Qi Fan

Long-term trends of fine particulate matter and chemical composition in the Pearl River Delta Economic Zone (PRDEZ), China

Understanding the trends in PM2.5 levels is essential for formulating clean air plans. This paper analyzes PM2.5 data from various published sources for the years 2000 to 2010 in the Pearl River Delta Economic Zone (PRDEZ). The long-term variation in PM2.5 mass concentration is analyzed. Results show that PM2.5, organic carbon (OC), elemental carbon (EC), and SO42− show a similar trend, increasing before 2005 and then decreasing slightly. The annual average PM2.5 concentration ranges from 49.1 μg·m−3 in 2000 to 64.3 μg·m−3 in 2010, with a peak of 84.1 μg·m−3 in 2004. None of these 11 years meets the new National Ambient Air Quality standard (NAAQS) for PM2.5 (35 μg·m−3). Overall average concentrations of OC, EC, and SO42− are 13.0, 6.5, and 11.8 μg·m−3, respectively. NO3− and NHþ4 respectively have concentrations of 1.5 μg·m−3 and 2.9 μg·m−3 in 2000 and 6.4 μg·m−3 and 5.3 μg·m−3 in 2010, with a statistically significant average annual trend of + 0.2 μg·m−3·yr−1 and + 0.1 μg·m−3·yr−1. In certain geographic regions, OC and EC contribute most of the PM2.5, while in other regions secondary water-soluble ions are more important. In general, OC and SO42− are the dominant components of PM2.5, contributing 20.6% and 18.6%, respectively. These results provide, for the first time, a better understanding of the long-term PM2.5 characteristics and trends, on a species-by-species basis, in the PRDEZ. The results indicate that PM2.5 abatement needs to prioritize secondary species.

Atmospheric nitrogen deposition to forest and estuary environments in the Pearl River Delta region, southern China

Due to its significant ecological and climate consequences, atmospheric nitrogen (N) deposition is a growing global concern, especially in the severely N-polluted regions such as the Pearl River Delta (PRD) region of southern China. One-year measurements of reactive N species, including ammonium nitrogen ( -N), nitrate nitrogen ( -N) and total organic nitrogen (ON) in dry and wet deposition, were conducted using an automated wet–dry sampler incorporated with a DDAS (dry deposition on aqueous surface) sampling device at Dinghushan (DHS), a natural forest site in the northwest of PRD and at Hengmen (HM), an estuary site in the south of PRD during 2006–2007. Total deposition fluxes of N at DHS and HM were up to 48.2 and 37.8 kg ha−1 yr−1, respectively, with most of the deposition occurring in the rainy season. Wet deposition was the dominant form, contributing 65–70% to the total deposition. -N was the largest contributor to the total N deposition at DHS (47%) due to significant influence of agriculture emissions. ON was the most important N component at HM (41%), which is probably attributed to the marine sources. However, -N deposition is increasing rapidly recently and is expected to be more important in the near future. The current N deposition level in PRD is much higher than those in Europe and North America. Great challenges exist in reducing reactive N emission in this region. Thus, a scenario of rising N deposition in PRD in the near future cannot be ruled out. The environmental consequences due to elevated N deposition should therefore be paid more attention in the future.

High time-resolved elemental components in fine and coarse particles in the Pearl River Delta region of Southern China: Dynamic variations and effects of meteorology.

Hourly-resolved PM2.5 and PM10-2.5 samples were collected in the industrial city Foshan in the Pearl River Delta region, China. The samples were subsequently analyzed for elemental components and black carbon (BC). A key purpose of the study was to understand the composition of particulate matter (PM) at high-time resolution in a polluted urban atmosphere to identify key components contributing to extreme PM concentration events and examine the diurnal chemical concentration patterns for air quality management purposes. It was found that BC and S concentrations dominated in the fine mode, while elements with mostly crustal and oceanic origins such as Si, Ca, Al and Cl were found in the coarse size fraction. Most of the elements showed strong diurnal variations. S did not show clear diurnal variations, suggesting regional rather than local origin. Based on empirical orthogonal functions (EOF) method, 3 forcing factors were identified contributing to the extreme events of PM2.5 and selected elements, i.e., urban direct emissions, wet deposition and a combination of coarse mode sources. Conditional probability functions (CPF) were performed using wind profiles and elemental concentrations. The CPF results showed that BC and elemental Cl, K, Fe, Cu and Zn in the fine mode were mostly from the northwest, indicating that industrial emissions and combustion were the main sources. For elements in the coarse mode, Si, Al, K, Ca, Fe and Ti showed similar patterns, suggesting same sources such as local soil dust/construction activities. Coarse elemental Cl was mostly from the south and southeast, implying the influence of marine aerosol sources. For other trace elements, we found vanadium (V) in fine PM was mainly from the sources located to the southeast of the measuring site. Combined with CPF results of S and V in fine PM, we concluded shipping emissions were likely an important elemental emission source.

