Pearl River Delta Regional Air Research Articles

Characteristics and Meteorological Factors of Complex Nonattainment Pollution of Atmospheric Photochemical Oxidant (Ox) and PM2.5 in the Pearl River Delta Region, China

Based on the atmospheric pollutant data from twelve monitoring sites in the Guangdong-Hong Kong-Macao Pearl River Delta Regional Air Quality Monitoring Network, the mass concentration trends of atmospheric photochemical oxidants (Ox, NO2+O3) and PM2.5 during 2013-2017 were studied. The complex nonattainment pollution of Ox and PM2.5 is defined as the daily average mass concentration of NO2 and PM2.5 and daily maximum 8 h average (O3 MDA8) mass concentration of O3 simultaneously that exceeds the Chinese grade Ⅱ national air quality standard. The characteristics and meteorological factors that influence the complex nonattainment pollution of Ox and PM2.5 at different types of areas were analyzed. The results indicate that from 2013 to 2017, the annual average mass concentration of PM2.5 in the Pearl River Delta (PRD) region decreased from (44±7) μg·m-3 to (32±4) μg·m-3, which met the annual standard for three consecutive years. The annual average mass concentration of Ox decreased from (127±14) μg·m-3 in 2013 to (114±12) μg·m-3 in 2016 and then showed a general rebound trend to (129±13) μg·m-3 in 2017 when O3 concentrations increased significantly (10 μg·m-3). The proportion of pollution processes with O3 as the primary pollutant increased from 33% in 2013 to 78% in 2017, and the regional characteristics of simultaneous pollution in multiple cities have been highlighted. The complex nonattainment pollution of Ox and PM2.5 occurred 60 times during the study period, primarily in urban sites (78%) and suburban sites (22%). The largest number of days of complex nonattainment pollution occurred in autumn (52%) because of strong solar radiation that was conducive to ozone formation, and consequently, the high oxidization of the atmosphere promoted the secondary generation of PM2.5. The weather conditions that caused the complex nonattainment pollution in the PRD mainly include outflow-high-pressures (43%), subtropical-high-pressures(30%), and tropical-depressions (27%). In terms of specific meteorological conditions, when the temperature was in the range of 20-25℃ and relative humidity was in the range of 60%-75%, the proportion of complex nonattainment pollution was the highest (22%). When O3 pollution was substantial, the high relative humidity and low wind speed during the nighttime caused the concentration of NO2 and PM2.5 to rise significantly, and then the high temperatures during the day aggravated the complex nonattainment pollution.

Impact of Ozone Pollution on Human Health and Economic Loss Assessment

The problem of ozone (O₃) pollution in the air has become increasingly prominent in recent years, and the health effects of O₃ pollution on people have attracted more attention. O₃ is the primary pollutant with the highest over-limit rate in the Guangdong-Hong Kong-Macao Pearl River Delta. Based on the data of O₃ concentration, exposed pollution, baseline mortality, and hospitalization rate monitored by the Pearl River Delta Regional Air Quality Monitoring Network (PRD-RAQMN) in Shenzhen. This study evaluates the impact of O₃ pollution on human health and economic loss in Shenzhen from 2006 to 2018 by using the relative risk model, benefit conversion method, and disease cost method. The annual mean value of daily 8 h maximum concentration of O₃ in Shenzhen shows an overall significant upward trend from 2006 to2018, with an average annual value range of 70 to 190.92 μg/m³ and an average value of 112.89 μg/m³. The number of death and hospitalization caused by O₃ pollution increases significantly, and the incidence of respiratory system diseases is higher than that of circulatory system diseases. However, the mortality caused by circulatory system diseases was higher than that caused by respiratory system diseases. The economic loss of health caused by O₃ pollution increased yearly, with an annual average economic loss of82.46 million RMB, reached 658.31 million RMB in 2018, accounted for 0.0272% of Shenzhen’s GDP in 2018.

