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Recently, the high PCDD/F emissions observed in the coastal provinces of eastern China have raised global concerns over their adverse effects on human health. To address the effects of the long-range transport of persistent organic pollutants, the observations of atmospheric PCDD/F pollution were conducted across Southeast Asian in this study. Atmospheric PCDD/F levels were evaluated at two background stations (Sites A and B) in Taiwan, three remote islands (Sites C, D and E) around Taiwan and at Dongsha Island (Site F) in South China Sea at various times. Significantly lower atmospheric PCDD/F concentrations (1.24–7.75 fg I-TEQ m−3) and PCDD/F contents (3.45–49.1 pg I-TEQ/g-TSP) in total suspended particles (TSPs) were measured during the summer season. Based on a 72-h backward trajectory analysis conducted for the sampling sites used in this study, the air mass containing theses low levels had originated from the Pacific Ocean and South China Sea during the summer. The highest PCDD/F concentrations (10.2–65.2 fg I-TEQ m−3) and PCDD/F contents (132–620 pg I-TEQ/g-TSP) in ambient air were measured in northern Taiwan (Site A) and at two islands (Site C and Site E) close to mainland China during the northeast monsoon periods. In the meantime, the PCDF compounds in ambient air also increased from 52–54% to 65–75% at those sampling sites. Based on these measurements and corresponding trajectory analysis, we conclude that the significant increase in atmospheric PCDD/Fs measured during the northeast monsoon period in this study was attributable to the long-range transport of emissions from the coastal regions of mainland China. [ABSTRACT FROM AUTHOR]

Abstract: Surface ozone (O3) and carbon monoxide (CO) mixing ratios were measured at Mei-Feng (24.05 °N, 120.10 °E, 2269 m above sea level) remote mountain site between March 2009 and September 2010 to investigate the impact of regional pollution on O3 and CO. The results showed that the maximum values of both O3 and CO were found in the springtime. Backward trajectory analysis, combined with MODIS fire spots suggested that the enhanced O3 and CO in springtime could be attributed to biomass burning (BB) activities over Southeast (SE) Asia. Thirteen BB events were identified by backward trajectory analysis, MODIS fires, NCEP weather data sets and CO concentrations. Good correlation between O3 and CO was found during the BB plumes. Using the linear regression, the slope (ΔO3/ΔCO) was calculated to be 0.18 ± 0.08 (mean ± 1σ). This value was in agreement with that of 0.2 observed over the west Pacific region during the TRACE-P campaign, but was higher than those (0.11–0.14) of Canadian and Siberian fires. Moreover, significant enhanced O3 productivity was also found in aged BB plumes and that mixed with urban emissions from SE coastal China. To assess the net influence of SE Asian BB, the air masses from SE Asia and SE China were divided in two groups: those that passed over the fire regions (PF) and those that did not (NP). The result showed that the maximum differences between PF and NP were estimated in March with 8 ppb for O3 and 45 ppb for CO, respectively, accounting for 23% of both CO and O3 levels at Mei-Feng. Although uncertainties existed in the estimations, the significant discrepancies of O3 and CO in the two air groups suggested the air pollutants emitted by SE Asian BB could be transported and influence the air quality over subtropical Taiwan in springtime. [Copyright &y& Elsevier]

Abstract: The impacts of long-range transport of Asian dust and anthropogenic air pollutants to Taiwan are strongly associated with the atmospheric conditions and paths of transport. In this study, we identified 16 significant dust events (daily mean mass concentration ≥ 120 μg m−3) to Taiwan from 2002 to 2008. To investigate transport characteristics associated with long-range transport of Asian dust and anthropogenic air pollutants to Taiwan, significant dust events were further classified into dry (12 cases) and wet (4 cases) types according to atmospheric conditions. We found that the major transport paths for the dry type (DT) dust cases passed through anthropogenic source areas in the low boundary while the major paths for the wet type (WT) dust cases passed over the ocean. After mineral dust, which occupied around 32% of total PM10 mass concentration, anthropogenic ionic pollutants was the second major contributor and occupied 19–22% at three sampling stations in Taiwan for DT cases. In the fine particle, the anthropogenic ionic pollutants contributed from 29 to 36% to PM2.5, making it the major contributor. The two most significant cases, one from the DT and one from the WT cases, were selected to study transport mechanisms with the NAQPMS air quality model. Simulation results also suggest that transport paths and boundary atmospheric conditions play important roles in aerosol compositions. [Copyright &y& Elsevier]

