Application of a Machine Learning Method for Prediction of Urban Neighborhood-Scale Air Pollution.

Urban air pollution has aroused growing attention due to its associated adverse health effects. A model which could promptly predict urban air quality with considerable accuracy is, therefore, important and will benefit the development of smart cities. However, only a computational fluid dynamics (CFD) model could better resolve the dispersion behavior within an urban canyon layer. A machine learning (ML) model using the Artificial Neural Network (ANN) approach was formulated in the current study to investigate vehicle-derived airborne particulate (PM10) dispersion within a compact high-rise-built environment. Various measured meteorological parameters and PM10 concentrations were adopted as the model inputs to train the ANN model. A building-resolved CFD model under the same environmental settings was also set up to compare its model performance with the ANN model. Our results showed that the ANN model exhibited promising performance (r = 0.82, fractional bias = 0.002) when comparing the > 1000 h PM10 measurements. When comparing the diurnal hourly measured PM10 variations in a clear-sky day, both the ANN and CFD models performed well (r > 0.8). The good performance of the CFD model relied on the knowledge of the in situ diurnal traffic profile, the adoption of suitable mobile source emission factor(s) (e.g., from MOBILE 6 and COPERT4), and the use of urban thermal and dynamical variables to capture PM10 variations in both neutral and unstable atmospheric conditions. These requirements/constraints make it impractical for daily operation. On the contrary, the ML (ANN) model adopted here is free from these constraints and is fast (less than 0.1% computational time relative to the CFD model). These results demonstrate that the ANN model is a superior option for a smart city application.

External Cesium-137 doses to humans from soil influenced by the Fukushima and Chernobyl nuclear power plants accidents: a comparative study.

External exposure to gamma-photon irradiation from soil contamination due to nuclear power plant (NPP) accidents has significant contribution to human radiation exposure in the proximity of the NPP. Detailed absorbed doses in human organs are rarely reported in the literature. We applied the Monte Carlo Neutron Particle (MCNP) transport code to calculate and compare the absorbed doses in different human organs. The absorbed doses by gamma-photon radiation were from cesium-137 (137Cs) in soil contaminated by the two major NPP accidents. More serious and wide-spread impacts of the Chernobyl NPP accident on soil contamination in Ukraine, Belarus, Russia and countries as far as Sweden and Greece were due to the inland location, radiative plume transport pathway and high 137Cs emission strength (9 times the Fukushima emission). Based on our MCNP calculations, the largest absorbed dose was found in skin. The maximum calculated external 137Cs annual effective dose received from the Chernobyl accident was 10 times higher relative to the Fukushima accident. Our calculated effective doses at various influenced areas were comparable to those available in the literature. The calculated annual effective doses at areas near the Fukushima and Chernobyl NPPs exceeded the ICRP recommendation of 1 mSv yr-1.

Relationship between pedestrian-level outdoor thermal comfort and building morphology in a high-density city.

Urban compact buildings impose large frictional drag on boundary-layer air flow and create stagnant air within the building environment. It results in exacerbating the street-level outdoor thermal comfort (OTC). It is common to perform in-situ measurements of the OTC in different urban forms and to study their relationship. However, it is impossible to do so from a planning perspective because of the absence of physical planned urban forms. Our objective was to quantify the thermal environment and OTC in different planned complex urban forms by well-validated numerical models. We coupled a computational fluid dynamics (CFD) model to an OTC (Rayman) model to study the OTC. The κ-ω SST turbulent model was adopted for the CFD simulations, with accuracy of the turbulent model validated by wind tunnel measurements. The highest calculated air temperature within the street canyon of a planned bulky urban form could reach more than 5 °C higher than the surrounding environment. Within the tested urban forms, our coupled model predicted mean radiant temperature comparable with measurements in the literature. The model also produced sensible street-level physiologically equivalent temperatures (PETs) when comparing with those listed in the human thermal sensation categories. In the morning, the predicted PETs within all the urban forms were lower than that in open areas, which indicated that the shading of buildings effectively reduced the PET increase due to solar irradiance. At noon, increases in PETs by more than 10 °C relative to the morning situation indicated that when the buildings acted as heat sources after insolation absorption, increase in the air temperature at the street intersection and in the street canyon made an important contribution to the receiver PETs. The reduction in building lengths and increase in the low-level porosity were the most effective ways to reduce the heat stress at the pedestrian-level.

