A 2-D model of global aerosol transport

The distribution of aerosol particles in the troposphere is described. Starting with long term mean seasonal flow and diffusivities as well as temperature, cloud distribution (six cloud classes), relative humidity and OH radical concentration, the steady state concentration of aerosol particles and SO₂ are calculated in a two-dimensional global (height and latitude) model. The following sources and sinks for particles are handled: direct emission, gas-to-particle conversion from SO₂, coagulation, rainout, washout, gravitational settling, and dry deposition. The sinks considered for sulphur emissions are dry deposition, washout, rainout, gasphase oxidation, and aqueous phase oxidation. Model tests with the water vapour cycle show a good agreement between measured and calculated zonal mean precipitation distribution.The steady state concentration distribution for natural emissions reached after 10 weeks model time, may be described by a mean exponent α = 3.2 near the surface assuming a modified Junge distribution and an increased value, α = 3.7, for the combined natural and man-made emission. The maximum ground level concentrations are 2000 and 10,000 particles cm⁻³ for natural and natural plus man-made emissions, respectively. The resulting distribution of sulphur dioxide agrees satisfactorily with measurements given by several authors.     

An alternate pseudospectral model for pollutant transport,diffusion and deposition in the atmosphere

A numerical model of atmospheric transport, diffusion and deposition has been developed for pollutants which are emitted into atmospheric boundary layer with upper boundary condition at the inversion layer and lower boundary condition at the surface. The numerical schemes used in the model are derived from the use of finite Fourier transform. However, instead of using FFT, alternate pseudospectral schemes for evaluations of space derivative terms in the model equation with the settling velocity are presented.The model involves the evaluation of a polynomial function for non-periodic boundary conditions in order to apply the alternate pseudospectral schemes to the periodic function. The numerical results were discussed for different profiles of vertical eddy diffusivity and for different absorptive deposition conditions at the ground.     

Absence of tetraalkyl lead vapors in the atmosphere of Beijing,China

The concentrations of five gaseous methyl and ethyl tetraalkyl lead compounds in urban and rural Beijing during August 1980 have been found to be below a detection limit of 0.1 ng Pb m⁻³. Analyses of six samples of Chinese gasoline indicate no-lead to low-lead composition. These results set a new upper limit to tetraalkyl lead vapor concentrations in a terrestrial environment having little automotive lead emission. They also call into question the recently claimed significance of natural sources for some of the organic lead vapors found in polluted areas of Europe and North America.     

A preliminary analysis of the inhalable particulate lead in the ambient atmosphere of the city of Riyadh,Saudi Arabia

The inhalable particles in the ambient atmosphere in the city of Riyadh have been sampled during the working day (7 a.m.–4 p.m.) over the test period. Samples were taken every 3 h using an Automatic Dichotomous Sampler placed in the College of Engineering, King Saud University at a height of 25 m above the ground. A weather station 3 m above the sampler was used to record (simultaneously) the meteorological data. These data were used to determine the wind rose and the hourly standard deviation of the horizontal wind direction, which, in turn, gives the hourly atmospheric stability class.The particulates in each size range: coarse (2.5–15 μm) and fine (〈 2.5 μm) were analyzed using an Atomic Absorption Unit to determine the lead content in each sample.The results were then used to determine the directional fluxes of fine and coarse lead particulates. It has been shown that the average concentration of lead during the working day is about twice the international standards. The concentration decreases during the weekends (Thursday and Friday) due to the reduction in traffic loads, and decreases to a minimum on Fridays when most of industrial activities are stopped. More than 70% of the lead fluxes passed by the sampler are associated with wind from E to S which is the direction of the city center and the industrial site of Riyadh.     

A numerical model of pollutant transport

A mathematical model of urban air pollution is described in which the pollutant is represented by fluid particles. The particles move randomly to simulate the effect of atmospheric turbulence and are also advected on the mean wind field. The concentration of pollutant at any point is given by the local density of particles. This approach provides great generality and flexibility for handling complex and time-varying emissions and atmospheric conditions. The model has been applied to sulphur dioxide in Melbourne.     

嘉兴市大气污染特征及区域传输影响研究

对嘉兴市2013—2017年的大气污染特征进行了分析,同时研究了区域传输对其PM_(2.5)、PM_(10)、NO_2和SO_2的影响和嘉兴市O_3生成的主要原因。结果表明,自2013年以来嘉兴市PM2.5逐年下降,重度污染及以上天数逐年减少,环境空气质量总体呈逐年好转趋势。截至2017年,PM_(10)、NO_2、SO_2和CO均已达到《环境空气质量标准》(GB 3095—2012)二级标准,但PM_(2.5)和O_3仍未达标。2017年,周边地区(苏州市、湖州市、上海市、杭州市、绍兴市和宁波市)对嘉兴市PM_(2.5)、PM_(10)、NO_2和SO_2的传输贡献分别为36.2%、31.9%、25.6%、26.7%,季节差异较大,建议根据区域传输的季节性变化,制定针对性的联防联控措施。嘉兴市O3污染主要受挥发性有机物(VOCs)控制,应重点控制VOCs排放,辅以控制NO_x排放。     