Impact of a dust storm on characteristics of particle matter (PM) in Guangzhou, China

A strong dust-storm (23–25 April, 2009) occurred in the provinces of Inner Mongolia, Gansu, and Shanxi, North China. Cities along the storm path (from north to south: Xi’ning, Lanzhou, Chengdu, Changsha, and Guangzhou) all experienced a sharp increase in particle matter (PM10) concentration. This is the first case that an Asian dust storm hit Guangzhou in Southern China. The impacts of dust storm on the characteristics of PM were investigated using samples collected in Guangzhou during 27–29 April, 2009. In addition, the mass concentration and chemical composition during a normal non-dust period (12–14 May, 2009) were compared with those in dust period. The results show that the concentration of PM10 during the dust episode (0.231 mg m−3) was twice higher than that in the non-dust episode (0.103 mg m−3). Chemical analysis showed that concentrations of metal elements, enrichment factors of metal elements, and soluble ions during the dust episode were very different from those of non-dust. The total concentration of metal elements content in PM10 was 53.5 μg m−3 in the dust episode, which is about two times higher than that in non-dust episode (28.5 μg m−3). Increases in concentrations of Na, Ti, Zn, Cu, and Cr ranged from zero to 100% during the dust episode. However, the enrichment factors in non-dust episode were higher than that in dust-storm period, indicating that the above five chemicals originated mainly from local sources in Guangzhou. The concentrations of K, Mg, Al, Fe, Mn, V, and Co increased by over 100% in the dust episode, indicating their origins of remote sources. In the dust period, some water-soluble ions increased in PM10, but the main components in PM10 were SO4−, NO3− and NH4+. At last, we assessed the sources of dusts by analyzing synoptic situation and back trajectories of air mass in Guangzhou, and demonstrated that the main source of the dust storm was from Mongolia.

An analysis of aerosol liquid water content and related impact factors in Pearl River Delta.

Aerosol liquid water content (ALWC) has an important effect on atmospheric visibility as well as heterogeneous chemical reactions. In this paper, we used the data size-resolved particle hygroscopic growth factor, and particle number size distribution (PNSD) obtained from H-TDMA and SMPS to compute ALWC at the Guangzhou Panyu site from the winter of 2014 and the spring of 2015. The corresponding results were relatively consistent with the trend for ALWCISO calculated from the ISORROPIA II thermodynamic equilibrium model based on the measurement of aerosol water-soluble ionic compositions obtained from MARGA, with a linear fit yielding an R2 value of 0.76. The fact that ALWCHTDMA was somewhat higher than ALWCISO at low RH values was at least partially attributable to the fact that effects resulting from organic matter hygroscopicity were not taken into account when computing ALWCISO. In sensitivity testing, ambient relative humidity, PNSD and particle hygroscopicity were all found to affect ALWC, in that order. Particles of different modes made different contributions to ALWC with the contributions of nuclear, Aitken, accumulation and coarse modes assessed at <1%, 3%, 85% and 12%, respectively, indicating that the contribution of accumulation mode particles to ALWC dominated among all the aerosol particle modes. During clean processes, decreases in relative humidity and PM2.5 both resulted in a decrease in ALWC. During the pollution processes, calm winds caused local particle accumulation, with ALWC increasing as RH increased. Intraday trends in ALWC and relative humidity were consistent, with minimum mean values observed in the afternoon due to low ambient relative humidity inhibiting an increase in ALWC. However, diurnal variation of aerosol hygroscopicity and ALWC tended to be somewhat anti-correlated, indicating that diurnal changes in aerosol hygroscopicity are not a primary factor resulting in ambient AWLC changes.

Numerical model to quantify biogenic volatile organic compound emissions: The Pearl River Delta region as a case study

This article compiles the actual knowledge of the biogenic volatile organic compound (BVOC) emissions estimated using model methods in the Pearl River Delta (PRD) region, one of the most developed regions in China. The developed history of BVOC emission models is presented briefly and three typical emission models are introduced and compared. The results from local studies related to BVOC emissions have been summarized. Based on this analysis, it is recommended that local researchers conduct BVOC emission studies systematically, from the assessment of model inputs, to compiling regional emission inventories to quantifying the uncertainties and evaluating the model results. Beyond that, more basic researches should be conducted in the future to close the gaps in knowledge on BVOC emission mechanisms, to develop the emission models and to refine the inventory results. This paper can provide a perspective on these aspects in the broad field of research associated with BVOC emissions in the PRD region.

