Taichung Basin Research Articles

Spatial-temporal evaluation of PM2.5 concentration for health risk reduction strategy development in a basin with different weather patterns

Identifying the contribution of pollution sources to the atmospheric environment is critical to make an effective pollution reduction strategy for controlling the regional air quality. Spatial-temporal distribution of pollutant patterns is not only determined by the emission rate of a pollution source, but also closely related to the location of an emission source, regional topography, and wind field conditions. To understand the spatial pattern of pollutants under different weather conditions and topographical factors, this study evaluated the impact of large-scale stationary pollution sources in Taichung Basin located in Central Taiwan on regional air quality using The Air Pollution Model (TAPM), in which different weather types were taken into considerations. Results show that the present TAPM model could accurately simulate 44.0–95.0% of 5 actual synoptic weather conditions, including Outer-region circulation from tropical depression system, Weak northeast monsoon, Anticyclonic Outflow, The westward extension of Pacific Anticyclone, and South-deflected airflow. The research results revealed that weather types and regional wind fields dominated the pollutant transport patterns, where the westward extension of the Pacific Anticyclone and South-deflected Airflow could deteriorate the convection-diffusive conditions, causing high pollution events for Taichung Basin. Based on the present results, the air pollutants transport patterns under different synoptic weather conditions could be used as practical information by decision-makers to develop efficient air quality control strategies in the future.

Spatial Conservation of Ecological Landscape-Hydrologic Responses to Land Use Change in Datu Tableland

Datu Tableland is located at the land of Taichung Basin and Taichung’s Western Coastal Plain in central Taiwan. It is a large Urban Green Corridors with multi-functions of Ecological Service. It was suffered by flooding happened by human-made activities such as the development of scientific industrial park in recent years. This research collects data from different government agencies, including remote sensed data, 2009 digital land use data, soil data to establish the model of analyzing the changes of Ecological Service. Through analyzing and interpreting these data this study produce the layer of vegetation coverage and water storage capacity. At the same time, this study use arcgis database to manage and analyze the files efficiently. Dividing Datu Tableland to three subwatersheds makes the distribution of the changing of land use meaningful. It indicates landscape effects hydrological index and ecological vegetation coverage actually. This paper also estimates potential maximum retention amount in three subwatersheds. The total water storage capacity are estimated along urbanization and industrial development. The process of quantifying the impacts of LULC changes on hydrology at different scales including geomorphological and hydrological scales provides quantitative information for making decisions for land and water resource management. This paper also links landscape ecological thinking and hydrological thinking to ecological service analysis. The anticipated benefits for flood reduction by water storage facilities may be also received.

Field Performance of Ground Anchors in Taichung Basin

This research carried out field tests on nine vertical anchors to investigate their behavior in gravel of Taichung Basin. An anchor can be categorized as a deep anchor when the free length Z exceeds 8D (D is the diameter of the anchor). The shape of the heave on the ground surface of a shallow anchor is similar to a normal distribution curve. The extended diameter of the heave was between 170 and 300 cm, which could be divided into two zones, primary and secondary, based on the failure mode of the ground. As the fixed length of a shallow anchor increased, the extended diameter also increased. The ultimate load of an anchor increased with the free length and, to a greater degree, with the fixed length of an anchor: a fixed length of only 3 m (D = 0.12 m) generated an ultimate load of over 1100 kN.

Stratigraphic Architecture and Lithofacies Analysis: Evidence for Development of the Pliocene-Holocene Taichung Foreland Basin, Central Taiwan

The Taichung foreland basin, sub-basin of the Taiwan foreland basin, has developed since Pliocene. We studied stratigraphic architecture and the lithofacies of the Taichung basin in detail. We recognized eleven lithofacies, which are grouped into ten facies associations. Based on facies association analysis, we suggest that the development of the Taichung basin can be divided into four stages accompanied by syn-depositional deformation characterized by westward propagating thrust faults.Prior to 2.78 Ma, the basin was characterized by offshore environment during underfilled stage. Later, the Shuangtung Fault located to the east of the Western Foothills began to thrust westward and uplifted the Tertiary strata, which supplied sediments to basin between the Shuangtung and Chelungpu faults in initial filled stage. About 1 Ma, the Chelungpu Fault started to thrust westward and uplifted the Western Foothills, which shed fluvial sediments to fill basin between the Chelungpu and Tachia faults. After 0.46 Ma, the Tachia Fault began to thrust westward and strata immediately to the east of the Tachia Fault were uplifted to form ramps, producing Houli and Tatushan tablelands. The basin-filling reached the overfilled stage when the Chingshui Coastal Plain is dominated with fluvial facies.The Taichung foreland basin is bounded by Tachia and Shuangtung faults with the Chelungpu Fault in the middle and formed by active, sequentially propagating westward thrust faults from Pliocene to Pleistocene. The youngest Tachia Fault carried the piggyback basin in front of the older Chelungpu Fault, representing similar style to piggyback basins of the Po Basin and the Ebro Basin in Europe.

