Taiwan Air Quality Research Articles

Offset Ratio Assessment for Volatile Organic Compounds in Cap and Trade Zone

Kaohsiung and Pintung are the first regions were set into action of total quantity control zones for air quality in Taiwan. Cap and trade programs have built for the particle matters (PM10), sulfur oxides (SOx), nitrogen oxides (NOx) and Volatile Organic Compounds (VOCs) in 2010. The offset ratio was designed as 1.0 or 1.2 various on the offset sources. The fixed offset ratio setting is suitable for PM10, SOx, and NOx since their characters are unitary. However, VOCs include a variety of chemicals, some of which may have short- or long-term adverse health effects. Even the same pollutant trading amount cannot guarantee the same health risk or environmental impacts. It would induced the highly uncertainty of air quality for the fixed offset ratio system. This study therefore tried to create a new methodology based on the pollutant impact strength of health and environment for determining the offset ratio of VOCs. An equation for calculating the offset ratio of VOCs was proposed and evaluated by case study. The elasticity of weighting determination was remained to the decision makers for confronting the various environmental improving targets.

Airborne Microorganisms at a Senior High School in Chang-Hua County, Taiwan

Bioaerosols are a type of suspended sediments that contribute to poor air quality in Taiwan. Bioaerosols include allergens such as fungi, bacteria, actinomycetes, arthropods, and protozoa, as well as microbial products such as mycotoxins, endotoxins and glucans. When allergens and microbial products are suspended in the air, local air quality is adversely influenced. In addition, when the particle size is small enough to pass through the human respiratory tract, the health of the local population is also threatened. The classroom is where students spend a large portion of weekday time and thus could play an important role in student's exposure to potential threatening bioaerosols. The purpose of this study was to understand the airborne bacteria and fungi concentrations at a sampling classroom (with the windows opened and closed) from a senior high school in Chang-Hua County, Taiwan. The results indicate that the total average bacterial concentrations were 2.2 × 103, 1.7 × 103, 7.8 × 102, 1.2 × 103, 7.4 × 102 and 7.6 × 102 cfu/m3 using tryptic soy agar (TSA)-medium incubated for 48 hr under various sampling conditions in the morning, afternoon, and evening with windows closed and opened, respectively (i.e., morning with windows closed [MC], afternoon with windows closed [AC], evening with windows closed [EC], morning with windows opened [MO], afternoon with windows opened [AO], and evening with windows opened [EO]) at the sampling classroom. Moreover, the total average fungi concentrations were 1.1×103, 7.3×102, 6.3×102, 7.4×102, 5.8×102, and 6.2×102 cfu/m3 using malt extract agar (MEA) medium incubated for 96 hr under the same various sampling conditions (MC, AC, EC, MO, AO, and EO). The total average bacterial and fungi concentrations were higher with windows closed than with windows opened during any sampling period. Ventilation is the possible reason for the above finding. The highest average bacterial or fungi concentrations was found in the particle size of 0.53 mm (average bioaerosol size was in the range of 2.1–3.3 μm) for any sampling condition. These findings may be relevant in a forensic investigation related to a potential bioattack, since it provides baseline information of bioaerosols composition (e.g., before an attack is initiated) within the tested environment.

The Impact of Yellow Dusts From China on Air Quality in Northern Taiwan From 1994 to 2008