Public health risk of mercury in China through consumption of vegetables, a modelling study.

Sample measurement of mercury (Hg) contents is a common method for health risk assessment of Hg through vegetable consumption in China. In the present work, we undertook the first modelling study which produced consistent health-risk maps for the whole eastern China. Regional maps of Probable Daily Intake (PDI) of Total mercury (THg) and Methylmercury (MeHg) over the studied area were produced, which were important for the researchers and policy-makers to evaluate the risk and to propose mitigation measures if necessary. The model predictions of air-borne Hg(0) concentrations agreed well with the observations and simulated Hg distribution over China as reported elsewhere. Our calculated PDIs of THg in vegetables were also comparable to those reported in the literature. There was 19% of the studied area with PDIs > 0.08µgkg-1 bw d-1 [half of the reference dose (RfD)]. The PDI for THg (MeHg) varied from 0.034 (0.007) to 0.162 (0.035)µgkg-1 bw d-1 with an average of 0.058 (0.013)µgkg-1 bw d-1. The highest calculated PDIs of THg over China was equal to the RfD, while the calculated PDIs of MeHg were well below the RfD of 0.1µgkg-1 bw d-1. The health risk was of concern through consumption of THg in leafy vegetables, rice/wheat and fish in Liaoning Provinces, Hunan, Zhejiang and Guizhou Provinces, with the associated PDIs exceeding the RfD. Despite this, the heath risk of MeHg exposure for the general population in southern China from the same foodstuff consumption was not a concern. The contribution of consumption through leafy vegetation should be considered when THg and MeHg exposures to the population are evaluated. The results improve our understanding in managing public health risk in China especially in large cities with high population, and thus have important contribution to enhance sustainable urbanization as one of the principle goals under the framework of the Nature-Based Solution (NBS).

Aerosol pollution and its potential impacts on outdoor human thermal sensation: East Asian perspectives.

Aerosols affect the insolation at ground and thus the Aerosol Optical Depth (AOD, a measure of aerosol pollution) plays an important role on the variation of the Physiological Equivalent Temperature (PET) at locations with different aerosol climatology. The aerosol effects upon PET were studied for the first time at four East Asian cities by coupling a radiative transfer model and a human thermal comfort model which were previously well evaluated. Evident with the MODIS and AERONET AOD observations, the aerosol pollution at Beijing and Seoul was higher than at Chiayi (Taiwan) and Hong Kong. Based on the AERONET data, with background AOD levels the selected temperate cities had similar clear-sky PET values especially during summertime, due to their locations at similar latitudes. This also applied to the sub-tropical cities. Increase in the AOD level to the seasonal average one led to an increase in diffuse solar radiation and in turn an increase in PET for people living in all the cities. However, the heavy aerosol loading environment in Beijing and Seoul in summertime (AODs > 3.0 in episodic situations) reduced the total radiative flux and thus PET values in the cities. On the contrary, relatively lower episodic AOD levels in Chiayi and Hong Kong led to strong diffuse and still strong direct radiative fluxes and resulted in higher PET values, relative to those with seasonal averaged AOD levels. People tended to feel from "hot" to "very hot" during summertime when the AOD reached their average levels from the background level. This implies that in future aerosol effects add further burden to the thermal environment apart from the effects of greenhouse gas-induced global warming. Understanding the interaction between ambient aerosols and outdoor thermal environment is an important first step for effective mitigation measures such as urban greening to reduce the risk of human heat stress. It is also critical to make cities more attractive and enhancing to human well-being to achieve enhancing sustainable urbanization as one of the principal goals for the Nature-based Solutions.

Global Atmospheric Transport and Source-Receptor Relationships for Arsenic.