Trends of outdoor air pollution and the impact on premature mortality in the Pearl River Delta region of southern China during 2006–2015

Severe air pollution in the Pearl River Delta (PRD) region of southern China has increased attention of both the scientific community and policy makers. Air quality data collected at the PRD Regional Air Quality Monitoring Network during 2006–2015 were analyzed for assessing the effectiveness of pollution control measures and for estimating the trends of premature mortality attributable to ambient PM2.5 and O3. Statistically significant decreasing trends were detected for PM2.5 (−1.74 to −1.83 μg m−3 yr−1), PM10 (−2.70 to −2.78 μg m−3 yr−1), NO (−0.61 to −0.74 μg m−3 yr−1), NO2 (−1.20 to −1.22 μg m−3 yr−1), and SO2 (−3.46 to −4.01 μg m−3 yr−1), while an increasing trend was found for O3 (0.70–0.86 μg m−3 yr−1) during the study period. The findings demonstrate the effectiveness of control measures implemented in the last decade for primary pollutants and also indicate the challenges for controlling secondary pollutants. The PM2.5-related premature deaths varied little, e.g., from 40.6 thousand deaths in 2006 to 40.4 thousand deaths in 2015, due to the two contrasting factors, i.e., the decreased PM2.5 concentration and increased population. The increases in both O3 concentration and exposed population resulted in a significant rising trend for the O3-related premature deaths, which increased from 2.7 thousand deaths in 2006 to 4.5 thousand deaths in 2015, at a rate of 165 deaths yr−1. Consistent with the spatial distribution of air pollution and population density, high levels of premature deaths from PM2.5 and O3 were located in the central PRD including Guangzhou, Foshan, Dongguan, and Shenzhen. Decreasing PM2.5 concentration is the most effective way in reducing the regional mortality burden from air pollution in the near future. Besides controlling primary emissions of PM2.5, reducing VOCs emissions is also important for limiting atmospheric oxidizing capacity and associated secondary PM2.5 formation.

Institutional obstacles and opportunities for policy entrepreneurship in cross-border environmental management: a case study in China’s Greater Pearl River Delta region

ABSTRACTAir pollution was placed very low on China's policy agenda in the 1990s. Sharing the PRD's Southern border, Hong Kong became increasingly concerned with the pollution originating from their rapidly developing neighbors. This paper offers an explanatory study for the implementation of a trans-boundary air quality monitoring network in 2005 which was, in many ways, considered a breakthrough in environmental cooperation in this region. Empirical evidence demonstrates that extended efforts from a Hong Kong official had eventually triggered the Guangdong provincial government and the Hong Kong government to undertake a range of collaborative measures to improve regional air quality, including the establishment of the Pearl River Delta regional air quality monitoring network in 2005. Building upon the concept of “policy entrepreneurship,” this study discovers that the policy entrepreneur's political rank endowed him with direct access to the formal cross-border institution, through which he was able to build a close professional relationship with his mainland counterparts and enables him to be a transfer agent. This case illustrates that state actors are well-placed in this region's trans-boundary platforms to initiate the transfer of policy innovations to neighboring governments, which prompts the formulation of cooperative projects. Nonetheless, this paper also cautions that effective cross-border collaboration is still largely dependent upon the contextual framework of the authoritarian governance regime whereby the interactions between policymakers and implementers are fundamentally shaped by institutional design and incentives.

Development of a custom OMI NO<sub>2</sub> data product for evaluating biases in a regional chemistry transport model

