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Cloud macrophysics schemes are unique parameterizations for general circulation models. We propose an approach based on a probability density function (PDF) that utilizes cloud condensates and saturation ratios to replace the assumption of critical relative humidity (RH). We test this approach, called the Global Forecast System (GFS) – Taiwan Earth System Model (TaiESM) – Sundqvist (GTS) scheme, using the macrophysics scheme within the Community Atmosphere Model version 5.3 (CAM5.3) framework. Via single-column model results, the new approach simulates the cloud fraction (CF)–RH distributions closer to those of the observations when compared to those of the default CAM5.3 scheme. We also validate the impact of the GTS scheme on global climate simulations with satellite observations. The simulated CF is comparable to CloudSat/Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data. Comparisons of the vertical distributions of CF and cloud water content (CWC), as functions of large-scale dynamic and thermodynamic parameters, with the CloudSat/CALIPSO data suggest that the GTS scheme can closely simulate observations. This is particularly noticeable for thermodynamic parameters, such as RH, upper-tropospheric temperature, and total precipitable water, implying that our scheme can simulate variation in CF associated with RH more reliably than the default scheme. Changes in CF and CWC would affect climatic fields and large-scale circulation via cloud–radiation interaction. Both climatological means and annual cycles of many of the GTS-simulated variables are improved compared with the default scheme, particularly with respect to water vapor and RH fields. Different PDF shapes in the GTS scheme also significantly affect global simulations.

A new k-distribution scheme of longwave radiation without the correlated-k-distribution assumption is developed. Grouping of spectral points is based on the line-by-line (LBL)-calculated absorption coefficient k at a few sets of reference pressure pr and temperature θr, where the cooling rate is substantial in a spectral band. In this new scheme, the range of k(pr, θr) of a band is divided into a number of equal intervals, or g groups, in log10(kr). A spectral point at the wavenumber ν is identified with one of the g groups according to its kν(pr, θr). For each g group, a Planck-weighted k-distribution function Hg and a nonlinearly averaged absorption coefficient k¯g⁡(p,θ) are derived. The function Hg and the absorption coefficient k¯g⁡(p,θ) constitute the new k-distribution scheme. In this k-distribution scheme, a spectral point can only be identified with a g group regardless of pressure and temperature, which is different from the correlated-k distribution scheme. The k-distribution scheme is applied to the H2O, CO2, O3, N2O, and CH4 absorption bands, and results are compared with LBL calculations. To balance between the accuracy and the computational economy, the number of g groups in a band of a given gas is chosen such that 1) the difference in cooling rate is

The seasonal prediction of the Indian summer monsoon (ISM) and Monsoon Intraseasonal Oscillations (MISO), as well as the Madden Julian Oscillations (MJO) that strongly modulate MISO, is of much importance to the agriculture sectors of the Indian Sub‐continent. This study highlights the importance of selecting proper “autoconversion” coefficients for precipitation formation in Coupled Global Climate Model's convective and microphysical schemes in simulating MISO and MJO. With a series of sensitivity experiments, we systematically examined the convective autoconversion and microphysical autoconversion coefficients in the National Centers for Environmental Prediction Coupled Forecast System version 2 (CFSv2). The mean and intraseasonal features of MISO and MJO are improved with a proper combination of autoconversion coefficients, which not only provide a better partition of cloud water and ice but also better feedback between the large‐scale condensation and convective parameterization. The results demonstrate a road map for the improvement of MISO as well as MJO simulation using a coupled climate model.