Abstract: Kaohsiung City and the suburban region of southwestern Taiwan have suffered from severe air pollution since becoming the largest center of heavy industry in Taiwan. The complex process of ozone (O3) formation and its precursor compounds (the volatile organic compounds (VOCs) and nitrogen oxide (NO x ) emissions), accompanied by meteorological conditions, make controlling ozone difficult. Using a decision tree is especially appropriate for analyzing time series data that contain ozone levels and meteorological and explanatory variables for ozone formation. Results show that dominant variables such as temperature, wind speed, VOCs, and NO x can play vital roles in describing ozone variations among observations. That temperature and wind speed are highly correlated with ozone levels indicates that these meteorological conditions largely affect ozone variability. The results also demonstrate that spatial heterogeneity of ozone patterns are in coastal and inland areas caused by sea-land breeze and pollutant sources during high ozone episodes over southwestern Taiwan. This study used a decision tree to obtain quantitative insight into spatial distributions of precursor compound emissions and effects of meteorological conditions on ozone levels that are useful for refining monitoring plans and developing management strategies. [Copyright &y& Elsevier]

Abstract: To quantify the possible sources of the high ambient ozone concentration in the low troposphere over Taiwan, ozone sounding data from a two-year intensive field measurement program conducted in April and early May of 2004 and 2005 in northern Taiwan has been examined. We found that the vertical ozone distributions and occurrence of enhanced ozone in the lower troposphere (below 6 km) mainly resulted from (1)Type NE: the long-range transport of ozone controlled by the prevailing northeasterly winds below 2 km, (2)Type LO: the local photochemical ozone production process, and (3)Type SW: the strong southwest/westerly winds aloft (2–6 km). In the boundary layer (BL), where Asian continental outflow prevails, the average profile for type NE is characterized by a peak ozone concentration of nearly 65 ppb at about 1500 m altitude. For type LO, high ozone concentration with an average ozone concentration greater than 80 ppb was also found in the BL in the case of stagnant atmospheric and sunny weather conditions dominated. For type SW, significant ozone enhancement with average ozone concentration of 70–85 ppb was found at around 4 km altitude. It is about 10 ppb greater than that of the types NE and LO at the same troposphere layer owing to the contribution of the biomass burning over Indochina. Due to Taiwan''s unique geographic location, the complex interaction of these ozone features in the BL and aloft, especially features associated with northeasterly and south/southwesterly winds, have resulted in complex characteristics of ozone distributions in the lower troposphere over northern Taiwan. [Copyright &y& Elsevier]

The impact of the urban heat island (UHI) effect on environmental and regional climate has been receiving wide attention in recent decades. Taiwan, especially Taipei (located in northern Taiwan), is experiencing a significant UHI effect due to its high population density and the uniqueness of the geographic structure. In order to evaluate the impacts of urbanization and UHI effect over northern Taiwan, a next generation mesoscale model, Weather Research and Forecasting (WRF) model coupled with the Noah land surface model and Urban Canopy model (UCM), was used to study this issue. By using the WRF–Noah–UCM model, it has significantly improved our simulation results for the prediction of the UHI effect, boundary layer development, and land sea breeze. Observations of weather stations and Lidar showed that the near surface air temperature was nearly 34–35°C and the boundary layer height was nearly 1500m around noon in Taipei on 17 June 2006. Around midnight, the air temperature ranged from 26 to 28°C. Our model can predict well for boundary layer development during the daytime and the UHI effect in northern Taiwan. Sensitivity tests indicate that the anthropogenic heat (AH) plays an important role for the boundary layer development and UHI intensity in the Taipei area, especially during nighttime and early morning. When we increase AH by 100Wm−2 in the model, the average surface temperature could increase nearly 0.3°C in Taipei. Furthermore, we found the UHI effect also has a significant impact on land sea circulation. It could enhance the sea breeze in the daytime and weaken the land breeze during the nighttime and hence had a significant impact on the air pollution diffusion in northern Taiwan. [Copyright &y& Elsevier]

A highly developed industry and a large population density have turned the western plain of Taiwan into a mega-suburb with many cities and small towns and countless factories, and roads. As a result, the western plain is experiencing a regional heat-island effect. The MM5 mesoscale model was conducted in order to study and evaluate the impacts of the heat-island effect on regional weather, including thunderstorms, over Taiwan. According to land use data provided by the US Geological Survey (USGS), we assumed three different urban sizes in the simulation study to theoretically evaluate the impact of urbanization on the precipitation. Along with urban size increase in central Taiwan, more pronounced effects of meteorological parameters were shown in the sensitivity experiment with urban cases. For the urban case (case SA, with urban size 15×15km2), sensible heat flux is nearly 500Wm−2 around noon-time. It is about a factor of 3 more than the non-urban case (case CT) over the western plain. The surface air temperature in case SA increased by nearly 3°C and humidity decreased with nearly 10% more than case CT. Along with the urban size increases in central Taiwan, the effects are the surrounding areas and were more pronounced not only the precipitation over downwind areas. Apparently, the unique and complex topographic features in Taiwan, including the lifting effect of the mountain bordering the western plain, are also play important roles for precipitation formation. Numerical study suggests that the heat-island effect over the western plain could perturb thermal and dynamic processes and hence affect the location of thunderstorms and precipitation over Taiwan''s western plain. [Copyright &y& Elsevier]

