Research

[Abstract]  Information about the stable isotopocules of water is useful for understanding the water cycle. In conventional atmospheric models, isotope exchange between liquid and gas phases is usually assumed to be in equilibrium, and the highly kinetic phase transformation processes inferred in clouds are yet to be fully investigated. Here we show that different factors controlling isotopic composition, including water vapor sources, atmospheric transport, phase transition pathways of water in clouds, and kinetic versus equilibrium mass transfer, contributed significantly to the variations in isotope composition. The results suggest that future modeling should include the kinetic mass transfer process in microphysical calculation, as well as more observational data for model initialization. 

Tsai, I-C., W.-Y. Chen, J.-P. Chen, and M.-C. Liang, 2019: Kinetic mass-transfer calculation of water isotope fractionation due to cloud microphysics in a regional meteorological model, Atmos. Chem. Phys., 19, 1753-1766. 

[Abstract] Develop a statistical-numerical aerosol parameterization (SNAP) scheme to describe the physical processes of aerosol particles and their interactions with hydrometeors.  Compared with numerical solutions, analytical solutions and binned aerosol model simulations, the SNAP performs well, with higher accuracy and less computation time than high-order-numerical-quadrature technique. 

Chen, J.-P., I-C. Tsai, and Y.-C. Lin, 2013: A statistical–numerical aerosol parameterization scheme, Atmos. Chem. Phys., 13, 10483-10504, doi:10.5194/acp-13-10483-2013. 

We employed the SNAP scheme in the Taiwan Earth System Model (TaiESM), which is primarily developed by RCEC.  Unlike the two-moment schemes, which are widely used in conventional global models, the three-moment (0th, 2nd and 3rd moments) approach adopted in SNAP can represent the aerosol distribution without other assumptions. The TaiESM was verified with observations and subsequently used to tackle the impact of aerosols and clouds on the weather and climate system. The TaiESM is registered as one of the models in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the TaiESM paper has been submitted to the GMD journal. 

[Abstract] Improving a bin model to simulate the cloud particle formation in Titan’s atmosphere.  Compared with laboratory results, this study suggests that CH4-N2 binary nucleation is an important mechanism for cloud formation occurring on Titan. 

Tsai, I-C., M.-C. Liang, and J.-P. Chen, 2012: Methane-Nitrogen binary nucleation: a new microphysical mechanism for cloud formation in Titan's atmosphere.  Astrophys. J., 747. 

[Abstract] Apply the homemade aerosol parameterization SNAP to a regional air quality model CMAQ and investigate the impacts of aerosol mixing state on radiative and microphysical properties.  The simulation results show that the mixture process can reduce the overall single scattering albedo by up to 10% during a dust event.  In addition, the ability of aerosol particles to serve as Köhler theory cloud condensation nuclei increased over downwind areas and the ability to serve as ice nuclei may decrease or increase at low or high sub-zero temperatures, respectively, due to the switching from deposition nucleation to immersion freezing or haze freezing. 

Tsai, I-C., J.-P. Chen, Y.-C. Lin, C C.-K. Chou, and W.-N. Chen, 2015: Numerical investigation of the coagulation mixing between dust and hygroscopic aerosol particles and its impacts. 

Lung, S.-C., S.-W. Chou, J.-P. Chen, P.-C. Wen, H.-J. J. Su, I-C. Tsai, and Y.-S. Shen, 2018: Science Plan of “Climate Change and Health Adaptation”, Journal of Taiwan Land Research, 21, 2, 209-239 (in Chinese).

[Abstract] By investigating data during 2004-2015, this study explored the dynamic mechanisms of seasonal control of air quality over southern and northern Taiwan. Overall, higher (lower) pollution frequencies were observed in dry (wet) stages. Analysis of seasonality further suggested that pollution over southern Taiwan exhibited a symmetric characteristic, and that tropical modulation was a driving factor, whereas pollution over northern Taiwan displayed an asymmetric seasonality and likely followed the asymmetric East Asian seasonality. With the retreat of summer monsoon, air quality in southern Taiwan entered a poor phase rapidly; by contrast, good air quality was observed over northern Taiwan, which was due to the gradual southward migration of the western North pacific (WNP) high. Detailed dynamic processes contributing to atmospheric conditions and large-scale circulation were further compared between pollution and nonpollution cases. During dry stages, the midlatitude perturbations observed as wavy patterns had downstream effects on the atmospheric condition in Taiwan. The downstream effect of the midlatitude wave activity on air pollution was obviously found in the Dry Northerly stage in northern Taiwan and the Dry Southerly stage in southern Taiwan. In contrast to poor air quality during dry stages, air pollution was rarely observed during wet stages. The strength and location of the WNP high, which can be involved in the formation of nearby tropical cyclones, may mainly influence air quality in Taiwan. 