This study investigated the influence of holiday characteristics and numbers of vacation days on the “holiday effect” of three crucial Chinese holidays in Taipei. Surface measurements of NOx, CO, NMHC, O3, SO2, and PM10 from 13 air quality-monitoring stations of the Taiwan Environmental Protection Administration (TEPA) in the Taipei metropolitan area during holiday and non-holiday periods of 1994–2012 were used. All six pollutants were proven to exhibit holiday effects between Chinese New Year (CNY) and non-Chinese New Year (NCNY) periods. However, almost all pollutants exhibited holiday effects for the two other holidays; the exceptions were O3 between Tomb Sweeping Day (TSD) and non-Tomb Sweeping Day (NTSD) periods and CO and PM10 between Mid-Autumn Day (MAD) and non-Mid-Autumn Day (NMAD) periods. Air pollutants, including NOx, CO, NMHC, SO2, and PM10, that exhibited holiday effects had consistently lower concentrations in holiday periods than in non-holiday periods, whereas O3 concentrations were higher in holiday periods than in non-holiday periods. A widespread holiday effect with consistent signs indicates a high degree of urbanization in the study area. Compared with CNY–NCNY and MAD–NMAD periods, the TSD–NTSD period had a considerably lower difference of the titration effect, lower NOx resulting in less ozone destruction, in evening traffic hours and an inconsistent holiday effect in the daytime and nighttime, leading to the lack of O3 holiday effect. Because the MAD period had more nighttime activities than the other two holiday periods did, the MAD–NMAD period lacked CO and PM10 holiday effects. The prevalently higher ratios of CO, NMHC, SO2, and PM10 relative to NOx as a proxy of mobile sources and a lower PM2.5/PM10 ratio in the MAD period than in the CNY and TSD periods indicate different pollution sources oriented from holiday activities. The air pollutants exhibited a weakening trend are all associated with a greater improvement in air quality during the non-holiday periods than the holiday periods, which implies successful air pollution control policies. Holiday effects of NOx, NMHC (p

This study evaluates the performance of the Taiwan Earth System Model version 1 (TaiESM1) in simulating the observed climate variability in the historical simulation of the Coupled Model Intercomparison Phase 6 (CMIP6). TaiESM1 is developed on the basis of the Community Earth System Model version 1.2.2, with the inclusion of several new physical schemes and improvements in the atmosphere model. The new additions include an improved triggering function in the cumulus convection scheme, a revised distribution‐based formula in the cloud fraction scheme, a new aerosol scheme, and a unique scheme for three‐dimensional surface absorption of shortwave radiation that accounts for the influence of complex terrains. In contrast to the majority of model evaluation processes, which focus mainly on the climatological mean, this evaluation focuses on climate variability parameters, including the diurnal rainfall cycle, precipitation extremes, synoptic eddy activity, intraseasonal fluctuation, monsoon evolution, and interannual and multidecadal atmospheric and oceanic teleconnection patterns. A series of intercomparisons between the simulations of TaiESM1 and CMIP6 models and observations indicate that TaiESM1, a participating model in CMIP6, can realistically simulate the observed climate variability at various time scales and are among the leading CMIP6 models in terms of many key climate features.

A new k-distribution scheme without the assumption of the correlation between the absorption coefficients at different pressures is developed for solar heating due to water vapor and CO2. Grouping of spectral points is based on the observation that radiation at spectral points with a large absorption coefficient is quickly absorbed to heat the stratosphere, and the heating below is attributable to the absorption of the solar radiation at the remaining spectral points. By grouping the spectral points with a large absorption coefficient at low pressures, the range of the absorption coefficient of the remaining spectral points is narrowed, and the k-distribution approximation can be accurately applied to compute solar heating in both the stratosphere and troposphere. Grouping of the spectral points is based on the absorption coefficient at a couple of reference pressures where heating is significant. With a total number of 52 spectral groups in the water vapor and CO2 bands, fluxes and heating rates were calculated for various solar zenith angles in some typical and sampled atmospheres in diverse climatic regimes and seasons. The maximum heating rate difference between the k-distribution and line-by-line calculations is < 0.09 K day-1 for water vapor, and < 0.2 K day-1 for CO2. The difference in the surface radiation is ~ 1.4 W m-2 for water vapor and 0.6 W m-2 for CO2, while it could increase to 2.6 W m-2 due to overlapping absorption. These results can be improved by increasing the number of spectral groups at the expense of computational economy.