PP-29-035 Background/Aims: Air quality in Taiwan has been improved in recent years, causing significant changes in the yellow dusts from north-west China affecting Taiwan. The objective of this study is to recognize the effect of yellow dust on Taiwan originating from China on a daily basis. Methods: Between 1994 and 2008, the data are derived from hourly particulate matter (PM10) and CO value taken from the monitoring stations located in the city center, northern and eastern coast, and national park. We determine that a day is affected by dust when PM10 concentration increases from both northern and eastern coast, and the National Park monitoring stations simultaneously, and at the same time, the daily average concentration of PM10 from the city center monitoring station records values >125 μg/m3. We also distinguish the Asian dust events by measuring decreasing CO levels during the dust period, and increasing CO levels during periods of locally accumulating pollution. Results: It is estimated that 53 dust events were influenced by yellow dust from China during 1994 to 2008, with the most occurrences during 2000 to 2007 showing an increasing trend, especially during 2000 where occurrences went up to 9. The most frequent times occurred in the months of March and April, totaling at 46%. On average, the concentration of PM10 in dust impact day is 4 times higher than its non-dust impact day. In addition, CO is not accumulated in dust impact day. Conclusion: Taiwan is largely affected by the dust storms from China, even though it is away from the originate area of dust. Increasing PM concentrations in the ambient air causes human health hazards such as respiratory tract and cardiovascular disease. We should enforce our authority to concern this issue and do better in forecast.

Increased Risk of Acute and Chronic Conjunctivitis Associated With Ambient Air Quality in Taiwan

Increased Risk of Acute and Chronic Conjunctivitis Associated With Ambient Air Quality in Taiwan

Fugitive Dust Emission Source Profiles and Assessment of Selected Control Strategies for Particulate Matter at Gravel Processing Sites in Taiwan

Particles emitted from gravel processing sites are one contributor to worsening air quality in Taiwan. Major pollution sources at gravel processing sites include gravel and sand piles, unpaved roads, material crushers, and bare ground. This study analyzed fugitive dust emission characteristics at each pollution source using several types of particle samplers, including total suspended particulates (TSP), suspended particulate (PM10), fine suspended particulate (PM2.5), particulate sizer, and dust-fall collectors. Furthermore, silt content and moisture in the gravel were measured to develop particulate emission factors. The results showed that TSP (<100 µm) concentrations at the boundary of gravel sites ranged from 280 to 1290 µg/m3, which clearly exceeds the Taiwan hourly air quality standard of 500 µg/m3. Moreover, PM10 concentrations, ranging from 135 to 550 µg/m3, were also above the daily air quality standard of 125 µg/m3 and approximately 1.2 and 1.5 times the PM2.5 concentrations, ranging from 105 to 470 µg/m3. The size distribution analysis reveals that mass mean diameter and geometric standard deviation ranged from 3.2 to 5.7 µm and from 2.82 to 5.51, respectively. In this study, spraying surfactant was the most effective control strategy to abate windblown dust from unpaved roads, having a control efficiency of approximately 93%, which is significantly higher than using paved road strategies with a control efficiency of approximately 45%. For paved roads, wet suppression provided the best dust control efficiencies ranging from 50 to 83%. Re-vegetation of disturbed ground had dust control efficiencies ranging from 48 to 64%.

Asian dust and pollution transport—A comprehensive observation in the downwind Taiwan in 2006

This study analyzed the air pollution episode which affected Taiwan on March 19 and 20, 2006, an event confirmed to have been caused by Asian dust (AD). During this AD event, the maximum hourly values of PM 2.5 and PM 2.5–10 particles at 136 and 218 µg m − 3 , respectively, were recorded at the Taipei aerosol supersite (TAS) located in northern Taiwan. Moreover, of Taiwan's 74 air quality monitoring stations, 65 (on March 19) and 29 stations (March 20) recorded daily average concentrations of PM 10 which exceeded Taiwan's air quality standard of 125 µg m − 3 . This AD event not only greatly increased the PM 2.5 and PM 2.5–10 concentrations, but the gaseous pollutants transported by the northeast monsoon were predicted to adversely affect Taiwan as well. In addition to ground measurements, an aerosol layer was detected in Taipei, the thickness of which was verified to be about 800 m through the light detection and ranging (LIDAR) method. During the AD-affected period (defined as the situation where the concentration of PM 2.5–10 maintains a high value), the black carbon (BC) fraction of PM 2.5 was reduced from 15.7 to 5.6%; sulfate fraction of PM 2.5 increased from 7.1 to 19.8%; and the nitrate fraction of PM 2.5 was reduced slightly from 10.3 to 8.1% at the TAS site. Moreover, the particles' number size spectra showed a decrease in the amount of particles with a diameter of less than 200 nm, indicating that the rise of the concentration of PM 2.5 increased along with the increase of PM 2.5 particles with diameters larger than 200 nm. This study demonstrates that anthropogenic pollutants from the Asian mainland including nitrates, sulfates, BC, gaseous pollutants (CO, SO 2, and O 3), and other fractions of fine particles, would influence the downwind regions as the AD is transported.