Wu, C.-H., I-C. Tsai, P.-C. Tsai and Y.-S. Tung, 2019: Large-Scale Seasonal Control of Air Quality in Taiwan, Atmospheric Environment, 116868.

[Abstract]  The Community Earth System Q3 Model is used to study the aerosol climate effects during the 1980s and 1990s in which the anthropogenic SO2 emissions decreased in North America and Western Europe and increased in East and South Asia. From the 100 year simulations, aerosol forcing results in cooler (0.13K) and drier (0.01mm/d) atmosphere with less short wave radiation flux at the surface (0.37W/m2). The clear-sky shortwave radiation flux decreased over East Asia (0.81W/m2) and South Asia (1.09W/m2), but increased over Western Europe (+1.16W/m2) and North America (+0.39W/m2), consistent with aerosol loading changes. While changes in spatial distributions of all-sky short wave radiation and surface temperature  are closely related to cloud changes, the changes in wind and precipitation do not correspond to aerosol loading changes, indicating the complexity of aerosol-cloud circulation interactions. The East and South Asia monsoons were generally weakened due mainly to southward shift of the 200hPa East Asia Jet (EAJ) and decrease in 850hPa winds; annual precipitation decreased by 2% in South Asia but increased by 2% in Yangtze-Huai River Valley over East Asia. The uncertainties associated with aerosol climate effects are addressed within the context of model variability and the global warming effect. For the latter, while the aerosol effects decrease the greenhouse warming on the global mean, the regional responses are different. Nevertheless, the characteristics of aerosol climate effects, including the southward 200hPa EAJ and weakened South Asia monsoon, still persist when the climate becomes warmer, although the strength and the geographical distribution are slightly modulated.

Tsai, I-C.*, W.-C. Wang, H.-H. Hsu, and W.-L. Lee, 2016: Aerosol effects on summer monsoon over Asia during 1980s and 1990s, J. Geophys. Res. Atmos., 121, 11761–11776, doi:10.1002/2016JD025388. 

[Abstract] The influence of present-day anthropogenic aerosols on the summer monsoon over the East Asia region was simulated using the Community Earth System Model coupled with a slab ocean model. The simulations revealed significant radiative forcing from anthropogenic aerosols and associated changes in clouds over East Asia and the northwestern Pacific; however, their spatial patterns differed from the exhibited surface temperature and precipitation responses. Two major dynamic feedback mechanisms were identified to explain such discrepancies. The wind–evaporation–sea surface temperature (WES) feedback, triggered by an initial cooling over the midlatitude sea surface, induced an equatorward expansion of ocean cooling through strengthened trade winds. The sea surface cooling excited a meridional wave pattern similar to the Pacific– Japan teleconnection pattern. Although the aerosol effect generally caused weakening in summer monsoon strength and regional precipitation over East Asia, precipitation increases were seen over the locations of the midlatitude mei-yu front and around the tropics. These precipitation increases are primarily associated with the WES feedback and teleconnection patterns. The aerosol effect also reached the upper troposphere, causing an equatorward shift of the jet stream over East Asia and the northwestern Pacific, indicating a much broader scale of teleconnection.

Chen, J.-P, I-J. Chen and I-C. Tsai, 2016: Dynamic feedback of aerosol effect on the East Asian summer monsoon. Journal of Climate, 29(17):6137-6149. 