The Taiwan Earth System Model (TaiESM) version 1 is developed based on Community Earth System Model version 1.2.2 of National Center for Atmospheric Research. Several innovated physical and chemical parameterizations, including trigger functions for deep convection, cloud macrophysics, aerosol, and three-dimensional radiation–topography interaction, as well as a one-dimensional mixed-layer model optional for the atmosphere component, are incorporated. The precipitation variability, such as diurnal cycle and propagation of convection systems, is improved in TaiESM. TaiESM demonstrates good model stability in the 500-year preindustrial simulation in terms of the net flux at the top of the model, surface temperatures, and sea ice concentration. In the historical simulation, although the warming before 1935 is weak, TaiESM well captures the increasing trend of temperature after 1950. The current climatology of TaiESM during 1979–2005 is evaluated by observational and reanalysis datasets. Cloud amounts are too large in TaiESM, but their cloud forcing is only slightly weaker than observational data. The mean bias of the sea surface temperature is almost zero, whereas the surface air temperatures over land and sea ice regions exhibit cold biases. The overall performance of TaiESM is above average among models in Coupled Model Intercomparison Project phase 5, particularly that the bias of precipitation is smallest. However, several common discrepancies shared by most models still exist, such as the double Intertropical Convergence Zone bias in precipitation and warm bias over the Southern Ocean.

A new method has been developed to retrieve aerosol optical depth (AOD) from sunshine duration (SSD). Retrieved AODs from SSD at the six stations in northern China in 2003–2005 agree reasonably well with AODs retrieved from Moderate Resolution Imaging Spectroradiometer observations near the six stations. Values and trends in AOD retrieved from SSD in Beijing and Tianjin in the period 1961–2005 also agree with those retrieved from solar radiation and visibility. These agreements allow the retrieval of credible upper and lower limits for anthropogenic AODs from SSD at the six stations during 1961–2005. The trends in anthropogenic AODs are approximately a factor of 3 to 5 lower than the trends in emissions of gas-phase precursors of aerosols in 1973–2005, implying a significant sublinear relationship between the level of aerosols and emissions of their gas phase precursors. This finding has important implications for formulating a control strategy for PM2.5 or haze pollution in northern China.

Trends in precipitation are critical to water resources. Considerable uncertainty remains concerning the trends of regional precipitation in response to global warming and their controlling mechanisms. Here, we use an interannual difference method to derive trends of regional precipitation from GPCP (Global Precipitation Climatology Project) data and MERRA (Modern- Era Retrospective Analysis for Research and Applications) reanalysis in the near-global domain of 60°S–60°N during a major global warming period of 1979–2013. We find that trends of regional annual precipitation are primarily driven by changes in the top 30% heavy precipitation events, which in turn are controlled by changes in precipitable water in response to global warming, i.e., by thermodynamic processes. Significant drying trends are found in most parts of the U.S. and eastern Canada, the Middle East, and eastern South America, while significant increases in precipitation occur in northern Australia, southern Africa, western India and western China. In addition, as the climate warms there are extensive enhancements and expansions of the three major tropical precipitation centers–the Maritime Continent, Central America, and tropical Africa–leading to the observed widening of Hadley cells and a significant strengthening of the global hydrological cycle.

Significant increases of heavy precipitation and decreases of light precipitation have been reported over widespread regions of the globe. Global warming and effects of anthropogenic aerosols have both been proposed as possible causes of these changes. We examine data from urban and rural meteorological stations in eastern China (1955–2011) and compare them with Global Precipitation Climatology Project (GPCP) data (1979–2007) and reanalysis data in various latitude zones to study changes in precipitation extremes. Significant decreases in light precipitation and increases in heavy precipitation are found at both rural and urban stations, as well as low latitudes over the ocean, while total precipitation shows little change. Characteristics of these changes and changes in the equatorial zone and other latitudes suggest that global warming rather than aerosol effects is the primary cause of the changes. In eastern China, increases of annual total dry days (28 days) and ≥10 consecutive dry days (36%) are due to the decrease in light precipitation days, thereby establishing a causal link among global warming, changes in precipitation extremes, and higher meteorological risk of floods and droughts. Further, results derived from the GPCP data and reanalysis data suggest that the causal link exists over widespread regions of the globe.