Elevated ozone concentration is one of the current major environmental concerns in Taiwan. The spatial distribution and seasonal variations of ground level ozone over Taiwan are investigated by using air quality network stations of Taiwan Environmental Protection Administration (TEPA). Data shows that high ozone episodes frequently occur over southwest Taiwan during autumn. In this season, shallow northeasterly winds prevail after frontal passage and are diverted by the Central Mountain Range (CMR) because of its mean altitude of about 2. 5km. The windward side in northern Taiwan is usually associated with cloudy days, whereas sunny days with weak wind speeds usually occur on the lee side of the CMR over southwest Taiwan due to topographical blocking. Numerical results indicate that anthropogenic emissions from the north of Kaohsiung could contribute as much as 41% of ozone for the Kaohsiung metropolitan area and 24% for the inland rural Pingtung area during the northerly flow. It is concluded that the contribution of the emissions from the north of Kaohsiung is significant and cannot be ignored. The northerly air masses, which flows over the western plain during daytime, picks up ozone and its precursors which are transported to southwestern Taiwan. After a sea breeze develops, strong onshore flow transports significant amounts of ozone and precursors to the inland rural areas resulting in the high ozone episodes that frequently occur over southwestern Taiwan during the autumn season. [Copyright &y& Elsevier]

Abstract: The impact of long-range transport on the air quality of Taiwan was assessed by using measurements at stations of the air quality monitoring network of the Taiwan Environment Protection Administration over the winter monsoon periods of 2000 and 2001. The primary long-range transport process can be clearly identified to be the prevailing northeasterly following the cold front of winter monsoon that originates in the Asian continent. Based on pollutants concentration differences among different meteorological conditions, we estimate that the long-range transport of particulate pollutants contributes to about 30μgm−3 to the PM10 concentrations in northern and eastern Taiwan. A smaller contribution is estimated for the western plain of Taiwan. Contributions of the long-range transport to CO and SO2 are about 230 and 0.5ppb, respectively. The identified, dust events have the highest average inflow concentration (about 71±34μgm−3) of PM10. The dust impacts on PM10 have been estimated to be nearly 100% at windward background stations along the north and northeast coast. In the northern cities of Taiwan, such as Taipei and Hsinchu, the impacts decrease to around 60–80% as local emission increase. Due to geographic blocking, a smaller impact is estimated for the western plain of Taiwan. However, the identified frontal pollution cases have significant impact on CO and SO2, which is more evident than the impact of dust events. In general, impacts of long-range transport on air pollutants at coastal stations are greater than those in urban areas. [Copyright &y& Elsevier]

Abstract: Intensive measurements of aerosol (PM10) and associated water-soluble ionic and carbonaceous species were conducted in Guangzhou, a mega city of China, during summer 2006. Elevated levels of most chemical species were observed especially at nighttime during two episodes, characterized by dramatic build-up of the biomass burning tracers levoglucosan and non-sea-salt potassium, when the prevailing wind direction had changed due to two approaching tropical cyclones. High-resolution air mass back trajectories based on the MM5 model revealed that air masses with high concentrations of levoglucosan (43–473 ng m−3) and non-sea-salt potassium (0.83–3.2 μg m−3) had passed over rural regions of the Pearl River Delta and Guangdong Province, where agricultural activities and field burning of crop residues are common practices. The relative contributions of biomass burning smoke to organic carbon in PM10 were estimated from levoglucosan data to be on average 7.0 and 14% at daytime and nighttime, respectively, with maxima of 9.7 and 32% during the episodic transport events, indicating that biomass and biofuel burning activities in the rural parts of the Pearl River Delta and neighboring regions could have a significant impact on ambient urban aerosol levels. [Copyright &y& Elsevier]

Abstract: In recent years, the high levels of surface ozone have become a major air pollutant in Taiwan. Over the western plain of Taiwan, where most of the 23 million inhabitants live, the concentration of ozone increased substantially during the last ten years (1994–2003). This increase is puzzling as the emissions of ozone precursors, oxides of nitrogen (NO x ) and volatile organic compounds (VOCs) or non-methane hydrocarbon (NMHC) decreased significantly in the same period. An in-depth analysis focusing on “total oxidant” (estimated by O3+NO2) showed that its concentration remained essentially constant in Taipei, Taiwan, during that same ten year time period. Given that the regional tropospheric ozone is increasing, the constant oxidant level suggests that the oxidant production from photochemical reactions in Taipei should have been reduced to some extent, due to the reduction in emissions of ozone precursors. Consequently, the increasing trend in ozone was a result of the reduced titration by NO. These results are important to the formulation of ozone control strategies, especially for newly developed countries like Taiwan. [Copyright &y& Elsevier]