[Abstract] The sulfur cycle and radiative effects of sulfate aerosol on climate are studied with a Global tropospheric Climate-Chemistry Model in which chemistry, radiation and dynamics are fully coupled. Production and removal mechanisms of sulfate are analyzed for the conditions of natural and anthropogenic sulfur emissions. Results show that the 1985 anthropogenic emission tripled the global SO2 and sulfate loadings from its natural value of 0.16 and 0.10TgS, respectively. Under natural conditions, the fraction of sulfate produced in-cloud is 74%; whereas with anthropogenic emissions, the fraction of in-cloud sulfate production slightly increased to 76%. Lifetimes of SO2 and sulfate under polluted conditions are estimated to be 1.7 and 2.0 days, respectively. The tripling of sulfate results in a direct radiative forcing of −0.43Wm−2 (clear-sky) or −0.24Wm−2 (all-sky), and a significant first indirect forcing of−1.85Wm−2, leading to a mean global cooling of about 0.1K. Regional forcing and responses are significantly stronger than the global values. The first indirect forcing is sensitive to the relationship between aerosol concentration and cloud droplet number concentration which requires further investigation. Two aspects of chemistry-climate interaction are addressed. Firstly, the coupling effects lead to a slight decrease of 1% in global sulfate loading for both the cases of natural and anthropogenic added sulfur emissions. Secondly, only the indirect effect of sulfate aerosols yields significantly stronger signals in changes of near surface temperature and sulfate loading than changes due to intrinsic climate variability, while other responses to the indirect effect and all responses to the direct effect are below noise level. 

Tsai, I-C., J.-P. Chen, P.-Y. Lin, W.-C. Wang and I. S. A. Isaksen, 2010:  Sulfur cycle and sulfate radiative forcing simulated from a coupled global climate-chemistry model.  Atmos. Chem. Phys., 10, 3693-3709.

[Abstract] Dust storms that occurred in East Asia during the spring of 2002 and 2003 were simulated by a regional dust deflation and transport model. Particular focus was placed on dust incursion events over Taiwan. Two of the events were analyzed in detail to give a complete picture of the three dimensional transport patterns. The general characteristics of dust incursion events were summarized, including the source locations, transport route and distribution pattern in three dimensions, traveling time, duration of incursion, and the seasonal spatial distribution of dust concentration. Significant differences were also found in these characteristics between the two years, the main cause of which was a change. in regional climate patterns. The performance of the model developed for this study was evaluated against other dust forecast models, and found to have superior capability for forecasting in the Taiwan area. 

Chen, J.-P., Z. Wang, C.-Y. Young, F. Tsai, I-C. Tsai, G.-J. Wang, W.-C. Shieh, H.-W. Lin, J.-Y. Huang, and M.-J. Lu, 2004: Simulations of Asian Yellow Dust Incursion Over Taiwan for the Spring of 2002 and 2003, Terrest. Atmos. Ocean. Vol 15, No. 5, 949-981. 

[Abstract] Evidences have showed that human health are affected by climate change in many ways. . Worldwide, governments are concerned about health impacts of climate change and the corresponding health adaptation strategies which should be supported by scientific evidences evaluating the interactions among variables of natural environment, man-made infrastructure, and health status. This paper presents a science plan for “Climate Change and Health Adaptation” considering the global trend of sustainability science, the policy needs of Taiwanese government, and the gaps of research findings.  Systems approach is used to evaluate the interactions among systems of natural environments, built environments, and health impacts; potential health  adaptation strategies could be identified  by interrupting the influential pathways among them.  Four research directions are proposed, namely (1) establishing integrated early warning systems to reduce health impacts, (2) exploring co-benefit strategies for health adaptation and mitigation of climate changes, (3) developing strategies of health promotion and health education with new types of scientific tools, and (4) building capacity for "climate changes and health adaptation". Moreover, solution-oriented, stakeholder-engaged, and integrated transdisciplinary collaboration should be encouraged in order to tackle the difficulty encountered in reality and reduce the health impacts of climate change effectively.  

Lung, S.-C., S.-W. Chou, J.-P. Chen, P.-C. Wen, H.-J. J. Su, I-C. Tsai, and Y.-S. Shen, 2018: Science Plan of “Climate Change and Health Adaptation”, Journal of Taiwan Land Research, 21, 2, 209-239 (in Chinese).

