oxidation products/intermediates of NO x (NO z ). We attempted to derive an empirical formula to correct for this overestimation using concurrently measured O3, NO, and NO2* at the two suburban sites. Although the formula worked well at each individual site, the different NO z partitions at the sites made it difficult to obtain a universal formula. In view of the difficulty of assessing the uncertainties of the conventional conversion method, thus limiting the usability of data obtained via this method in atmospheric research, we suggest that, in areas away from fresh NOx emission sources, either a more selective NO2 measurement method or a NO y (NO x and its reaction products and intermediates) instrument should be adopted.► MoO and photolytic converters for measuring NO2 were compared at four field sites. ► Overestimation of NO2 by the MoO converter ranged from 6% to 280%. ► The overestimation depended on both air-parcel age and composition of NO z . ► A ‘true’ NO2 or a NO y system is recommended for areas away from fresh NO x emission sources.
Keywords: Nitrogen dioxide; Molybdenum oxide converter; Photolytic converter; Air-parcel age; NO z ;

A numerical study of the impact of climate and emission changes on surface ozone over South China in autumn time in 2000–2050 by Q. Liu; K.S. Lam; F. Jiang; T.J. Wang; M. Xie; B.L. Zhuang; X.Y. Jiang (227-237).
Using the Weather Research and Forecasting Model with Chemistry (WRF/Chem) model, we conducted a series of numerical experiments to investigate the relative contributions of climate and emission change to surface ozone (O3) over South China for the period of October in 2005–2007 and 2055–57. WRF/Chem was driven by the outputs of Community Climate System Model version 3 (CCSM3). The simulations predict that on average near-surface temperature and water vapor mixing ratio are projected to increase 1.6 °C and 1.6 g kg 1 under A1B scenario. In response to the climate change, the emissions of isoprene and monoterpenes in South China increase by 5–55% and 5–40%, respectively. The change of climate and biogenic emission can result in a change of −5 to 5 ppb of afternoon surface O3 mixing ratios, with an average of 1.6 ppb over the land region in South China. Over Pearl River Delta, a region of dense network of cities, the 2000–2050 climate changes increase afternoon mean surface O3 by 1.5 ppb. The change of anthropogenic emission can result in a change of −3–24 ppb of afternoon surface O3 mixing ratios, with an average of 12.8 ppb over the land region in South China. Our analysis suggests that the anthropogenic emissions have greater impact on the change of surface O3 concentration over South China compared to climate change. The combined effect of climate and emission can increase afternoon mean surface O3 over South China by an average of 18.2 ppb in the land region, with the highest increase up to 24 ppb occurring over southeast of Hunan province.► Impact on surface ozone due to climate change in PRD Region was studied using WRF-Chem. ► Near-surface temperature is projected to increase 1.6 °C under A1B scenario. ► Emissions of isoprene and monoterpenes in South China increase by 5–55% and 5–40%. ► Climate change and biogenic emission increase cause +1.6 ppb of surface ozone over land in 2050. ► Anthropogenic emission increase cause +12.8 ppb of surface ozone over land in 2050.
Keywords: Ozone; WRF/Chem; Climate change; Biogenic emission; Anthropogenic emission; South China;