Bioaerosols as contributors to poor air quality in Taichung City, Taiwan

Bioaerosols are a type of suspended sediments that contribute to poor air quality in Taiwan. Bioaerosols include allergens such as: fungi, bacteria, actinomycetes, arthropods and protozoa, as well as microbial products such as mycotoxins, endotoxins and glucans. When allergens and microbial products are suspended in the air, local air quality will be influenced adversely. In addition, when the particle size is small enough to pass through the respiratory tract entering the human body, the health of the local population is also threatened. Therefore, the purpose of this study is to attempt to understand the concentration and types of bacteria and the bacteria numbers for various particle size ranges during a study period of June 2005 to February 2006 in Taichung City, Central Taiwan. The results indicate that the total average bacterial concentration by using NA medium incubated for 48 h were 8.0 x 10(2), 1.4 x 10(3), 2.4 x 10(3) and 1.3 x 10(3), 1.9 x 10(3), 3.5 x 10(3) cfu/m(3) for CMES, TRIPS and RFS sampling sites during the daytime and nighttime period of June 2005 to February 2006. Moreover, the total average bacterial concentration by using R(2)A medium incubated for 48 h were 8.5 x 10(2), 1.5 x 10(3), 2.2 x 10(3) and 1.2 x 10(3), 1.7 x 10(3), 2.5 x 10(3) cfu/m(3) for CMES, TRIPS and RFS sampling sites the daytime and nighttime during the same sampling period. The total average bacteria concentration was the same in either NA or R(2)A medium for the same sampling times or sites. The total average bacterial concentration was higher in daytime period than that of nighttime period for CMES, TRIPS and RFS sampling sites. The high average bacterial concentration was found in the particle size range of 0.53-0.71 mm (average bioaerosol size was in the range of 2.1-4.7 microm) for each sampling site. Also, 20 kinds of bacteria exceeded levels for each sampling site and were classified as according to shape: rod, coccus and filamentous.

Retrospective assessment of air quality management practices in Taiwan

In 1995, Taiwan's Environmental Protection Administration (EPA/TW) instituted a policy of levying emission taxes on polluters in order to combat the rampant national issue of pollution. Since that time, pollution control strategies, tightening exhaust emission standards for industry, improvements in fuel quality, and new stricter vehicle emission standards, etc., have been implemented. This study evaluates the effectiveness of these measures and examines the improvement of Taiwan's air quality. In this paper, we conduct a detailed analysis of change in the concentrations of pollutants (SO 2, NO x and particulate matter [PM]) between two three-year periods (from 1996 to1998 and from 2000 to 2002). The pollution levels were generally lower in the latter period. Concentrations at 14 EPA/TW stations in central Taiwan were simulated and source apportionment analyses in three of Central Taiwan's largest cities were conducted using a trajectory transfer-coefficient air quality model. Correlation coefficients ( r) between simulations and observations for the monthly means of the concentrations of SO 2, NO x , PM 2.5 and PM 10 during the study periods at the 14 stations are 0.56, 0.63, 0.70 and 0.31, respectively. The sulfur control policy greatly reduced SO 2 concentration island-wide, a stringent emission standard put into place for gasoline vehicles reduced NO x concentration along highways, and an emissions tax placed on construction sites, as well as a regular program for road-dust sweeping, reduced primary particulate matter. Among all of the pollution abatement policies implemented, the most effective method for reducing PM 2.5 concentrations in the three largest cities involved the reduction of fine ammonium sulfate aerosols from point sources (56–63% of net PM 2.5 reduction). The next largest reduction was attributed to a diminishment in primary PM 2.5 emanating from point sources (27–56% of net PM 2.5 reduction). Secondary particulate matter, especially sulfate, was reduced from distances up to 150 km leeward of major pollution point sources such as Taichung Power Plant.

