Columnar optical properties of tropospheric aerosol by combined lidar and sunphotometer measurements at Taipei,Taiwan

Vertical extinction profiles and columnar optical properties (optical depth, Angstrom exponent, lidar ratio, and particle depolarization) of aerosols were obtained by simultaneous measurements with a depolarization lidar and a sunphotometer at Taipei, Taiwan from February 2004 to January 2006. Columnar optical depths are high in Feb–Apr (0.61–0.75) by sunphotometer measurements. Lidar measurements show the contribution of aerosols in the free atmosphere on columnar optical depths are about 44–50% in Feb–Apr and about 26–37% in other months. Back-trajectory analyses and depolarization measurements show almost all of non-spherical aerosols originated from Northwest China which indicate Asian dusts frequently transported to Taipei from dust source regions in the free atmosphere. Aerosols with depolarization lower than 5% are found mostly originated from South China or Southeast Asia. Good correlations between columnar lidar ratio, particle depolarization, and Angstrom exponent are found for cases that columnar water vapor less than 1.5 cm. The effect of water vapor on particle depolarization is briefly discussed.     

Real-world vehicle emissions and VOCs profile in the Taipei tunnel located at Taiwan Taipei area

An in situ field experiment was conducted in a highway road tunnel in the Taipei City to determine the motor vehicle emission factors (EF) of different kinds of air pollution species. These are carbon monoxide (CO), oxides of nitrogen (NO_x), non-methane hydrocarbons (NMHC) and VOCs species. About 56 species of VOCs were sampled by canister sampler and followed by the GC-MS analyzing. Furthermore, the tunnel-drafting rate was determined by SF₆ tracer method.The EF for the highway vehicles determined from this experiment are 3.64, 0.90, 0.44 and 0.24 gm km⁻¹ veh⁻¹ for CO, NO_x, NMHC and the totally measured VOCs, respectively. A comparison of the EFs from the road tunnel experiment to the estimates by the USEPA MOBILE5b (M5b) and the modified Taiwan EPA MOBILE-TAIWAN2.0 (MT2.0) provides a first-hand evaluation of the model characteristics. M5b and MT2.0 both tend to underpredict CO by 10% and 20%, respectively. While M5b overpredicts NO_x and NMHC by 40% and 20%, respectively; MT2.0 has fairly good predictions for these two species. From the GC-MS analysis of the canister samples, it was found that the most abundant species from the traffic-emitted VOCs in Taipei road tunnel are toluene, ethene and 1,2,4-trimethyl-benzene (1,2,4-TMB) by the weight basis. However, ethene, acetylene and toluene are the most abundant in VOCs based on volume. The VOCs’ weight composition in terms of the carbon bond classification is 28% by the paraffins, 33% by the olefins and 39% by the aromatics, respectively. In order to evaluate the ozone formation potential from the typical road emission in Taipei area, the maximum increment reactivity is calculated. It was found that about 1015 mg of O₃ is induced by per vehicle per kilometer traveled emission. Among them, ethene, 1,2,4-TMB and propene from the road vehicle's emission contribute most to the ozone-formation reactivity.     

The continuous field measurements of soluble aerosol compositions at the Taipei Aerosol Supersite,Taiwan

The characteristics of ambient aerosols, affected by solar radiation, relative humidity, wind speed, wind direction, and gas–aerosol interaction, changed rapidly at different spatial and temporal scales. In Taipei Basin, dense traffic emissions and sufficient solar radiation for typical summer days favored the formation of secondary aerosols. In winter, the air quality in Taipei Basin was usually affected by the Asian continental outflows due to the long-range transport of pollutants carried by the winter monsoon. The conventional filter-based method needs a long time for collecting aerosols and analyzing compositions, which cannot provide high time-resolution data to investigate aerosol sources, atmospheric transformation processes, and health effects. In this work, the in situ ion chromatograph (IC) system was developed to provide 15-min time-resolution data of nine soluble inorganic species (Cl⁻, NO₂⁻, NO₃⁻, SO₄²⁻, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺). Over 89% of all particles larger than approximately 0.056 μm were collected by the in situ IC system. The in situ IC system is estimated to have a limit of detection lower than 0.3 μg m⁻³ for the various ambient ionic components. Depending on the hourly measurements, the pollutant events with high aerosol concentrations in Taipei Basin were associated with the local traffic emission in rush hour, the accumulation of pollutants in the stagnant atmosphere, the emission of industrial pollutants from the nearby factories, the photochemical secondary aerosol formation, and the long-range transport of pollutants from Asian outflows.     