[Abstract] The prospective impacts of electric vehicle (EV) penetration on the air quality in Taiwan were evaluated using an air quality model with the assumption of an ambitious replacement of current light-duty vehicles under different power generation scenarios. With full EV penetration (i.e., the replacement of all light-duty vehicles), CO, VOCs, NOx and PM2.5 emissions in Taiwan from a fleet of 20.6 million vehicles would be reduced by 1500, 165, 33.9 and 7.2 Gg yr−1, respectively, while electric sector NOx and SO2 emissions would be increased by up to 20.3 and 12.9 Gg yr−1, respectively, if the electricity to power EVs were provided by thermal power plants. The net impacts of these emission changes would be to reduce the annual mean surface concentrations of CO, VOCs, NOx and PM2.5 by about 260, 11.3, 3.3 ppb and 2.1 μgm−3, respectively, but to increase SO2 by 0.1 ppb. Larger reductions tend to occur at time and place of higher ambient concentrations and during high pollution events. Greater benefits would clearly be attained if clean energy sources were fully encouraged. EV penetration would also reduce the mean peak-time surface O3 concentrations by up to 7 ppb across Taiwan with the exception of the center of metropolitan Taipei where the concentration increased by b2 ppb. Furthermore, full EV penetration would reduce annual days of O3 pollution episodes by ~40% and PM2.5 pollution episodes by 6–10%. Our findings offer important insights into the air quality impacts of EV and can provide useful information for potential mitigation actions.

Li, N., J.-P. Chen, I-C. Tsai, Q. He, S.-Y. Chi, Y.-C. Lin, and T.-M. Fu, 2016: Potential impacts of electric vehicles on air quality in Taiwan.  Science of the Total Environment, 566-567(2016), 919-928.

[Abstract] Based on the analysis of observational data obtained over a period of 17 years, this study developed a novel approach estimating long-term changes in the relative contributions of domestic and foreign sources to air pollution levels over the island of Taiwan. The contribution from foreign sources was calculated using data measured at selected coastal monitoring stations under specific meteorological conditions. The domestic contribution was derived by subtracting the foreign contribution from the overall concentration, which was calculated with island-wide monitoring station data averaged using Thiessen polygon area weighting. The trends of mean CO, NO, NO2 and SO2 concentrations in Taiwan were -2.1%, -3.3%, -1.4% and 0% yr-1; while the background concentrations varied by -1.0%, 5.7%, 3.8%and 6.6% yr-1, respectively. These figures suggest that the efforts of Taiwan in reducing air pollution are largely being negated by foreign contributions. Ozone showed a steady increase of 3.3% yr-1, and a portion of this was associated with a 1.0% yr-1 increase in background values. Local and background PM10 concentrations did not show significant long-term trends, but rather strong inter-annual variations associated with dust storm activity in East Asia. The domestic fractions of NO and NO2 respectively decreased from 90% and 85% in 1994 to less than 60% and 70% in 2010. In contrast, the domestic fraction of SO2 decreased from 82% in 1994 to 27% in 2010. The domestic fraction of CO exhibited no obvious trend due to concurrent decreases in local and background contributions. Background O3 values tended to drop across Taiwan due to the titration effect from domestic NO emissions, and the fraction of do-mestic O3 titration decreased from 50% in the mid-90s to 25% in 2010.

Chen, J.-P., C.-E. Yang and I-C. Tsai, 2015: Estimation of foreign versus domestic contributions to Taiwan's air pollution. Atmospheric Environment, 112,9-19, doi:10.1016/j.atmosenv.2015.02.022 

[Abstract] This study applied a regional air quality model, incorporated with an emission module, to quantitatively differentiate the atmospheric iron sources originating from lithogenic dusts or coal-burning fly ashes deposited in the Northwestern Pacific Ocean and its marginal seas. Particular attention was paid to the high iron content of fly ashes emitted from steel and iron plants burning coals. Using the year 2007 as an example, the modeling results exhibit large seasonal variations in iron deposition, with highest deposition fluxes occurred during spring and autumn, which are comparable to the seasonal fluctuation of chlorophyll a concentrations estimated by satellite images in the oceanic regions. Fly ash from coal burning accounted for 7.2% of the total iron deposited over the northwestern Pacific Ocean and 15% of that over the northern South China Sea. After considering the difference of iron solubility in the aerosols, anthropogenic aerosol associated with coal burning would be the major bioavailable iron source in the surface water of the oceanic regions.

Lin, Y.-C., J.-P. Chen, T.-Y. Ho and I-C. Tsai, 2015: Atmospheric Iron deposition in the Northwestern Pacific Ocean and its Adjacent Marginal Seas: the Importance of Coal Burning. Global Biogeochemical Cycles, 29, 139–159,  doi:10.1002/2013GB004795.