Southeastward transport of Asian dust: Source, transport and its contributions to Taiwan

Atmospheric Aluminum measured in northern Taiwan from 2003 to 2006 is used as a dust tracer, from which dust concentrations are derived, and major Asian dust events are determined. The source locations for the major dust events are traced back and identified, and the processes leading to the southeastward transport of Asian dust is investigated. The derived dust concentrations are compared to the local PM 10 (particle with size less than 10 μm) concentrations, and the impacts of Asian dust on the air quality of Taiwan are quantified. According to the backward trajectory and dust observation analyses, most of the southeastward transport of major Asian dust events originate from Mongolia and Inner Mongolia in northern China, and only one out of 16 events is generated from western China. Modeling studies and weather analyses of dust events suggest that the southeastward transport of Asian dust is usually generated behind a surface front and transported downwind behind the associated upper level trough. The associated upper level trough is usually deep, in which the northwesterly wind behind the trough favors the southeastward transport of dust to lower latitudes. Dust transported to Taipei generally occur during periods of large-scale subsidence. Asian dust contributes about 15 μg m −3 of aerosol particles to northern Taiwan during winter monsoon, which accounts for about 24–30% of the PM 10 concentrations to the northern Taiwan. The contributions of Asian dust are raised pronouncedly to about 60–70% during major dust events. The impacts of Asian dust on Taiwan's air quality are most substantial in December. The Asian dust impacts decrease in other months, but still remain at around 30% in the late winter to early spring.

Climate variability of cold surge and its impact on the air quality of Taiwan

Climate change has been receiving wide attention in the last few decades. In order to quantify the climate variability of extreme weather events and their possible impacts on weather parameters and air quality, cold surge events in the past 45 years and the difference in characteristics of air pollutants before and after frontal passage has been examined after December 1993 in Taiwan. The potential impact of climate change on air pollutant concentration and its health implication were presented and discussed. In the past 45 years, the cold surge days (about 18.7 days, or 0.42 day/year) decreased significantly and the average lowest daily temperature for winter in northern Taiwan increased nearly 3°C (0.067°C/year). Based on the definition of cold surge in Taiwan and excluding the stagnation frontal passage, 21 cold surge frontal passage (CSFP) cases and 89 common frontal passage (CFP) events in winter (December–February) were identified in the past 12 years (1993–2005). We take the frontal passage day as the baseline and the differences in air pollutant concentrations and weather-related parameters between the two days before and after the frontal passage days were examined for each case. The averages of the above-mentioned differences during CSFP were compared to the corresponding differences during CFP. During CSFP, the air temperatures after the frontal passage were nearly 4–6°C lower than before the passage at both the background windward stations and urban stations. The average wind speed was about 4–5 m/s higher at the windward stations and less than 2 m/s higher in the major urban areas in Taiwan. During CFP, there was a 2°C increase in temperature but 1 m/s decrease in wind speeds on the day after frontal passage. Because of these meteorological differences, the concentration change of air pollutants during CSFP is significantly greater than that during CFP, especially for PM10 concentration. The difference of PM10 concentration during CSFP can be as large as 20–40 μg/m3 while that during CFP is only about 10 μg/m3. The differences in the other air pollutants such as CO, SO2, and O3 during CSFP are greater than those during CFP, but the difference is insignificant. Under the warming trend, less frequent CSFP’s are expected; the impacts on deterioration of air quality and human health are noteworthy.