Meteorologically adjusted trends of daily maximum ozone concentrations in Taipei,Taiwan

The meteorological conditions exert large impacts on ozone concentrations, and may mask the long-term trends in ozone concentrations resulting from precursor emissions. Estimation of long-term trends of ozone concentrations due to the changes in precursor emissions is important for corresponding control strategy. Multiple linear regression (method I), multilayer perceptron (MLP) neural network (method II) and Komogorov-Zurbenko (KZ) filter method plus MLP methodology (method III), are used to estimate the meteorologically adjusted long-term trends of daily maximum ozone concentrations by removing the masking effects of meteorological conditions in this study. The daily maximum ozone concentrations and relative meteorological variables were extracted from six air-monitoring stations in Taipei area from 1994 to 2001. The data collected during 1994–2000 period were used as modeling set and utilized to estimate the meteorologically adjusted trends, and the data of 2001 were used as the validation data. The meteorologically adjusted trends of ozone for these three methods were calculated and compared. The results show that both MLP and KZ filter +MLP models are more suitable than multiple linear regression for estimating the long-term trends of ozone in Taipei, Taiwan. The long-term linear trends of meteorologically adjusted ozone concentrations due to the precursor emissions show an increase trend at all stations, and the percent changes per year range from 1.0% to 2.25% during the modeling period in Taipei area.     

Chemical compositions and radiative properties of dust and anthropogenic air masses study in Taipei Basin, Taiwan, during spring of 2004

Asia is one of the major sources of not only mineral dust but also anthropogenic aerosols. Continental air masses associated with the East Asian winter monsoon always contain high contents of mineral dust and anthropogenic species and transported southeastward to Taiwan, which have significant influences on global atmospheric radiation transfer directly by scattering and absorbing solar radiation in each spring. However, few measurements for the long-range transported aerosol and its optical properties were announced in this area, between the Western Pacific and the southeastern coast of Mainland China. The overall objective of this work is to quantify the optical characteristics of different aerosol types in the Eastern Asian. In order to achieve this objective, meteorological parameters, concentrations of PM₁₀ and its soluble species, and optical property of atmospheric scattering coefficients were measured continuously with 1 h time-resolved from 11 February to 7 April 2004 in Taipei Basin (25°00′N, 121°32′E). In this work, the dramatic changes of meteorological parameters such as temperature and winds were used to determine the influenced period of each air mass. Continental, strong continental, marine, and stagnant air masses defined by the back-trajectory analysis and local meteorology were further characterized as long-range transport pollution, dust, clean marine, and local pollution aerosols, respectively, according to the diagnostic ratios. The aerosol mass scattering efficiency of continental pollution, dust, clean marine, and local pollution aerosols were ranged from 1.3 to 1.6, 0.7 to 1.0, 1.4 and 1.4 to 2.3 m² g⁻¹, respectively. Overall, there are two distinct populations of aerosol mass scattering efficiencies, one for an aerosol chemical composition dominated by dust (<1.0 m² g⁻¹) and the other for an aerosol chemical composition dominated by anthropogenic pollutants (1.3–2.3 m² g⁻¹), which were similar to the previous measurements with high degree of temporal resolution.     

Optical properties of tropospheric aerosols based on measurements of lidar,sun-photometer,and visibility at Chung-Li (25°N, 121°E)

We have used lidar, sun-photometer, and the visibility measurements to investigate the optical properties of aerosols in the lower air. The observations were performed at Chung-Li (25°N, 121°E) during the period of February 2002–May 2004. Combined data indicate that 40–50% of total extinction in the column air contributed by aerosols in 1–5 km. Seasonally, spring time extinction is higher than other seasons. However, the summer extinction is the highest below about 2 km. Sources for aerosols are determined by using satellite imageries and back trajectories. Aerosols backscattering ratio and depolarization ratio are then categorized based on their sources. We found that the largest optical thickness is biomass burning aerosols originated in Southeast Asia. The aerosols generated from Northern China transported by the high-pressure system in spring are usually dust with depolarization ratios in the range of 0.1–0.3, but varying backscattering coefficients. The aerosols optical characteristics will be useful for future understanding about their environmental and climate effects.     