In this work, 45 years (1961–2005) of hourly meteorological data in Taiwan, including temperature, humidity, and precipitation, have been analyzed with emphasis on their diurnal asymmetries. A long-term decreasing trend for relative humidity (RH) is found, and the trend is significantly greater in the nighttime than in the daytime, apparently resulting from a greater warming at night. The warming at night in three large urban centers is large enough to impact the average temperature trend in Taiwan significantly between 1910 and 2005. There is a decrease in the diurnal temperature range (DTR) that is largest in major urban areas, and it becomes smaller but does not disappear in smaller cities and offshore islands. The nighttime reduction in RH is likely the main cause of a significant reduction of fog events over Taiwan. The smaller but consistent reductions in DTR and RH in the three off-coast islands suggests that, in addition to local land use changes, a regional-scale process such as the indirect effect of anthropogenic aerosols may also contribute to these trends. A reduction in light precipitation (10 mm h−1) are found over Taiwan and the offshore islands. The changes in precipitation are similar to the changes of other areas in Asia, but they are different from those of the United States, Europe, and the tropical oceans. The latter do not show any reduction in light precipitation.

Measurements of speciated non-methane hydrocarbons (NMHCs) were conducted in an ozone non-attainment metropolis with pronounced industrial emissions in addition to traffic ones. Highly variable and complex natures of industrial sources make their composition profiles difficult to determine. In the circumstances of no reliable source profiles, two simple complementary approaches were attempted to characterize sources of NMHCs. First, a robust vehicular indicator, 3-methylpentane (3MC5A), which is an intrinsic component of gasoline, was used to estimate contributions of traffic versus non-traffic sources for major NMHCs with high ozone-forming potentials (OFPs), such as ethene, toluene, xylene, isoprene, etc. Second, the method of principal component analysis (PCA) was employed to further discern non-traffic emissions into various source groups. A total of 454 ambient samples were sampled in the urban-industrial complex metropolis (Kaohsiung, Taiwan) to build up a large dataset to be tested by the two complementary approaches. It was found that four types of emissions, i.e., traffic, household fuel leakage, industrial, and biogenic, were responsible for the observed ambient NMHCs. The industrial contribution was significant for ethene and toluene (with 48–67% and 33–62%, respectively), whereas xylene was found to be mainly vehicular. In addition, isoprene revealed its biogenic nature. OFPs arising from vehicular, industrial and biogenic contributions could be further assessed for the purpose of emission control of NMHCs in the ozone non-attainment area.

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.

An observation-based method (OBM) is developed to evaluate the ozone (O3) production efficiency (O3 molecules produced per NOx 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 NOx 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 10.273.9. The relationship of P(O3) with NOx 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 NOx. 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 observationbased 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. r 2007 Elsevier Ltd. All rights reserved.

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 O 3 +NO 2 ) 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.

Measurements of aerosols (PM1O) and other air pollutants at stations of the air quality monitoring network of Taiwan Environmental Protection Administration (EPA) from 1993 to 2000 are analyzed to evaluate the impact of Asian dust storm events on the air quality of Taiwan. Enhancements of PM10 at Yangming mountain station in northern Taiwan as well as coastal stations to the north and northeast turn out to be the key indicators in identifying unambiguously the major Asian dust storm events and to estimate the impact of these events on the PM10 over Taiwan. Our analysis shows that the major increases of PM10 at Yangming station occur in March, April, and May. They are clearly associated with the Asian dust storm events. On a yearly basis, the impact ranges from about 3% in southwestern cities to about 12% for Yangming station. On the monthly basis, the enhancements can be as large as 150% for a clean station such as Hengchun hear the southern tip of Taiwan. Although the major component of the observed PM10 enhancements is mineral dust, we estimate that sulfate and nitrate ions contribute to about one quarter of the enhancements. The corresponding enhancements for other air pollutants (i.e. CO, O3, NO2, and SO2) can be identified only occasionally because of high ambient values, large variability in concentrations, and other reasons.