Integrated chemical species analysis with source-receptor modeling results to characterize the effects of terrain and monsoon on ambient aerosols in a basin

This study integrated estimated oxidation ratio of sulfur (SOR) and oxidation ratio of nitrogen (NOR) with source-receptor modeling results to identify the effects of terrain and monsoons on ambient aerosols in an urban area (north basin) and a rural area (south basin) of the Taichung Basin. The estimated results indicate that the conversion of sulfur mainly occurs in fine particles (PM₂.₅), whereas the conversion of nitrogen occurs in approximately equal quantities of PM₂.₅ and coarse particles (PM₂.₅-₁₀). The results show a direct relationship for PM₂.₅ between the modeling results with SOR and NOR. The high PM₂.₅ SOR, NOR, and secondary aerosol values all occurred in the upwind area during both monsoons; this shows that the photochemical reaction and the terrain effect on the pollutant transmission were significant in the basin. Additionally, the urban heat island effect on the urban area and the valley effect on the rural area were significant. The results show that secondary aerosol in PM₂.₅-₁₀ contributed approximately 10 % during both monsoons, and the difference in the contribution from secondary aerosol between both areas was small. Vehicle exhaust emissions and wind-borne dust were two crucial PM2.5-10 contributors during both monsoons; their average contributions in both areas were higher than 34 and 32 %, respectively.

Effects of basin topography and monsoon conditions on transport and occurrence of atmospheric PCDD/Fs in the Taichung Basin

Topographical and meteorological factors, such as monsoons, can drastically affect ambient dioxin levels. In order to better understand these phenomena, four sampling lines (comprising 16 sampling sites) were selected in accordance with the topographical characteristics and the transport paths of the Taichung Basin. The ambient air samples were simultaneously collected according to US EPA TO-9A. Seventeen polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were analyzed by a high-resolution gas chromatograph/high-resolution mass spectrometer. Field measurements indicated that, during monsoons, PCDD/Fs concentrations varied from 128 to 4,230 fg m(-3). Two locations, the pass between two tablelands and the valley in front of a mountain, had the highest PCDD/Fs concentrations; those concentrations were about two to five times greater than the average concentration. There were 189 analyses of 11 kinds of PCDD/Fs emission sources used to develop emission fingerprints for a CMB8.2 simulation. Chemical mass balance (CMB8.2) model simulation with PCDD/Fs and surface wind field measurements were performed. Results of CMB8.2 modeling indicated that the major source of most sites was secondary copper smelting. The CMB8.2 model indicated the effects of hills and river valleys on pollutant transport. Results indicated that secondary copper smelting must be controlled to reduce the ambient concentrations of PCDD/Fs in the Taichung Basin.

Opportunity Efficiency - Use Uncertainty Analysis to Evaluate Risks in Construction

In central Taiwan, around the Taichung basin, the ground condition is boulders with red soils and high ground waterlevel. Local technicians have developed an unusual soil excavation method to build the so-called “soil retainingcolumns”. It is cheap, practical and highly efficient. However it is fraught with risk and uncertainty.In general, use of the injury severity method in occupational injury evaluation is a good solution. But, the method seemsunsuitable for high risk situation in construction sites. Traditionally, there are 3 excavation methods to frame the soilretaining piles. Their risk distributions are not similar. Thus, we can’t use the same safety investment budget when wechoose different excavation method. In this study, for increase the exactness of “risk quantity”, we focus on the different“risk distribution”. Based our risk evaluation of the “hazard uncertainty” concept and introducing the notion of“opportunity efficiency” to modify usage of the “risk severity” analysis; this concept will increase the accuracy ofsafety investment evaluations.