Evaluation of solid waste management strategies in the Taipei metropolitan area of Taiwan

Municipal solid waste (MSW) management is a major concern for highly urbanized societies. Among proposed MSW management systems, regionalization programs generally have received considerable attention. This study analyzes real-world operational data to assess different MSW management policies, especially regionalization strategies, and their impact on MSW management systems in the Taipei metropolitan area. Linear programming is also used to identify the minimum costs sustained by each policy. The linear programming results show that regionalization programs are more economical and also improve incinerator operation efficiency. Sensitivity analysis indicates that the minimum treatment requirement of incinerators is a very sensitive influence on the MSW flows distributed through the entire region. The MSW of several "sensitive" administrative districts will be allocated to different treatment facilities according to different management strategies. A list of preferential sequences of MSW treatment and disposal facilities can also be identified by the model presented in this study. The results of this study may provide a useful tool for aiding decision-making related to real-world MSW management problems.     

Evaluation of Solid Waste Management Strategies in the Taipei Metropolitan Area of Taiwan

Abstract

Chenfang Lin is with the Department of Soil and Environmental Science at National Chung Hsing University.Municipal solid waste (MSW) management is a major concern for highly urbanized societies. Among proposed MSW management systems, regionalization programs generally have received considerable attention. This study analyzes real-world operational data to assess different MSW management policies, especially regionalization strategies, and their impact on MSW management systems in the Taipei metropolitan area. Linear programming is also used to identify the minimum costs sustained by each policy. The linear programming results show that regionalization programs are more economical and also improve incinerator operation efficiency. Sensitivity analysis indicates that the minimum treatment requirement of incinerators is a very sensitive influence on the MSW flows distributed through the entire region. The MSW of several “sensitive” administrative districts will be allocated to different treatment facilities according to different management strategies. A list of preferential sequences of MSW treatment and disposal facilities can also be identified by the model presented in this study. The results of this study may provide a useful tool for aiding decision-making related to real-world MSW management problems.     

Optical and microphysical properties of severe haze and smoke aerosol measured by integrated remote sensing techniques in Gwangju,Korea

Aerosol optical and microphysical parameters from severe haze events observed in October 2005 at Gwangju, Korea (35.10°N, 126.53°E) were determined from the ground using a multi-wavelength Raman lidar, a sunphotometer, and a real-time carbon particle analyzer and from space using satellite retrievals. Two different aerosol types were identified based on the variability of optical characteristics for different air mass conditions. Retrievals of microphysical properties of the haze from the Raman lidar indicated distinct light-absorbing characteristics for different haze aerosols originating from eastern and northern China (haze) and eastern Siberia (forest-fire smoke). The haze transported from the west showed moderately higher absorbing characteristics (SSA = 0.90 ± 0.03, 532 nm) than from the northern direction (SSA = 0.96 ± 0.02). The organic/elemental carbon (OC/EC) ratio varied between 2.5 ± 0.4 and 4.1 ± 0.7.     

Applying hourly measurements of meteorological data and aerosol soluble ions in Taipei Basin, Taiwan

This study applies observational data composed of hourly weather and aerosol to discuss the aerosol characteristics within different weather systems. Based on cluster analysis, spring weather in Taipei Basin 2004 was characterised as five weather systems: humid/low south wind speed, dry cold/high east wind speed, humid cold/east wind, dry cold/northeaster, and northwestern convection wind. Under the humid/low south wind speed and northwestern convection wind systems, there are predominant influences of local vehicle/motor pollutant emissions and secondary pollution on the air quality. Asian dust storms were usually occurred under the weather of dry cold/high east wind speed. The regional air quality is more acceptable during the period of prevalent humid cold/east wind and dry cold/northeaster.     