In his comments, Wang cites a number of works to dispute the conclusion in our previous work, which attributes the observed decreases/increases in light/heavy precipitation in eastern China primarily to global warming rather than the regional aerosol effect. However, most of the cited works (admittedly, including our previous work), employ correlation analysis, which has little bearing on the cause–effect relationship. Theoretical analyses and/or modeling studies are needed to ascertain the cause–effect relationship. We argue that theoretical analyses and modeling results show that global warming is the primary cause of the widely observed phenomena of suppression of light precipitation and enhancement of heavy precipitation across the globe, including in eastern China.

[1] Daily data from reanalyses of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the National Centers for Environmental Prediction (NCEP) are analyzed to study changes in precipitation intensity with respect to global mean temperature. The results are in good agreement with those derived from the Global Precipitation Climatology Project (GPCP) data by Liu et al. (2009), providing an independent verification for large changes in the precipitation extremes: about 100% increase for the annual top 10% heavy precipitation and about 20% decrease for the light and moderate precipitation for one degree warming in the global temperature. These changes can substantially increase the risk of floods as well as droughts, thus severely affecting the global ecosystems. Atmospheric models used in the reanalysis mode, with the benefit of observed wind and moisture fields, appear to be capable of realistically simulating the change of precipitation intensity with global temperature. In comparison, coupled climate models are capable of simulating the shape of the change in precipitation intensity, but underestimate the magnitude of the change by about one order of magnitude. The most likely reason of the underestimation is that the typical spatial resolution of climate models is too coarse to resolve atmospheric convection.

[1] Data from the Global Precipitation Climatology Project (GPCP) covering the period 1979-2007 are examined for changes of precipitation extremes as a function of global mean temperature by using a new method which focuses on interannual differences rather than time series. We find that the top 10% bin of precipitation intensity increases by about 95% for each degree Kelvin (K) increase in global mean temperature, while 30%-60% bins decrease by about 20% K -1 . The global average precipitation intensity increases by about 23% K -1 , substantially greater than the increase of about 7% K -1 in atmospheric water-holding capacity estimated by the Clausius-Clapeyron equation. The large increase of precipitation intensity is qualitatively consistent with the hypothesis that the precipitation intensity should increase by more than 7% K -1 because of the additional latent heat released from the increased moisture. Our results also provide an independent evidence in support for significant increases in the number and/or size of strong global tropical cyclones. However an ensemble of 17 latest generation climate models estimates an increase of only about 2% K -1 in precipitation intensity, about one order of magnitude smaller than our value, suggesting that the risk of extreme precipitation events due to global warming is substantially greater than that estimated by the climate models.

[1] Total reactive nitrogen oxides (NOy) are among the key components in the chemistry of ozone production. In order to improve the understanding of the formation mechanisms of high-ozone events in Beijing, China, an intensive experiment on the reactive nitrogen oxides was carried out at the observatory of Peking University during the Campaign of Air Quality Research in Beijing and surrounding areas in 2006 (CAREBeijing-2006) campaign. In this study, analysis focusing on the data of high O3 episodes was performed to examine the relationship between the concentration of total oxidant and the composition of NOy. High levels of NO and NOy were observed in the morning rush hours, indicating the influences of fresh emissions from local traffic. However, the ratio of [NO] to [NOy] was only 11–60% in the morning, implying that there was a substantial amount of aged air pollutants remained overnight in the stagnant air mass. Significant increases in the NOz mixing ratio (= [NOy]-[NOx]) were observed during the period from the morning toward early afternoon, consistent with the increasing oxidant level. Ozone production efficiency of NOx (OPEx), which was derived from the NOz-Ox regression, was found to range from 3.9 to 9.7 mol/mol in Beijing. Furthermore, it was revealed that the daily [NOz] maximum was proportional to the NOx peak level in the morning, and that OPEx decreased with the increases of [NOz] in a hyperbolic form. According to the results, abatement in NOx emission would not be effective toward reducing ozone concentrations in Beijing.