Impact of Refined Land Surface Properties on the Simulation of a Heavy Convective Rainfall Process in the Pearl River Delta Region, China

The location and occurrence time of convective rainfalls have attracted great public concern as they can lead to terrible disasters. However, the simulation results of convective rainfalls in the Pearl River Delta region often show significant discrepancies from the observations. One of the major causes lies in the inaccurate geographic distribution of land surface properties used in the model simulation of the heavy precipitation. In this study, we replaced the default soil and vegetation datasets of Weather Research and Forecasting (WRF) model with two refined datasets, i.e. the GlobCover 2009 (GLC2009) land cover map and the Harmonized World Soil Database (HWSD) soil texture, to investigate the impact of vegetation and soil on the rainfall patterns. The result showed that the simulation patterns of convective rainfalls obtained from the coupled refined datasets are more consistent with the observations than those obtained from the default ones. By using the coupled refined land surface datasets, the overlap ratio of high precipitation districts reached 36.3% with a variance of 28.5 km from the observed maximum rainfall position, while those of the default United States Geological Survey (USGS) dataset and Moderate Resolution Imaging Spectroradiometer (MODIS) dataset are 17.0%/32.8 km and 24.9%/49.0 km, respectively. The simulated total rainfall amount and occurrence time using the coupled refined datasets are the closest to the observed peak values. In addition, the HWSD soil data has improved the accuracy of the simulated precipitation amount, and the GLC2009 land cover data also did better in catching the early peak time.

Photochemical indicators of ozone sensitivity: application in the Pearl River Delta, China

Surface O3 production has a highly nonlinear relationship with its precursors. The spatial and temporal heterogeneity of O3-NOx-VOC-sensitivity regimes complicates the control-decision making. In this paper, the indicator method was used to establish the relationship between O3 sensitivity and assessment indicators. Six popular ratios indicating ozone-precursor sensitivity, HCHO/NOy, H2O2/ HNO3, O3/NOy, O3/NOz, O3/HNO3, and H2O2/NOz, were evaluated based on the distribution of NOx- and VOC-sensitive regimes. WRF-Chem was used to study a serious ozone episode in fall over the Pearl River Delta (PRD). It was found that the south-west of the PRD is characterized by a VOCsensitive regime, while its north-east is NOx-sensitive, with a sharp transition area between the two regimes. All indicators produced good representations of the elevated ozone hours in the episode on 6 November 2009, with H2O2/HNO3 being the best indicator. The threshold sensitivity levels for HCHO/NOy, H2O2/HNO3, O3/NOy, O3/NOz, O3/HNO3, and H2O2/NOz were estimated to be 0.41, 0.55, 10.2, 14.0, 19.1, and 0.38, respectively. Threshold intervals for the indicators H2O2/HNO3, O3/NOy, O3/NOz, O3/HNO3, and H2O2/NOz were able to identify more than 95% of VOC- and NOx-sensitive grids. The ozone episode on 16 November 16 2008 was used to independently verify the results, and it was found that only H2O2/HNO3 and H2O2/NOz were able to differentiate the ozone sensitivity regime well. Hence, these two ratios are suggested as the most appropriate indicators for identifying fall ozone sensitivity in the PRD. Since the species used for indicators have seasonal variation, the utility of those indicators for other seasons should be investigated in the future work.

Effect of different meteorological fields on the regional air quality modelling over Pearl River Delta, China

This study evaluates the performances of three Community Multiscale Air Quality (CMAQ) model v5.0 simulations that utilise meteorological input data from the 5th-generation Mesoscale Model (MM5), the Weather Research and Forecasting (WRF) model and WRF with Four-Dimensional Data Assimilation (WRF/FDDA). Three sets of CMAQ model simulations were performed for a high air pollution episode from October 9 to October 12, 2004 over the Pearl River Delta (PRD) region, which was caused by a high-pressure system. The observations at Guangzhou urban site (113.26°E, 23.13°N) were used to evaluate the results of meteorological models and air quality models. In all three experiments, the simulated pollutants were distributed mainly in the western part of PRD, but there was still a difference of horizontal distribution among them. The predicted wind fields, relative humidity and planetary boundary layer (PBL) height in meteorological simulations were the major factors contributing to this difference.

Impact of Land-Use Change on Atmospheric Environment Using Refined Land Surface Properties in the Pearl River Delta, China

We replaced the outdated land-use of the Weather Research and Forecasting-Chemistry (WRF-Chem) model with a refined dataset, the Global Land Cover 2009 (GLC2009) dataset, to investigate the impact of land-use change on the regional atmospheric environment in the Pearl River Delta (PRD) region. Simulations of two months in 2014 (January and July) showed that land-use change increased the monthly averaged 2 m temperature by 0.24°C and 0.27°C in January and July, respectively. The relative humidity decreased by 2.02% and 2.23% in January and July, respectively. Due to the increase in ground roughness, the monthly averaged wind speed in January and July decreased by 0.19 m/s and 0.16 m/s. The planetary boundary layer height increased throughout the day and with larger relative increase during the nighttime. These subtle changes caused by land-use resulted in discernable changes in pollutant concentrations. Monthly averaged surface O3 concentration increased by 0.93 µg/m3 and 1.61 µg/m3 in January and July, while PM2.5 concentration decreased by 1.58 µg/m3 and 3.76 µg/m3, and the changes in pollutant concentrations were more noticeable during the nighttime. Overall, the impacts of land-use change on the atmospheric environment are obvious throughout the PRD region, especially in the urbanized areas.