Particle size characteristics of levoglucosan in ambient aerosols from rice straw burning

Agricultural residue burning in Asia is an important source of atmospheric aerosol particles. This study investigates the impact of post-harvest burning of rice fields on the air quality in Taiwan, a subtropical island in East Asia. Size-resolved measurements of the anhydrosugar levoglucosan (biomass burning tracer derived from the thermal breakdown of cellulose) were conducted before, during and after an episode of intensive rice straw burning at a rural and suburban site. While substantially enhanced levoglucosan concentrations were observed during the active rice straw burning episode (up to 1400 ng m −3), fairly high values of the smoke tracer were measured throughout the entire study period. Moreover, unusually high levoglucosan levels were present in aerosol particles with aerodynamic diameters larger than 10 μm (PM >10), possibly influenced by the ambient atmospheric conditions, such as high relative humidity, in addition to unique properties of rice straw smoke and the specific burning practices of rice fields.

Modeling approach for emission reduction of O 3 precursors in Southern Taiwan

Although the upgraded criteria air quality standards (O 3, SO x , NO x and PM 10) and more stringent stack emission standards have significantly improved the overall air quality in Taiwan, the southern region of Taiwan frequently exhibits undesirable PSI (pollutant standard index), due to intensive industrial outputs and heavy traffic volume. For example, the percent of the time with PSI >100 in Taiwan has been reduced from 7% in 1994 to 4.3% in 2005, but there is still about 6.5% of the time with PSI > 100 in the southern region in 2005, of which 77% is due to O 3 contribution. The main goal of the present study is to develop a control strategy for reduction of NO x and NMHCs for reducing O 3 levels. The maximum 1-h O 3 isopleth profiles for southern Taiwan were first established based on 40 cases of different emission quantities of NO x and NMHCs using Taiwan Air Quality Model (TAQM) with four-level nested domains. The emission rates of O 3 precursors from other regions are assumed to be constant and exert the same effect on the air quality under different weather conditions in southern Taiwan. To meet the air quality goals, the allowable capacity for NO x and NMHCs in this region was determined by the following two methods: (a) linear and (b) cumulated frequency. The allowable capacity of NO x and NMHC to meet a certain goal can be easily demonstrated by plotting arbitrary reduction lines in the O 3 isopleth profiles. To meet the goal in the year 2011 (or O 3 151 ppb from the cumulated frequency method), for example, the emission reduction NO x /NMHC for 1:4 case amounts to 75 and 300 ton d −1, respectively, for NO x and NMHC; the corresponding emission rates are 290 and 430 ton d −1 (or 21 and 41% reduction, respectively). Clearly, there are many possibilities for achieving the desirable goal by manipulating reduction quantities in both NO x and NMHC.

The Study of Ambient Air Bioaerosols During Summer Daytime and Nighttime Periods in Taichung, Central Taiwan

Suspended particles, of which bioaerosols are one type, constitute one of the main reasons for poor air quality in Taiwan. Bioaerosols include allergens such as fungi, bacteria, actinomycetes, arthropods, and protozoa, as well as microbial products such as mycotoxins, endotoxins, and glucans. When allergens and microbial products are suspended in the air, local air quality will be influenced severely. When the particle size is small enough to pass through the respiratory tract entering the human body, the health of the local population is threatened. Therefore, the purpose of this study was to understand the concentration and types of bacteria during the summer period at four sampling sites in Taichung, central Taiwan. The total average bacterial concentrations at 48-h incubation time during the summer daytime period were 8.1 × 102, 1.9 × 103, 3.7 × 10 3, and 1.1 × 103 cfu/m3 and nighttime period were 1.1 × 103, 2.6 × 103, 3.2 × 103, and 1.9 × 103 cfu/m3 from June 30 to August 1, 2005. The average bacterial concentration increased as the incubated time increased for each particle size range. The high average bacterial concentration was found in the particle size 0.34–0.71 mm (average bioaerosol size was in the range of 1.1–4.7 μm) for each sampling site. There were more than 20 types of bacteria at each sampling site and the bacteria shapes were rod, coccus, and filamentous.