Abstract. In this paper, we present the custom Hong Kong NO2 retrieval (HKOMI) for the Ozone Monitoring Instrument (OMI) on board the Aura satellite which was used to evaluate a high-resolution chemistry transport model (CTM) (3 km × 3 km spatial resolution). The atmospheric chemistry transport was modelled in the Pearl River Delta (PRD) region in southern China by the Models-3 Community Multiscale Air Quality (CMAQ) modelling system from October 2006 to January 2007. In the HKOMI NO2 retrieval, tropospheric air mass factors (AMFs) were recalculated using high-resolution ancillary parameters of surface reflectance, a priori NO2 and aerosol profiles, of which the latter two were taken from the CMAQ simulation. We tested the influence of the ancillary parameters on the data product using four different aerosol parametrizations. Ground-level measurements by the PRD Regional Air Quality Monitoring (RAQM) network were used as additional independent measurements. The HKOMI retrieval increases estimated tropospheric NO2 vertical column densities (VCD) by (+31 ± 38)%, when compared to NASA's standard product (OMNO2-SP), and improves the normalized mean bias (NMB) between satellite and ground observations by 26 percentage points from −41 to −15%. The individual influences of the parameters are (+11.4 ± 13.4)% for NO2 profiles, (+11.0 ± 20.9)% for surface reflectance and (+6.0 ± 8.4)% for the best aerosol parametrization. The correlation coefficient r is low between ground and satellite observations (r = 0.35). The low r and the remaining NMB can be explained by the low model performance and the expected differences when comparing point measurements with area-averaged satellite observations. The correlation between CMAQ and the RAQM network is low (r ≈ 0.3) and the model underestimates the NO2 concentrations in the northwestern model domain (Foshan and Guangzhou). We compared the CMAQ NO2 time series of the two main plumes with our best OMI NO2 data set (HKOMI-4). The model overestimates the NO2 VCDs by about 15% in Hong Kong and Shenzhen, while the correlation coefficient is satisfactory (r = 0.56). In Foshan and Guangzhou, the correlation is low (r = 0.37) and the model underestimates the VCDs strongly (NMB = −40%). In addition, we estimated that the OMI VCDs are also underestimated by about 10 to 20% in Foshan and Guangzhou because of the influence of the model parameters on the AMFs. In this study, we demonstrate that the HKOMI NO2 retrieval reduces the bias of the satellite observations and how the data set can be used to study the magnitude of NO2 concentrations in a regional model at high spatial resolution of 3 × 3 km2. The low bias was achieved with recalculated AMFs using updated surface reflectance, aerosol profiles and NO2 profiles. Since unbiased concentrations are important, for example, in air pollution studies, the results of this paper can be very helpful in future model evaluation studies.

Regional Air Quality Management in China: A Case Study in the Pearl River Delta

The current jurisdiction-based environmental management paradigm is deficient to address China's growing regional air pollution problems. Based on the foreign management experiences, the “1+N” regional air quality management mode with Chinese characteristics is proposed, which combines the bottom-up and top-down management features among superior and local governments, to cope with the regional air pollution. Several crucial principles are discussed accordingly. In the case study in Pearl River Delta (PRD) region, the PRD Regional Air Quality Management Committee and the Center of Regional Atmospheric Science are carefully designed and are now serving as decision-making body and scientific support agency, respectively. The encouraging practice in the PRD region yields important hints for China's regional air pollution control policy making.

Importance of NOx control for peak ozone reduction in the Pearl River Delta region

As major air pollutants and key precursors of several secondary air pollutants, nitrogen oxide (NOx) emissions are regulated in many countries. However, NOx control increases ozone concentrations when the ozone formation regime is volatile organic compound (VOC) limited. Although many studies have shown that NOx regulation reduces ozone levels over the long term, it is still of concern that NOx regulation increases short‐term ozone levels in metropolitan regions, where ozone formation is found to be predominantly VOC‐limited. The Pearl River Delta (PRD) in China is such a region. Our modeling sensitivity study shows that while NOx reduction in the PRD region may raise the mean ozone concentration, it can also decrease peak ozone levels. Similar changes are observed in the NOx and ozone data of the PRD regional air quality monitoring network (2006–2012), lending further credence to our results. In the model, this NOx control effect is a result of the complicated spatial and diurnal variations of the ozone formation regime. In most of the PRD region, the formation regime is VOC‐limited in the morning and becomes NOx‐limited during peak ozone hours. Although some areas are always VOC‐limited, their ozone concentrations are relatively low, and the ozone increases caused by NOx reduction generally do not cause higher ozone levels than the region's original ozone maxima. Several control scenarios are simulated to evaluate the effects of various possible control regulations. Our results show that in addition to VOC control, NOx control can be effective for reducing peak ozone concentrations in the PRD region.

The Pearl River Delta Regional Air Quality Monitoring Network - Regional Collaborative Efforts on Joint Air Quality Management

The Guangdong and Hong Kong governments have collaboratively established the first Pearl River Delta regional air quality monitoring network (“PRD RAQMN”) since November 2005 which represented the first joint air quality monitoring of the regional air pollution and reporting efforts at a rapidly developed and heavy-polluted area in the southern China. The PRD RAQMN keeps track on the long-term evolution of air pollution status in the PRD region located in the south coast of China. It recorded the air quality trend during the 11th Five-Year Plan (FYP) implemented between 2006 and 2010, and the years of synchronous of leapfrogging economic development and stringent emission control on coal-fired power plants and vehicles for the 12th FYP to be implemented between 2011 and 2015. The PRD RAQMN showcases as a role model for the cooperation of local administrative authorities and also serves the surveillance system for joint prevention and management of air pollution. The PRD RAQMN catalyzed the cooperation among regions in the nation and public dissemination of air quality information which is otherwise under tight scrutiny in the past. The PRD RAQMN demonstrates that the regional collaboration and formation of consortium is critical in air quality management strategy to address and resolve the air pollution problems in China more effectively.