Emission inventory and sources of polycyclic aromatic hydrocarbons in the atmosphere at a suburban area in Taiwan

The application of a chemical mass balance air pollution model to ambient measurements of polycyclic aromatic hydrocarbons (PAHs) is presented. Sixteen air samples were collected at seven sites in a suburban area in Taiwan and analyzed for the concentration of 21 compounds between July 2001 and September 2001. Each ambient sample was evaluated for the PAH contribution from six sources (heavy oil combustion, natural gas combustion, coal combustion, diesel combustion, vehicles and municipal solid waste incinerator). Average predictions agree well with the emission inventory. By this method, the average contributions are 49%, 14%, 22%, 12%, and 2% from vehicles, heavy oil combustion, natural gas combustion, coal combustion and diesel combustion at these seven receptors. By far, vehicles are the major PAH emission sources and municipal solid waste incinerator is a minor contributor. The calculated result of particulate PAHs is compared with that of total (gaseous and particulate) PAHs. The estimate based on total PAHs is better than the estimate based on particulate PAHs only. Contributions of eight low reactive PAHs for the same emission sources and receptors were calculated. Atmospheric reactivity seems not a problem for source apportionment in this study.     

Optical and thermal characteristics of carbonaceous aerosols measured at an urban site in Gwangju,Korea, in the winter of 2011

Carbonaceous components (organic carbon [OC] and elemental carbon [EC]) and optical properties (light absorption and scattering) of fine particulate matter (aerodynamic diameter <2.5 μm; PM_2.5) were simultaneously measured at an urban site in Gwangju, Korea, during the winter of 2011. OC was further classified into OC1, OC2, OC3, and OC4, based on a temperature protocol using a Sunset OC/EC analyzer. The average OC and EC concentrations were 5.0 ± 2.5 and 1.7 ± 0.9 μg C m^?3, respectively. The average single-scattering albedo (SSA) at a wavelength of 550 nm was 0.58 ± 0.11, suggesting that the aerosols observed in the winter of 2011 had a local warming effect in this area. During the whole sampling period, “stagnant PM” and “long-range transport PM” events were identified. The light absorption coefficient (b_abs) was higher during the stagnant PM event than during the long-range transport PM event due to the existence of abundant light-absorbing OC during the stagnant PM event. In particular, the OC2 and OC3 concentrations were higher during the stagnant PM event than those during the long-range transport event, suggesting that OC2 and OC3 might be more related to the light-absorbing OC. The light scattering coefficient (b_scat) was similar between the events. On average, the mass absorption efficiency attributed to EC (σ_EC) was 9.6 m² g^?1, whereas the efficiency attributed to OC (σ_OC) was 1.8 m² g^?1 at λ = 550 nm. Furthermore, the σ_EC is comparable among the PM event days, but the σ_OC for the stagnant PM event was significantly higher than that for the long-range transport PM event (1.7 vs. 0.5).

Implications: Optical and thermal properties of carbonaceous aerosol were measured at Gwangju, and carbonaceous aerosol concentration and optical property varied between “stagnant PM” and “long-range transport PM” events. More abundant light absorbing OC was observed during the stagnant PM event.     

A study on the relationships of place attachment and individual attributes of residents in different vulnerable districts in Taipei,Taiwan

Environmental Science and Pollution Research - Under the impact of climate change, Taiwan, an island state, has faced the challenges of extreme weather events in recent years. Based on previous...     

Overall dry deposition velocities of trace elements measured at harbor and traffic site in central Taiwan

For reasonable and convenient assessments of the characteristics of the dry deposition velocities between Taichung harbor site and Wuchi town site in central Taiwan, the overall dry deposition velocities of several metallic elements were calculated as the particulate diameter (D(p)) distributions of large particles (D(p) > 10 microm), coarse particles (10 microm < D(p) < 2.5 microm), and fine particles (D(p) < 2.5 microm) based on the ambient measurements during March-December of 2004. In this work, the dry deposition fluxes showed the higher correlation with coarse particle concentrations than large particle concentrations; however, the least well correlation was observed between the dry deposition fluxes and the fine particle concentrations. The calculated best-fit overall dry deposition velocities obtained using coarse particle concentrations varied from approximately 0.2 cm s(-1) for Cr to 1.5 cm s(-1) for Pb and 0.2 cm s(-1) for Fe to 2.6 cm s(-1) for Pb at Taichung harbor and Wuchi town site, respectively. In general, the crustal elements had higher deposition velocities than anthropogenic elements. In addition, overall dry deposition velocities for crustal elements were higher in Wuchi town site than in Taichung harbor site. The results identified the dry deposition flux was mainly contributed from large and coarse particles due to their high deposition velocities. The results also indicated that the best approach to estimate overall dry deposition was by depending on the characteristics of particles with diameters larger than 2.5 microm.     