Vertical Profile of Ozone and Accompanying Air Pollutant Concentrations Observed at a Downwind Foothill Site of Industrial and Urban Areas

This study measured vertical distributions of ozone, sulfur dioxide, nitrogen oxide, carbon monoxide, six biogenic-related volatile organic compounds, wind vector, humidity and temperature within the Planetary Boundary Layer (PBL) below 1200 m using a tethered balloon sounding system at a downwind rural site in the Taichung Basin, Taiwan, during the 2002 summer. During ozone episodes, both nocturnal inversion and valley-mountain wind circulation were stronger than those during non-episode days. The observed vertical distributions of these pollutants indicate that the concentrations of carbon monoxide, nitrogen monoxide and biogenic volatile organic compounds decreased as the height increased. Conversely, the highest ozone concentrations were measured during early afternoon at heights of 100-600 m above ground level. Notably, these high ozone concentrations were normally accompanied by relatively higher concentrations of nitrogen dioxide and sulfur dioxide, but not carbon monoxide. From emission inventory, trajectory analysis and statistical analysis, all suggest that high-stack point sources have an important role in causing the summer ozone episodes. This suggestion is supported by 11-y summer data at three stations in the Basin. In addition, it is found that part of the early-afternoon surface ozone was from ozone stored aloft in the residue layer at heights above the nocturnal boundary layer of the preceding night.

Assessing the Relationship between Air Mass Age and Summer Ozone Episodes Based on Photochemical Indices

Although pollutant sources are usually in urban and industrialized areas, poor air quality is frequently encountered in downwind rural areas. This study utilized a tethered balloon to measure the pollutant concentrations in a downwind side (Caotun) of the Taichung Basin during the summer of 2002. Furthermore, an annular denuder system (ADS) was used to measure PM2.5 and gaseous pollutant concentrations. Concentrations of 55 VOCs species were measured continuously by a network of photochemical assessment monitoring stations in central Taiwan. This study discusses the correlation between the ozone concentration and the routes of an air mass during ozone episodes. Backward trajectory, ratio of particulate matter and photochemical indices were used to examine the aging degree of an air mass. During ozone episodes, the trajectory distribution had a clear sea-land breeze mechanism with a relatively slow wind speed, and the air mass primarily entered through the western coastal industrial area. Analytical results demonstrate that daytime ozone concentrations accompany HNO3 concentrations by photochemical reactions and depend on the previous night’s HNO2 concentration. The sulfur and nitrogen conversion ratios, and the photochemical indices (ethylbenzene/m,p-xylene, n-pentane/t-2-pentene and NO2/NO) increased with the ozone concentration. The downwind photochemical indices were strongly correlated with ozone concentration and were higher than those upwind. These phenomena indicate that the air mass during ozone episodes belongs to the “more aged” category.

Distribution of PM2.5 and Gaseous Species in Central Taiwan During two Chinese Festival Periods

Measurements of PM2.5 and acidic gases were conducted at an inland site of Taichung basin. The sampling site was Nantou, which is located at a distance of 25 km from the Taichung city. Nantou represents an inland area surrounded by Central Mountain Ranges and Baqua Hill. The sampling timings were in the month of April (during Tomb-Sweeping Festival) and in September (during Mid-Autumn Festival). PM2.5 samples were collected with an annular denuder system. Aerosol ionic species including sulfate (SO42−), nitrate (NO3−), ammonium (NH4+), chloride (Cl−), calcium (Ca2+), potassium (K+), and sodium (Na+) and gaseous nitric acid (HNO3), hydrochloric (HCl), and sulfur dioxide (SO2) were analyzed. Results showed that the average PM2.5 concentration were 41.3 μg m−3 during the Tomb-Sweeping Festival period and 65.3 μg m−3 during the Mid-Autumn Festival period. The major particle-phase ionic species was sulfate (SO42−) during both the Chinese Festival periods. Ozone concentration was higher during the Mid-Autumn Festival. Sulfate (SO42−) and nitrate (NO3−) concentrations were well correlated with daily maximum ozone (O3) concentration. The time weight mean concentration data showed that the increased concentration of gas-phase sulfur dioxide (SO2) and sulfate (SO42−) were transported from Taichung City, which is located close to the sampling site. Based on our above obtained results, the Mid-Autumn Festival period showed more anthropogenic impact on the aerosol and gaseous distribution favored by meteorological factors, higher ambient temperature, and wind direction.

S-Wave Velocity Structure of the Taichung Basin, Taiwan, Estimated from Array and Single-Station Records of Microtremors

The objective of this study is to estimate the S-wave velocity structure of the Taichung basin in a near-fault region, which is needed for strong-motion evaluation for the 1999 Chi-Chi earthquake. We have conducted array measurements of microtremors with a total of 12 arrays at four sites and single-station measurements of microtremors at 48 sites in and around the Taichung basin. Based on the Rayleigh- wave inversion technique using phase velocities estimated from array records of microtremors, we find that a thick layer (the thickness of about 1000 to 1400 m) with an S-wave velocity of VS 1100 m/sec exists in the east-central part of the Tai- chung basin. We estimate the thicknesses of sedimentary layers above the pre- Tertiary bedrock at 48 sites to fit calculated peak and trough frequencies of horizontal-to-vertical spectral ratios of Rayleigh waves to observed peak and trough frequencies, assuming the same S-wave velocities estimated using array records. The pre-Tertiary bedrock depth was estimated to be about 5 to 6 km in this region. The estimated thickness of the layer with VS 1100 m/sec is largest in the east-central part of the basin and rapidly decreases to less than 400 m in the northeastern and western parts inside the basin. The estimated S-wave velocity structures reasonably explain arrival time of initial P and S waves of aftershock records observed by Higashi et al. (2001).