Characterization and source apportionment of submicron aerosol with aerosol mass spectrometer during the PRIDE-PRD 2006 campaign

Abstract. Size-resolved chemical compositions of non-refractory submicron aerosol were measured using an Aerodyne quadrupole aerosol mass spectrometer (Q-AMS) at the rural site Back Garden (BG), located ~50 km northwest of Guangzhou in July 2006. This paper characterized the submicron aerosol particles of regional air pollution in Pearl River Delta (PRD) in the southern China. Organics and sulfate dominated the submicron aerosol compositions, with average mass concentrations of 11.8 ± 8.4 μg m−3 and 13.5 ± 8.7 μg m−3, respectively. Unlike other air masses, the air masses originated from Southeast-South and passing through the PRD urban areas exhibited distinct bimodal size distribution characteristics for both organics and sulfate: the first mode peaked at vacuum aerodynamic diameters (Dva) ∼200 nm and the second mode occurred at Dva from 300–700 nm. With the information from AMS, it was found from this study that the first mode of organics in PRD regional air masses was contributed by both secondary organic aerosol formation and combustion-related emissions, which is different from most findings in other urban areas (first mode of organics primarily from combustion-related emissions). The analysis of AMS mass spectra data by positive matrix factorization (PMF) model identified three sources of submicron organic aerosol including hydrocarbon-like organic aerosol (HOA), low volatility oxygenated organic aerosol (LV-OOA) and semi-volatile oxygenated organic aerosol (SV-OOA). The strong correlation between HOA and EC indicated primary combustion emissions as the major source of HOA while a close correlation between SV-OOA and semi-volatile secondary species nitrate as well as between LV-OOA and nonvolatile secondary species sulfate suggested secondary aerosol formation as the major source of SV-OOA and LV-OOA at the BG site. However, LV-OOA was more aged than SV-OOA as its spectra was highly correlated with the reference spectra of fulvic acid, an indicator of aged and oxygenated aerosol. The origin of HOA and OOA (the sum of LV-OOA and SV-OOA) has been further confirmed by the statistics that primary organic carbon (POC) and secondary organic carbon (SOC), estimated by the EC tracer method, were closely correlated with HOA and OOA, respectively. The results of the EC tracer method and of the PMF model revealed that primary organic aerosol (POA) constituted ~34–47 % of OA mass and secondary organic aerosol (SOA) constituted ~53–66 % of regional organic aerosol in PRD during summer season. The presence of abundant SOA was consistent with water soluble organic carbon (WSOC) results (accounting for ~60 % of OC on average) by Miyazaki et al. (2009) for the same campaign. OOA correlated well with WSOC at the BG site, indicating that most OOA were water soluble. More specifically, approximately 86 % of LV-OOA and 61 % of SV-OOA were estimated as water soluble species on the basis of carbon content comparison.

Development of an emission processing system for the Pearl River Delta Regional air quality modeling using the SMOKE model: Methodology and evaluation

Abstract An emission pre-processing tool is generally needed to transform a bulk annual emission inventory into gridded, temporal (monthly, weekly, and hourly), and speciated emissions in order to use complex air quality models such as the Community Multi-scale Air Quality (CMAQ) model to assess control strategies, forecast air quality, and investigate pollution formation and transport processes. To support the regional air quality modeling in the Pearl River Delta (PRD), we developed an emission pre-processing system, Sparse Matrix Operator Kernel Emissions-PRD (SMOKE-PRD), based on the U.S. Environmental Protection Agency (USEPA)/SMOKE model. This paper introduces the methods and procedures for adapting the SMOKE model to the PRD regional bulk emissions. These include the compilation of the PRD local source-class clarification codes, the incorporation of the PRD local emission inventory, and the updating of spatial, temporal, and chemical speciation information. The SMOKE-PRD system was evaluated, and a case study on ozone simulation was conducted to demonstrate the applicability of the SMOKE-PRD system. Results show that the model can properly simulate temporal variations, spatial patterns, and peak values of O3 concentrations in the PRD region, suggesting the SMOKE-PRD system was successfully localized and can be used to provide model-ready emissions for regional air quality modeling in the PRD region. This work can be extended for adapting the SMOKE model to process emissions for modeling use in other regions of China.