Identification of Regional Air Pollution Characteristic and the Correlation with Public Health in Taiwan

This study aims to classify regions with different air pollution characteristics into groups in Taiwan, and further to evaluate and compare the air quality of various groups. A selected multivariate analysis technique, cluster analysis, is applied to the pollution monitoring dataset which including PM10, SO2, NO2, CO and O3. The obtained results have proved that the regions with similar air pollution characteristic can be appropriately grouped by applying cluster analysis. All 22 regions are classified into six groups, and the pollution pattern for each group is characterized as: Group 1 (high SO2/NO2; low PM10), Group 2 (high PM10), Group 3 (high SO2/PM10), Group 4 (low SO2/NO2/CO; high O3), Group 5 (low CO/NO2; high O3) and Group 6 (low PM10/SO2/NO2/O3/CO). Results from air quality evaluation indicate that the regions in group 6 (Ilan, Hualien and Taitung) have the best air quality while the regions in group 3 (Kaohsiung and Kaohsiung City) have the worst air quality in Taiwan. The results from correlation analysis reveal that incidence of the respiratory system disease is significantly positively correlated with pollution of NO2 and CO at 99% confidence level.

Bioaerosols study in central Taiwan during summer season

Suspended particles, of which bioaerosols are one type, constitute one of the main reasons to cause severe air quality in Taiwan. Bioaerosols include allergens such as fungi, bacteria, actinomycetes, arthropods and protozoa, as well as microbial products such as mycotoxins, endotoxins and glucans. When allergens and microbial products are suspended in the air, local air quality will be influenced severely. In addition, when the particle size is small enough to pass through the respiratory tract entering the human body, the health of the local population is also threatened. Therefore, the purpose of this study attempted to understand the concentration and types of bacteria during summer period at four sampling sites in Taichung city, central Taiwan. The results indicated that total average bacterial concentration by using R2A medium incubated for 48 h were 7.3 x 10(2) and 1.2 x 10(3) cfu/m3 for Chung-Ming elementary sampling site during daytime and night-time period of summer season. In addition, total average bacterial concentration by using R2A medium incubated for 48 h were 2.2 x 10(3) and 2.5 x 10(3) cfu/m3 for Taichung refuse incineration plant sampling site during daytime and night-time period of summer season. As for Rice Field sampling site during daytime and night-time period of summer season, the results also reflected that the total average bacterial concentration by using R2A medium incubated for 48 h were 3.4 x 10(3) and 3.5 x 10(3) cfu/m3. Finally, total average bacterial concentration by using R2A medium incubated for 48 h were 1.6 x 10(3) and 1.9 x 10(3) cfu/m3 for Central Taiwan Science Park sampling site during daytime and night-time period of summer season. Moreover, the average bacterial concentration increased as the incubated time in a growth medium increased for particle sizes of 0.65-1.1, 1.1-2.1, 2.1-3.3, 3.3-4.7 and 4.7-7.0 microm. The total average bacterial concentration has no significant difference for day and night sampling period at any sampling site for the expression of bacterial concentration in term of order. The high average bacterial concentration was found in the particle size of 0.53-0.71 mm (average bioaerosol size was in the range of 2.1-4.7 microm) for each sampling site. Besides, there were exceeded 20 kinds of bacteria for each sampling site and the bacterial shape were rod, coccus and filamentous.

Evaluating Taiwan's air quality variation trends using grey system theory

According to geographical characteristics and air quality conditions, the Taiwan Environmental Protection Agency has divided the island into 7 air quality regions (AQRs) including Northern, Chu‐Miao, Central, Yun‐Chia‐Nan, Kao‐Ping, I‐lan and Hwa‐Tung AQRs. The grey relational grade (GRG) of all AQRs and nationwide grade were calculated to comprehend the level of contamination. Then the grey model GM (0, N) was used to evaluate the effects of 5 primary contaminants on air quality. The results indicated that the ranking of air quality for the 7 AQRs from the best to the worst were as follows: Hwa‐Tung > I‐lan > Chu‐Miao > Northern > Yun‐Chia‐Nan > Central > Kao‐Ping. The 5 most common contaminants from the greatest to the least were as follows: CO > SO2 > NO > O3 > PM10.