Temporal distribution and potential sources of atmospheric mercury measured at a high-elevation background station in Taiwan

Measurements of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM), and particulate mercury (PHg) have been conducted at Lulin Atmospheric Background Station (LABS) in Taiwan since April 2006. This was the first long-term free tropospheric atmospheric Hg monitoring program in the downwind region of East Asia, which is a major Hg emission source region. Between April 13, 2006 and December 31, 2007, the mean concentrations of GEM, RGM, and PHg were 1.73 ng m^?3, 12.1 pg m^?3, and 2.3 pg m^?3, respectively. A diurnal pattern was observed for GEM with afternoon peaks and nighttime lows, whereas the diurnal pattern of RGM was opposite to that of GEM. Spikes of RGM were frequently observed between midnight and early morning with concurrent decreases in GEM and relative humidity and increases in O₃, suggesting the oxidation of GEM and formation of RGM in free troposphere (FT). Upslope movement of boundary layer (BL) air in daytime and subsidence of FT air at night resulted in these diurnal patterns. Considering only the nighttime data, which were more representative of FT air, the composite monthly mean GEM concentrations ranged between 1.06 and 2.06 ng m^?3. Seasonal variation in nighttime GEM was evident, with lower concentrations usually occurring in summer when clean marine air masses prevailed. Between fall and spring, air masses passed the East Asian continent prior to reaching LABS, contributing to the elevated GEM concentrations. Analysis of GEM/CO correlation tends to support the argument. Good GEM/CO correlations were observed in fall, winter, and spring, suggesting influence of anthropogenic emission sources. Our results demonstrate the significance of East Asian Hg emissions, including both anthropogenic and biomass burning emissions, and their long-range transport in the FT. Because of the pronounced seasonal monsoon activity and the seasonal variation in regional wind field, export of the Asian Hg emissions to Taiwan occurs mainly during fall, winter, and spring.     

Aerosol optical,chemical and physical properties at Gosan,Korea during Asian dust and pollution episodes in 2001

In order to understand the influence of dust and anthropogenic pollution aerosols on regional climate in East Asia, we analyzed the aerosol optical, chemical and physical properties for two cases with high aerosol loading and assessed the radiative forcing of these cases. The 1st case study is a heavy dust episode (DE) in April (during ACE-Asia) 2001 and the 2nd case is a regional-scale pollution event in November 2001. The Ångström exponent (Å) for DE was 0.38 from sunphotometer measurements. The mean single scattering albedo (550 nm) at the surface reported during the pollution episode (PE, 0.88) was lower than that of DE (0.91). The concentrations of organic (OC) and elemental carbon (EC) measured during the PE were about 90% and 30% higher than DE. The aerosol mass scattering efficiency (α_s) of PE is a factor of about 2 higher than that of the DE. The difference in the mass absorption efficiency (α_a) of EC during DE and PE is small and within the measurement uncertainty. The diurnally averaged aerosol radiative forcing efficiency (ΔDFE, W m⁻² τ⁻¹) during DE is similar to results of other studies at Gosan.     

On the optical properties of the polluted Athens atmosphere,during May 1995

Using ground-based spectral solar extinction data taken over the Athens atmosphere, reduced (total minus Rayleigh) and aerosol (Angstrom) spectral optical depths of the atmosphere, have been retrieved, under different polluted conditions. The results suggest that the optical depth, on days with relatively low pollution, exhibits slight variation with wavelength denoting that aerosols deplete all wavelengths almost equally. In contrast, under dense pollution, small particles scattering and trace gases absorption, are the dominant processes, resulting in steeper optical depth’s slopes, mainly in the ultraviolet domain. The Angstrom’s parameters β and α were determined through a least-squares fitting method. The turbidity β coefficient always shows a temporal pattern with high values in the morning and afternoon and low values midday.     