Ozone distribution in coastal central Taiwan under sea-breeze conditions

Sea-breeze circulation influences ozone concentration differently for two types of synoptic winds across the westcentral coastal plain of Taiwan. During summer months, when the synoptic flow is southerly, a strong westerly sea-breeze confined to the lower 700–800 m produces a northeastward flow. Ozone concentration is low, with a core centered at about 100 m, leading to moderate ozone concentrations in the low population density northeastern foothills. In autumn (and spring), northerly synoptic winds of about the same strength combine with less energetic westerly sea breeze to produce a southeastward flow that carries higher ozone levels into the heavily populated Taichung basin. Ozone levels are high from 80 to 400 m, with a core up to 120 ppb from about 150 to 300 m, contributing to serious ozone episodes at the southern (downwind) end of the basin. Analyzing the backward trajectories and ozone concentration showed that the weak southeastward breeze is the dominant factor affecting the occurrence of high ozone events in the region. The horizontal distribution is based on 3 yr data obtained from a network of air-pollution monitoring sites in the study area, while the vertical data comes from two 2-day tethersonde experiments, measuring wind-speed, direction, temperature and humidity, NO, NO 2, NMHC and O 3, conducted during August and November 1999.

Synoptic weather patterns and their relationship to high ozone concentrations in the Taichung Basin

Frequent high ozone days (defined as daily maximum ozone concentration ⩾80 ppb) during recent years in the Taichung Basin have caused much concern. High ozone days occur mainly during autumn and spring. Statistically, there is no clear linear relationship between a single meteorological variable and ozone concentration. In this study, data from 1996–2000 has shown that high ozone concentrations occur during two types of synoptic weather patterns. The first type is a continental cyclone emanating from mainland China, the southern part of it swept towards Taiwan by easterly winds. The second pattern is a tropical depression moving northwards toward the region, the northern part of it affecting Taiwan via easterly winds. Both types cover Taiwan with easterly winds, which are blocked by the Central Mountain Ranges (altitude of 2000–3000 m). The ranges create lee cyclogenesis to the west, which is unfavorable for pollutant dispersion and leads to serious air pollution episodes. The statistical results of the synoptic weather patterns in relation to ozone concentrations are based on the 5 yr data (1996–2000). This was obtained from a network of air-pollution monitoring sites in the study area, while the vertical data come from two 3-day tethersonde experimental campaigns conducted during March and October 2000, measuring air pressure, air temperature, relative humidity, wind speed and direction, non-methane hydrocarbons, NO x and O 3.

Subgrade reaction and load-settlement characteristics of gravelly cobble deposits by plate-load tests

This paper presents the result of plate-load tests conducted on a gravelly cobble deposit in Taichung Basin, Taiwan. The geologic formation of the gravelly cobble deposit makes it very difficult to obtain large undisturbed samples for laboratory testing. These field tests provide an opportunity to examine the applicability of existing theories on bearing capacity and subgrade reaction in this geologic formation. The modulus of subgrade reaction is of particular importance in the local practice of designing high-rise buildings on mat foundations. The results of the plate-load tests on this soil deposit are analyzed and discussed.Key words: plate-load test, gravelly cobble deposit, modulus of subgrade reaction, bearing capacity.

Subgrade reaction and load-settlement characteristics of gravelly cobble deposits by plate-load tests

This paper presents the result of plate-load tests conducted on a gravelly cobble deposit in Taichung Basin, Taiwan. The geologic formation of the gravelly cobble deposit makes it very difficult to obtain large undisturbed samples for laboratory testing. These field tests provide an opportunity to examine the applicability of existing theories on bearing capacity and subgrade reaction in this geologic formation. The modulus of subgrade reaction is of particular importance in the local practice of designing high-rise buildings on mat foundations. The results of the plate-load tests on this soil deposit are analyzed and discussed.Key words: plate-load test, gravelly cobble deposit, modulus of subgrade reaction, bearing capacity.