Evaluation of the Trend of Air Quality in Taipei, Taiwan from 1994 to 2003

The data collected from the five air quality monitoring stations established by the Taiwan Environmental Protection Administration (TEPA) in Taipei City were analyzed to assess the changes in air quality. The analyses reveal that the air quality in Taipei City improved over the last decade from 1994 to 2003, as evidenced by the significant downward trends of the various primary air pollutant concentrations, such as CO, NO(X), SO(2), and PM(10). An air pollution fee was collected by TEPA in 1995, and several air pollution control measures were likewise taken to improve the air quality in Taiwan. However, although the extreme daily maximum O(3) concentrations occurred more frequently in earlier years and showed a downward trend, its moderately high concentrations increased annually in recent years. It implied that after the reduction of various primary pollutant concentrations, the effective reduction of O(3) pollution still remains an important issue.

Influence of Asian dust storms on air quality in Taiwan

In each year, dust storms triggered by cold air masses passing through northern China and Mongolia enhance the PM10 concentration over Taiwan region during winter and spring. On average, there are four to five dust events and 6.1 dust days in a year in Taiwan. Each event lasts for 1 day or even longer. A procedure to identify a dust event is rationalized and exercised on data collected during 1994–2005. Also, a ranking method named as the dust intensity rank (DIR) is developed to distinguish the intensity of each event affecting the local air quality. About 86% of dust days belong to ranks 1 and 2. In general, poorer air quality is associated with higher ranks. Ranks 4 and 5 correspond to a PSI (Pollution Standard Index) larger than 100. Linking DIR with the popular PSI is useful for both the public and the official forecasting system. It is also useful for inter-comparison between dust influences on air quality at different downstream regions in Taiwan. Composite analyses of the temporal and spatial variation of the hourly PM10 level indicate that dust particles usually arrive 12 h before the time of the peak PM10 concentration and last for 36 h at northern Taiwan, while the time of the peak concentration at eastern or western Taiwan, due to the evolution of the synoptic weather system, is about 3–12 h later. It is noted that the increase of PM10 level at the western side of Taiwan results from a mixture of upstream Asian dust inputs and local pollutants.

Aerosol characteristics from the Taiwan aerosol supersite in the Asian yellow-dust periods of 2002

The occurrence of Asian dust storms, and the subsequent transport of yellow dust (YD) greatly influences the air quality of lee-side countries such as Korea and Japan. The dust is also frequently transported in a southward direction by a strong cold high-pressure system that affects the air quality in Taiwan. This study reports the aerosol properties that were monitored continuously at the Taiwan aerosol supersite during YD events in 2002. Based on the observations of meteorology and aerosols, we divided the time interval of a YD event into a before period, during period, and after period. Among the seven observed YD events, the second event was marked with the maximum hourly PM 10 level at 502 μg m −3, and with the longest during period for a total of 147 h. The averages of the hourly PM 10 and PM 2.5−10 were much higher in the during period as compared to those in the before period. It is interesting to note that the time lapse in the during period was well correlated with the maximum level of both PM 10 and PM 2.5−10. It must be noted that the PM 2.5 levels were dramatically increased in the after period, which was due to the accumulation of particles influenced by the anticyclonic outflow. The aerosol size distribution in the third YD event verified that supermicron particles dominated in the during period, and that submicron particles were predominant in the before and after periods. For the chemical properties of the aerosols, time series results indicated that sulfates were mostly contributed by the dust transport, and the others were more related to vehicle exhausts. However, they all accumulated in the period of atmospheric stagnancy.

Long-range transport of aerosols and their impact on the air quality of Taiwan

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 30 μg m −3 to the PM 10 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 SO 2 are about 230 and 0.5 ppb, respectively. The identified, dust events have the highest average inflow concentration (about 71±34 μg m −3) of PM 10. The dust impacts on PM 10 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 SO 2, 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.