Measurements of the physical properties of particles in the urban atmosphere

Measurements of the physical properties of particles in the atmosphere of a UK urban area have been made, including particle number count by condensation nucleus counters with different lower particle size cut-offs; particle size distributions using a Scanning Mobility Particle Sizer; total particle Fuchs surface area using an epiphaniometer and particle mass using Tapered Element Oscillating Micro-balance (TEOM) instruments with size selective (PM₁₀ and PM_2.5) inlets. Mean particle number counts at three sites range from 2.86×10⁴ to 9.60×10⁴ cm^-3. A traffic-influenced location showed a substantially higher ratio of particle number to PM₁₀ mass than a nearby background location despite being some 70 m from the roadway. Operating two condensation nucleus counters in tandem to determine particles in the 3–7 nm size range by difference showed signficant numbers of particles in this range, apparently related to homogeneous nucleation processes. Measurements with the Scanning Mobility Particle Sizer showed a clear difference between roadside size distributions and those at a nearby background location with an additional mode in the roadside samples below 10 nm diameter. Particle number counts were found to show a significant linear correlation with PM₁₀ mass (r²=0.44; n=44 for 24 h data at an urban background location), although during one period of high pollution a curvilinear relationship was found. Measurements of the diurnal variation in PM₁₀ mass, particle number count and Fuchs surface area show the same general pattern of behaviour of the three variables, explicable in terms of vehicle emission source strength and atmospheric dispersion, although the surface area growth was out of phase with the particle number and mass. It appears that particle number gives the clearest indication of recent road traffic emissions.     

Continuous measurements of aerosol physical properties in the urban atmosphere

Simultaneous continuous measurements have been made at an urban background site of PM₁₀ mass by Tapered Element Oscillating Microbalance, particle number density by condensation nucleus counter and Fuchs surface area using an epiphaniometer. Concurrent measurements of gaseous NO_x and CO have been used to indicate road traffic emissions, and data from a nearby meteorological station have been used for relative humidity, temperature and windspeed. The data indicate that particle number density is a far better indicator of traffic activity than PM₁₀ mass which is strongly influenced by a high background, and also tends to peak rather later than the gaseous pollutants and particle number, presumably as a result of advection of accumulation mode aerosol. PM₁₀ mass and Fuchs surface area generally show a very similar temporal trend, although there is a tendency for the ratio of surface area to dry particle mass to increase with relative humidity. The sampling period included bonfire night celebrations which caused substantial increases in all particle parameters, although the ratio of particle mass to number was considerably higher than for the morning rush hour road traffic-influenced peak.     

Attenuation of UV-B radiation in the atmosphere: Clouds effect,at Qena (Egypt)

The effects of clouds (amount, type and height) on the surface UV-B radiation have been investigated at Qena, Egypt (26°17′, 32°10′, 96 m asl) using 2 years data (2004–2005) carried out by South Valley University (SVU)-meteorological research station. Thus, the characteristics of cloud's statistical property during the study period were employed to evaluate the general feature of the region of this study. However, ≈86% of all the observations were ⩽2 octas and the overcast conditions (8 octas) were very rarely over the study region (only 0.2% of all cases). These observations included 10% low-level clouds, 3.16% mid-level clouds and 7.59% high-level clouds. The dominated types of these clouds are stratocumulus (8.9%) and cirrus (5.8%).The hourly values of cloudless sky UV-B radiation (UV-B₀) and consequently the cloud modification factor (CMF) were estimated. An empirical model was developed for CMF as a function of the amount of cloud at low- and mid-level and high-level clouds. The correlation coefficients were equal to 0.985 and 0.987, respectively. In addition, a general expression of the CMF for situations those are considered as the effect of different clouds was found. The efficiency of this model has been tested in combination with a cloudless sky empirical model using independent data set. For this purpose, the hourly values of UV-B at selected cloudless and cloudy days were estimated. A good agreement was observed between the measured and the predicted values of our model. The mean value of the correlation coefficients of these selected days was 0.98.In addition, the attenuation of UV-B radiation could be determined by considering low- and mid-level and high-level clouds. The reduction of UV-B radiation as a function of cloud amount was non-linear for the both cases. At cloud amount of 100%, UV-B radiation was reduced by 83% on average by the high-level clouds.