Arsenic and many of its compounds are toxic pollutants in the global environment. They can be transported long distances in the atmosphere before depositing to the surface, but the global source-receptor relationships between various regions have not yet been assessed. We develop the first global model for atmospheric arsenic to better understand and quantify its intercontinental transport. Our model reproduces the observed arsenic concentrations in surface air over various sites around the world. Arsenic emissions from Asia and South America are found to be the dominant sources for atmospheric arsenic in the Northern and Southern Hemispheres, respectively. Asian emissions are found to contribute 39% and 38% of the total arsenic deposition over the Arctic and Northern America, respectively. Another 14% of the arsenic deposition to the Arctic region is attributed to European emissions. Our results indicate that the reduction of anthropogenic arsenic emissions in Asia and South America can significantly reduce arsenic pollution not only locally but also globally.

Reduction of Solar UV Radiation Due to Urban High-Rise Buildings--A Coupled Modelling Study.

Solar UV radiation has both adverse and beneficial effects to human health. Using models (a radiative transfer model coupled to a building shading model), together with satellite and surface measurements, we studied the un-obstructed and obstructed UV environments in a sub-tropical urban environment featured with relatively high pollution (aerosol) loadings and high-rise buildings. Seasonal patterns of the erythemal UV exposure rates were governed by solar zenith angles, seasonal variations of aerosol loadings and cloud effects. The radiative transfer modelling results agreed with measurements of erythemal UV exposure rates and spectral irradiances in UVA and UVB ranges. High-rise buildings and narrow road width (height to width, H/W, ratios up to 15) reduced the modelled total UV (UVA+UVB) radiation and leave 10% of the un-obstructed exposure rate at ground-level at noon. No more than 80% of the un-obstructed exposure rate was received in the open area surrounded by 20-storey buildings. Our modelled reduction of UVB radiation in the urban environment was consistent with similar measurements obtained for Australia. However, our results in more extreme environments (higher H/W ratios) were for the first time reported, with 18% of the un-obstructed exposure rate remained at the ground-level center of the street canyon.

Trans-oceanic transport of 137Cs from the Fukushima nuclear accident and impact of hypothetical Fukushima-like events of future nuclear plants in Southern China.

A Lagrangian model was adopted to assess the potential impact of (137)Cs released from hypothetical Fukushima-like accidents occurring on three potential nuclear power plant sites in Southern China in the near future (planned within 10 years) in four different seasons. The maximum surface (0-500 m) (137)Cs air concentrations would be reached 10 Bq m(-3) near the source, comparable to the Fukushima case. In January, Southeast Asian countries would be mostly affected by the radioactive plume due to the effects of winter monsoon. In April, the impact would be mainly on Southern and Northern China. Debris of radioactive plume (~1 mBq m(-3)) would carry out long-range transport to North America. The area of influence would be the smallest in July due to the frequent and intense wet removal events by trough of low pressure and tropical cyclone. The maximum worst-case areas of influence were 2382000, 2327000, 517000 and 1395000 km(2) in January, April, July and October, respectively. Prior to the above calculations, the model was employed to simulate the trans-oceanic transport of (137)Cs from the Fukushima nuclear accident. Observed and modeled (137)Cs concentrations were comparable. Sensitivity runs were performed to optimize the wet scavenging parameterization. The adoption of higher-resolution (1° × 1°) meteorological fields improved the prediction. The computed large-scale plume transport pattern over the Pacific Ocean was compared with that reported in the literature.

Origin and distribution of trace elements in high-elevation precipitation in southern China.