Assessment of motor vehicle emission control policies using Model-3/CMAQ model for the Pearl River Delta region, China

Abstract In recent decades, the Pearl River Delta (PRD) region located in south China has been experiencing severe air pollution, arising from the rapid increase in industry and motor vehicles. As a major contributing source to VOCs and NO x emissions, control of vehicular emissions plays a very important role in improving regional air quality. By taking 2015 as a target year, this paper assessed the impacts of five possible motor vehicle emission control measures and a combined policy scenario on ambient air quality in the PRD region, with the use of the Model-3/CMAQ (Community Multi-scale Air Quality) model. The results show: (1) an overall decreasing pattern in SO 2 , NO 2 and PM 10 concentrations was found in central-south metropolitan areas of the PRD region for all measures, but increased O 3 concentrations may occur in these areas as well. The exception to this is that a slight decrease was observed for the cases of motorcycle restriction and introduction of HEV; (2) upgrading to National IV emission standards is the most effective individual measure and can reduce daily averaged NO 2 and PM 10 concentrations by 11.7 ppbV and 21.3 μg m −3 , respectively; but involves an increase (at maximum) of 10.3ppbV in O 3 concentration. Evaluation of the combined scenario indicates that solely controlling motor vehicle emissions is not sufficient to improve PRD regional air quality significantly. O 3 and PM 10 concentrations under the same VOC/NO x reduction ratios exhibit differently at different locations, suggesting that integrated and location-specific pollution control strategies, considering co-control of multi-pollutants, are needed in this region in order to decrease primary and secondary pollutant concentrations simultaneously.

Source origins, modeled profiles, and apportionments of halogenated hydrocarbons in the greater Pearl River Delta region, southern China

We analyze 16‐month data of 13 major halocarbons measured at a southern China coastal site in the greater Pearl River Delta (PRD). A total of 188 canister air samples were collected from August 2001 to December 2002. Overall inspection indicated that CH2Cl2, C2Cl4, and C2HCl3 had similar temporal variations while CFC‐11, CFC‐12, and CFC‐113 showed the same emission patterns during the sampling period. Diurnal variations of halocarbons presented different patterns during ozone episode days, mainly related to emission strength, atmospheric dispersion, and photochemical lifetimes. For further statistics and source appointment, Lagrangian backward particle release simulations were conducted to help understand the potential source regions of all samples and classify them into different categories, including local Hong Kong, inner PRD, continental China, and marine air masses. With the exception of HCFC‐142b, the mixing ratios of all halocarbons in marine air were significantly lower than those in urban and regional air (p < 0.01), whereas no significant difference was found between urban Hong Kong and inner PRD regional air, reflecting the dominant impact of the greater PRD regional air on the halocarbon levels. The halocarbon levels in this region were significantly influenced by anthropogenic sources, causing the halocarbon mixing ratios in South China Sea air to be higher than the corresponding background levels, as measured by global surface networks and by airborne missions such as Transport and Chemical Evolution Over the Pacific. Interspecies correlation analysis suggests that CHCl3 is mainly used as a solvent in Hong Kong but mostly as a feedstock for HCFC‐22 in the inner PRD. Furthermore, CH3Cl is often used as a refrigerant and emitted from biomass/biofuel burning in the inner PRD. A positive matrix factorization receptor model was applied to the classified halocarbon samples in the greater PRD for source profiles and apportionments. Seven major sources were identified and quantified. Emissions from solvent use were the most significant source of halocarbons (71 ± 9%), while refrigeration was the second largest contributor (18 ± 2%). By further looking at samples from the inner PRD and from urban Hong Kong separately, we found that more solvent was used in the dry cleaning industry in Hong Kong, whereas the contribution of cleaning solvent in the electronic industry was higher in the inner PRD. Besides the two common sources of solvent use and refrigeration, the contributions of biomass/biofuel burning and feedstock in chemical manufacturing was remarkable in the inner PRD but negligible in Hong Kong. These findings are of help to effectively control and phase out the emissions of halocarbons in the greater PRD region of southern China.