Abstract: Ambient air samples were collected at 13 air quality monitoring stations in Kaohsiung city, Kaohsiung county, and Pingtung county (KKP) to investigate the composition and spatial distribution of C2–C10 non-methane hydrocarbons (NMHCs) in southern Taiwan. Ozone formation potentials (OFPs) of NMHCs were estimated using maximum incremental reactivity (MIR) and k OH method (reactivity of NMHC with OH radical) to assess the relative effects of hydrocarbons on ozone formation. The measurements showed that mixing ratios of toluene, ethene, ethyne, ethane, isopantane and propane were the highest among all measured species at most of the sampling sites. Nevertheless, considering both the photochemical reactivities and mixing ratios of all the measured species, toluene, xylene, ethene and propene were calculated to have the highest OFPs and reactivities. The OFPs and reactivities assessed by the MIR and k OH methods for the four compounds accounted for 54.5% and 39.3% of all the measured species. Larger benefit margin of ozone abatement may be obtained by reducing emissions of a group of key species with high OFPs. 2,2-dimethylbutane (22DMC4) was used as an indicator of traffic emissions to distinguish traffic from non-traffic contributions of key species in Kaohsiung metropolitan area. It revealed that the contribution of non-traffic source was significant for toluene, whereas xylene was found to be primarily from the traffic source in Kaohsiung metropolitan area during the sampling periods. [Copyright &y& Elsevier]

Abstract: We identify the directionality of sources contributing to observed pollutant concentrations at a rural site through the use of the analysis methods of Conditional Probability Function (CPF) and the Source Direction Probability (SDP). Input data consists of hourly averaged PM2.5 mass, Organic Mass (OM) from Organic Carbon (OC), optical Elemental Carbon (optical EC), SO2, CO, NOy, O3 concentrations and metrological data from Pinnacle State Park site in rural New York State for the period of Dec 2004 to Dec 2008. These measured pollutants are coupled with on-site wind data to identify the directionality of the sources; which are then compared to known stationary source locations from the EPA Air Data web site. Although the CPF plot of the O3 showed no distinct directionality source area, the Pinnacle State Park site was frequently impacted by plumes of relatively high PM2.5 mass, SO2, CO, NOy, optical EC and OM concentrations. Further analysis of the enhanced pollution occurrence frequency from the eastern sector revealed two peaks in the time-of-day distribution of elevated CO, NOy, and optical EC, which provides additional information on the sources. This contrasts with the enhanced pollution occurrence frequency from the south for CO, OM, and optical EC, which shows a single morning peak in its time-of-day distribution and indicates a somewhat more distant, but common source for these carbon-containing pollutants. PM2.5 mass corresponds to the source areas related to emission facilities listed in the EPA Emissions Inventory, which is further confirmed by correlation and analysis of aerosol optical depth (AOD) data from Moderate-resolution Imaging Spectrometer (MODIS) on board Terra and Aqua satellites. We present evidence that most of the high pollution episodes likely arise from emission sources located several hundred kilometers from the site, indicating mid-long range transport of pollutants to this location. [Copyright &y& Elsevier]

An observation-based method (OBM) is developed to evaluate the ozone (O3) production efficiency (O3 molecules produced per NO x molecule consumed) and O3 production rate (P(O3)) during a field campaign in southern Taiwan. The method can also provide an estimate of the concentration of OH. A key step in the method is to use observed concentrations of two aromatic hydrocarbons, namely ethylbenzene and m,p-xylene, to estimate the degree of photochemical processing and amounts of photochemically consumed NO x and NMHCs by OH. In addition, total oxidant (O3+NO2) instead of O3 itself turns out to be very useful for representing ozone production in the OBM approach. The average O3 production efficiency during the field campaign in Fall (2003) is found to be about 10.2±3.9. The relationship of P(O3) with NO x is examined and compared with a one-dimensional (1D) photochemical model. Values of P(O3) derived from the OBM are slightly lower than those calculated in the 1D model. However, OH concentrations estimated by the OBM are about a factor of 2 lower than the 1D model. Fresh emissions, which affect the degree of photochemical processing appear to be a major cause of the underestimate. We have developed a three-dimensional (3D) OBM O3 production diagram that resembles the EKMA ozone isopleth diagram to study the relationship of the total oxidant versus O3 precursors. The 3D OBM O3 production diagram suggests that reducing emissions of NMHCs are more effective in controlling O3 than reducing NO x . However, significant uncertainties remain in the OBM, and considerable more work is required to minimize these uncertainties before a definitive control strategy can be reached. The observation-based approach provides a good alternative to measuring peroxy radicals for evaluating the production of O3 and formulating O3 control strategy in urban and suburban environments. [Copyright &y& Elsevier]