Three years (2003-2005) of aerosol optical depths (AOD) measured with CIMEL sunphotometer were compared to the surface concentrations of PM10 and PM2.5 in Northern (i.e. Taipei) and Southern (i.e. Tainan) Taiwan. The correlation between AOD and PM10 is higher in Taipei than in Tainan. Additional chemical compositions of PM10 and PM2.5 in these two sites, including ionic component, sea salt, OC/EC and crustal components, were also examined to find their relationship with the AOD. These analyses indicate that aerosols in Taipei are mainly composed of fine aerosols, whereas in Tainan more crustal material and OC exist in the coarse mode, which partially explain the higher correlation of PM10 and AOD in Taipei. Closure calculations are carried out by combining data from lidar, sunphotometer, nephelometer, aethalomter, SMPS and APS size spectrometers, as well as chemical analyses of aerosols from PM10 and PM2.5 samplers and MOUDI impactor to investigate their consistency. The observed surface single scattering albedo was also compared to that retrieved by CIMEL sunphotometer, with additional discussion on the possible explanation to the discrepancies of the comparisons. Then, lidar measurement is applied to relate aerosols at the surface to those aloft.

Dust storms and long-range transport of pollutants are major environmental concerns of Taiwan during the winter monsoon season when northeasterly winds prevail following passages of cold fronts. To quantify the impact on air quality, we develop an objective method to classify and study the long-range transport processes by examining the frontal passages in two representative years. We have found that there is about one frontal passage per week in winter and spring, consistent with the climatological average. The long-range transport events are classified into three types according to their degrees of impact on levels of dusts and air pollutants in Taiwan, namely dust storms (DS), long-range transport with pollutants (FP), and long-range transport of background air masses (BG). DS cases occurred 4.7% of the time over 14 months and had a large average PM10 concentration of 127.6 μg m^(-3) at Wan-Li station. FP cases occurred 1.9% of the time and the mean concentration of PM10 during the FP periods was about 85 μg m^(-3). BG cases happened 18.6% of the time and the mean concentration of PM10 was 32.8 μg m^(-3). Dust storms and air pollutants tend to be transported in different air parcels as evidenced by a lack of correlation between dust aerosols and air pollutants. The frequency of local pollution (LP) cases was 71.7% in winter and spring. The average PM10 concentration of LP cases at the Wan-Li station was 47.4 μg m^(-3). However, about one to two-thirds of the PM10 during LP cases can be attributed to the long-range transport. When this contribution is taken into account, we estimate that the contribution of long-range transport to PM10 abundance in northern Taiwan during winter and spring to be in the range of 50% to 75%.

Long-term records (about 100 years) of meteorological parameters of Taiwan have been analyzed to study causes and implications of decreasing trends in sunshine duration observed during Taiwan's rapid economic developing period that started in the 1960's. Although the largest decreasing trends in sunshine duration are found in major urban centers, in-depth analysis shows that the reductions are surprisingly uniform and well correlated among stations throughout Taiwan and her surrounding islands, implying that direct scattering by aerosols is not the major cause of the reductions. Similar reductions occur at two high altitude stations, namely Alishan (2.4 km) and Yushan (3.85 km), suggesting that the cause of the reductions is at altitude above 3.85 km. After eliminating other potential causes, we hypothesize that the trends are most likely caused by an increase in regional clouds and/or cloud albedo as a result of increased anthropogenic aerosols. The extent of the region depends on the season. Strong westerlies above 3.85 km in winter and spring imply that southern China, Southeast Asia, India and regions further upwind may suffer similar reductions and could be the major source of anthropogenic and fall, the wind pattern indicates Taiwan's own emissions of aero sols can play a significant role in the reduction. Potential ramifications of the increase in clouds/cloud albedo to regional climate change are serious. The increase in clouds/cloud albedo obviously has lead to a decrease in the diurnal temperature range. These changes may also be linked to an in﹒ crease in precipitation intensity and other observed changes in some key climate parameters in Taiwan.