Colloid-facilitated transport of lead in natural discrete fractures

Colloid-facilitated transport of lead (Pb) was explored in a natural chalk fracture with an average equivalent hydraulic aperture of 139 μm. Tracer solution was prepared by adding montmorillonite (100 mg L^?1) and/or humic acid (HA) (10 mg L^?1) to modified artificial rainwater containing dissolved Pb (21.4 mg Pb L^?1), naturally precipitated PbCO₃ particles (16.4 mg Pb L^?1) and LiBr (39.0 mg L^?1). We found that Pb is only mobile when associated with colloids. PbCO₃ particles were not mobile in the fracture. The addition of HA to the montmorillonite suspension increased the suspension's mobility and therefore promoted the colloid-facilitated transport of Pb. The increases in pH and sodium absorption ratio induced by the chalk-tracer solution interactions appeared to increase the dispersion and mobilization of colloids entering the fracture. The dominant colloid-facilitated transport of Pb reported in this study has significant implications for risk assessment of Pb mobility in fractured rocks.     

Issues in evaluating the long-term global impacts of transport policy

This paper provides an overview of issues involved in evaluating the long-term impacts of transport policy. It considers the effects of global warming, and the costs and benefits of action to reduce emissions of greenhouse gases. The overall case for such action rests on the choice of discount rate. The paper considers the relative effectiveness of taxes and regulations in controlling emissions from the transport sector, and contrasts direct action on road traffic with indirect action via policies to increase travel on public transport. After a brief mention of the issue of biodiversity, the paper concludes with some reflections on the political acceptability of different policies.     

Economic instruments, transport and the global environment

The use of economic instruments, such as charges, in abating climate change is assessed, with special reference to their application in the transport sector. The general strategies and instruments for global environmental policies are presented. The role of economic instruments in this context is highlighted, both in terms of theory and of application. Economic instruments are then analysed from the perspective of transport policies. Climate and transport appear to have different perspectives on economic instruments. The analysis leads to a framework for developing climate-related economic instruments in transport. These may result in substantial economic savings, especially if approached internationally and if distributional and institutional problems can be overcome. The integration of climate concerns into transport policies can be improved, and several suggestions are made in this respect.     

Ubiquity of bisphenol A in the atmosphere

Bisphenol A (BPA) is a suspected endocrine disruptor in the environment. However, little is known about its distribution and transport in the atmosphere. Here, the concentrations of BPA in the atmospheric aerosols from urban, rural, marine, and the polar regions were measured using solvent extraction/derivatization and gas chromatography/mass spectrometry technique. The concentrations of BPA (1-17,400 pg m⁻³) ranged over 4 orders of magnitude in the world with a declining trend from the continent (except for the Antarctica) to remote sites. A positive correlation was found between BPA and 1,3,5-triphenylbenzene, a tracer for plastic burning, in urban regions, indicating that the open burning of plastics in domestic waste should be a significant emission source of atmospheric BPA. Our results suggest that the ubiquity of BPA in the atmosphere may raise a requirement for the evaluation of health effects of BPA in order to control its emission sources, for example, from plastic burning.     

The distribution of the chlorinated solvents dichloromethane,perchloroethylene, and trichloroethylene in the global atmosphere

Dichloromethane, perchloroethylene, and trichloroethylene are commercially important chlorinated solvents whose health and environmental impacts are under scrutiny in the industrial world. Their distributions in the global atmosphere have been computed based on data from the Reactive Chlorine Emissions Inventory (RCEI) project using the Global Balance Environment (GLOBE) model, a 3-D radiative-dynamical-chemical model. Their atmospheric lifetimes, scaled to an observed methyl chloroform lifetime of 4.8 years, are 158 days, 105 days, and 4.3 days, respectively. They have strong interhemispheric gradients, with maximum zonal mean surface concentrations in the winter mid-latitude northern hemisphere of approximately 40 ppt, 9 ppt, and 2.5 ppt, respectively. Their spatial distributions show significant seasonal variability, and are sensitive to vertical mixing by cumulus convection and horizontal mixing by synoptic-scale turbulence. While the model interhemispheric exchange time (1.0 years) and computed atmospheric lifetimes are very sensitive to sub-grid scale diffusion, interhemispheric gradients of the chlorinated solvents are not. The simulated results suggest a greater importance for oceanic emissions of perchloroethylene and trichloroethylene than has previously been assumed.     