INTRODUCTION: During a 2009 investigation of the transport and deposition of trace elements in southern China, 37 event-based precipitation samples were collected at an observatory on Mount Heng, China (1,269 m asl). METHODS: Concentrations of trace elements were analyzed using inductively coupled plasma-mass spectrometry and the wet deposition fluxes were established. A combination of techniques including enrichment factor analysis, principal component analysis, and back trajectory models were used to identify pollutant sources. RESULTS: Trace element concentrations at Mount Heng were among the highest with respect to measured values reported elsewhere. All elements were of non-marine origin. The elements Pb, As, Cu, Se, and Cd were anthropogenic, while Fe, Cr, V, Ba, Mn, and Ni were of mixed crustal/anthropogenic origin. The crustal and anthropogenic contributions of trace elements were 12.8 % (0.9 ~ 17.4 %) and 87.2 % (82.6 ~ 99.1 %), with the maximum crustal fraction being 17.4 % for Fe. Coal combustion, soil and road dust, metallurgical processes, and industrial activities contributed to the element composition. CONCLUSIONS: Summit precipitation events were primarily distant in origin. Medium- to long-range transport of trace elements from the Yangtze River Delta and northern China played an important role in wet deposition at Mount Heng, while air masses from south or southeast of the station were generally low in trace element concentrations.

Evaluation of trace elements contamination in cloud/fog water at an elevated mountain site in Northern China.

Totally 117 cloud/fog water samples were collected at the summit of Mt. Tai (1534m a.s.l.)-the highest mountain in the Northern China Plain. The results were investigated by a combination of techniques including back trajectory model, regional air quality and dust storm models, satellite observations and Principal Component Analysis. Elemental concentrations were determined by Inductively Coupled Plasma Mass Spectrometry, with stringent quality control measures. Higher elemental concentrations were found at Mt. Tai compared with those reported by other overseas studies. The larger proportions and higher concentrations of toxic elements such as Pb and As in cloud/fog water compared with those in rainwater at Mt. Tai suggests higher potential hazards of cloud/fog water as a source of contamination in polluted areas to the ecosystem. Peak concentrations of trace elements were frequently observed during the onset of cloud/fog events when liquid water contents of cloud/fog water were usually low and large amount of pollutants were accumulated in the ambient air. Inverse relationship between elemental concentrations and liquid water contents were only found in the samples with high electrical conductivities and liquid water contents lower than 0.3gm(-3). Affected mainly by the emissions of steel industries and mining activities, air masses transported from south/southwest of Mt. Tai were frequently associated with higher elemental concentrations. The element Mn is attributed to play an important role in the acidity of cloud/fog water. The composition of cloud/fog water influenced by an Asian dust storm event was reported, which was seldom found in the literature.

Observational and modeling study of dry deposition on surrogate surfaces in a South China city: implication of removal of atmospheric crustal particles.

Dry deposition samples collected during 1999-2001 at a South China site using surrogate surfaces were analyzed by capillary electrophoresis. Collector surface properties played important roles to the dry deposition. The deposition velocities for various species ranged from 0.02 to 1.69 cm s(-1), in general agreement with literature values. More than 90% of Ca(2+) was deposited by sedimentation and its comparable values of dry or wet removal residence times imply that dry deposition is an important atmospheric removal process for the ubiquitous crustal species in South China, compared with precipitation scavenging. Relatively good agreement was found when the species deposition velocities were modeled based on up-to-date knowledge of particle dry deposition. The total depositions for anthropogenic and crustal species in northern China are likely to be much higher than those in the south, including our site where the fluxes of the acidic species SO(4)(2-) and NO(3)(-) were 4.4 and 2.2 g m(-2) year(-1), respectively. The sum of dry deposition for cations Na(+), Ca(2+), Mg(2+), and K(+) contributes 44% of the total flux, which is equivalent to the value estimated in Europe.

Monitoring long-term variation of aerosol composition: a dual particle-size approach applied to Hong Kong.

The 1990's time series in Hong Kong for various components of total suspended particulate matter (TSP) and PM10 have been analyzed in order to assess two distinct types of anthropogenic input. The first of these relates to the immense reclamation and construction activities for new developments and airport construction. The concentrations of crustal components in PM > 10 (= TSP - PM10) were found to peak at the time of this maximum activity. A second type of anthropogenic input, ambient lead from petrol vehicles, has decreased in Hong Kong and now represents a regional background. Ambient bromine now arises mainly from the seasalt source.