Transport impacts on atmosphere and climate: Land transport

Emissions from land transport, and from road transport in particular, have significant impacts on the atmosphere and on climate change. This assessment gives an overview of past, present and future emissions from land transport, of their impacts on the atmospheric composition and air quality, on human health and climate change and on options for mitigation.In the past vehicle exhaust emission control has successfully reduced emissions of nitrogen oxides, carbon monoxide, volatile organic compounds and particulate matter. This contributed to improved air quality and reduced health impacts in industrialised countries. In developing countries however, pollutant emissions have been growing strongly, adversely affecting many populations. In addition, ozone and particulate matter change the radiative balance and hence contribute to global warming on shorter time scales. Latest knowledge on the magnitude of land transport's impact on global warming is reviewed here.In the future, road transport's emissions of these pollutants are expected to stagnate and then decrease globally. This will then help to improve the air quality notably in developing countries. On the contrary, emissions of carbon dioxide and of halocarbons from mobile air conditioners have been globally increasing and are further expected to grow. Consequently, road transport's impact on climate is gaining in importance. The expected efficiency improvements of vehicles and the introduction of biofuels will not be sufficient to offset the expected strong growth in both, passenger and freight transportation. Technical measures could offer a significant reduction potential, but strong interventions would be needed as markets do not initiate the necessary changes. Further reductions would need a resolute expansion of low-carbon fuels, a tripling of vehicle fuel efficiency and a stagnation in absolute transport volumes. Land transport will remain a key sector in climate change mitigation during the next decades.     

A review on reactive transport model and porosity evolution in the porous media

Environmental Science and Pollution Research - This work comprehensively reviews the equations governing multicomponent flow and reactive transport in porous media on the pore-scale, mesoscale and...     

Hydrogen sulfide in the atmosphere of the northern equatorial Atlantic Ocean and its relation to the global sulfur cycle

Concentrations of hydrogen sulfide were measured in remote marine atmospheres of tropical and sub-tropical regions. The gas was collected on filters impregnated with silver nitrate and analyzed fluorometrically. Average measured background concentrations ranged from 5 to 50 pptr (1 part in 10¹² parts of the air) by volume. These concentrations are between four and forty times lower than previously accepted values and indicate that the atmospheric lifetime of hydrogen sulfide may be as short as a few hours. The results generally support current estimates of the extent of hydrogen sulfide production by the oceans. Nonetheless, it is concluded that more precise estimates of atmospheric residence times are required before firm estimates of production rates can be made.     

An observation-based model for analyzing ozone precursor relationships in the urban atmosphere

An Observation-Based Model (OBM) is described, which uses in-situ atmospheric observations to determine the sensitivity of ozone concentrations in an urban atmosphere to changes in the emissions of ozone precursors (i.e., volatile organic compounds and nitrogen oxides). The model is formulated following the concept of Relative Incremental Reactivity (RIR) developed by Carter and Atkinson. In the OBM, however, observed concentrations rather than emission inventories are used to drive the photochemical simulations and thereby ensure that the calculations are carried out for the proper mix of nitrogen oxides and volatile organic compounds. From these calculations, a series of sensitivity factors, or RIRs, are inferred that can be used to (1) determine whether reducing emissions of nitrogen oxide or emissions of hydrocarbons would be most effective in abating ozone in a given urban area, and (2) identify the most critical subset of hydrocarbons present in an urban atmosphere causing ozone exceedances. Because the OBM is relatively easy and inexpensive to operate and makes use of data that are increasingly available, it can be used to analyze a wide array of ozone episodes and, thus, could prove to be a relatively cost-effective tool for the analysis of ozone precursor relationships in an urban atmosphere. On the other hand, because the OBM is diagnostic rather than prognostic, it cannot be used in a predictive mode to estimate exactly how much emission reduction is needed to reduce ozone concentrations. For this reason, the OBM should be viewed as a complement to, rather than a substitute for, more sophisticated gridded, emission-based models. To illustrate the characteristics of the OBM and to demonstrate its applicability, we first compare the results of the OBM to those obtained from a series of simulations of the Atlanta metropolitan area using the Urban Airshed Model (UAM), a three-dimensional Eulerian grid model. The OBM is then used to analyze a dataset obtained from the 1990 Atlanta Ozone Study, an EPA field sampling program conducted during the summer of 1990. Because of limitations and potential flaws in the 1990 Atlanta dataset, the results of this OBM analysis are largely illustrative rather than definitive. Nevertheless, a few important issues are elucidated by the analysis. These include (1) the importance of accounting for biogenic hydrocarbons produced from urban vegetation; (2) the potential flaw in using early-morning VOC-to-NOx ratios to infer whether ozone production is limited by VOC or NOx; (3) the critical need for high-sensitivity nitrogen oxide measurements to quantify the sub-ppbv concentrations of NO during the afternoon hours; and (4) the need to consider a number of individual ozone episodes in studying an urban atmosphere because of the possibility that the degree of VOC- and NOx-limitation may vary from one episode to another.