Atmospheric Chemistry of Toxic Contaminants 1. Reaction Rates and Atmospheric Persistence

Using structure-reactivity relationships between reaction rate constants and ionlzatlon potentials for structural homologues, estimates are presented for the rate constants of the reactions of ozone, the hydroxyl radical, and the nitrate radical with forty toxic air contaminants for which no or little data are available. These rate constants are in turn used to estimate the atmospheric persistence of saturated allphatics, unsaturated allphatics, and aromatic toxic organics. The corresponding atmospheric half-lives for removal by chemical reactions range from a few hours for the most reactive toxics (chloroprene, hexachlorocyclo-pentadiene, cresols, nitrosamines, maleic anhydride) to several months for the least reactive compounds (nitrobenzene, methyl bromide, phosgene).     

Population Exposure to Toxic Substances: Use of 1970 Census Data

A particulate sampling train has been constructed which satisfies the conflicting requirements of isokinetic sample extraction and constant flow rate through an inertial sizing device. Its design allows a variable fraction of the filtered emission gas to be added to the sample upstream of the inertial sizing device in order to maintain a preselected flow rate through this device while the gas flow rate into the sampling nozzle is adjusted to remain isokinetic with the local duct velocity. The prototype emission gas recycle (EGR) train was constructed by relatively simple modifications of a commercially available Method 5 sampling system, and much of the sampling technique is identical with Method 5 protocol. The train was tested by comparison of parallel runs in the EPA/SRI wind tunnel using redispersed fly ash. In one series of runs performed without inertial sizing devices, the EGR train and a colocated non- EGR train sampled 3-point traverses. The differences of the average mass concentrations measured by the two trains was 3.3 percent, with a standard deviation of 4.7 percent. In the next series of runs, identical cyclone inertial sizing devices were added to each train. The difference of the average mass concentration for these runs was 1.2 percent, with a standard deviation of 5.7 percent.     

Atmospheric Chemistry of Toxic Contaminants. 6. Nitrosamines: Dialkyl Nitrosamines and Nitrosomorpholine

Detailed mechanisms are outlined for the reactions that contribute to in-sltu formation and atmospheric removal of dlmethylnitrosamine, diethylnitrosamlne, methyl-ethylnltrosamine, and nitrosomorphollne. In-sltu formation involves the rapid reaction of amines with the hydroxyl radical, leading to nltrosamlnes, nltramlnes, amides, and aldehydes. Nitrosamlne photolysis accounts for their rapid daytime removal, leading to amlno radicals whose atmospheric reactions are also discussed.     

Atmospheric Chemistry of Toxic Contaminants. 3. Unsaturated Aliphatics: Acrolein,Acrylonitrile, Maleic Anhydride

Detailed mechanisms are outlined for the chemical reactions that contribute to In-situ formation and atmospheric removal of the unsaturated aliphatic contaminants acrolein, acrylonitrile, and maleic anhydride. In-situ formation of small amounts of acrolein and maleic anhydride may Involve the reaction of OH (and O₃) with 1,3-dienes and the reaction of OH with aromatic hydrocarbons, respectively. There is no known pathway for In-situ formation of acrylonitrile. Rapid removal of acrolein (half-life = less than one day) and of maleic anhydride (half-life = several hours) is expected from their rapid reactions with OH (major), O₃, and NO₃. These reactions lead to formaldehyde and glyoxal from acrolein and to dicarbonyls from maleic anhydride. Acrylonitrile is removed at a slower rate (half-life = 2–7 days) by reaction with OH, leading to formaldehyde and formyl cyanide.     

确定大气环境标准方法的探讨

对使用或生产我国尚无环境控制标准污染物质的企业如何管理．经对有关法规、资料的研究，推荐采用确定环境控制标准的方法，以控制这些污染物质的排放及其对环境的影响。     

Atmospheric Chemistry of Toxic Contaminants. 5. Unsaturated Halogenated Aliphatics: Allyl Chloride,Chloroprene, Hexachlorocyclopentadiene,Vinylidene Chloride

Detailed mechanisms are outlined for the chemical reactions involved In the atmospheric removal of four unsaturated chlorinated aliphatic contaminants, allyl chloride, chloroprene, hexachlorocyclopentadiene and vlnylldene chloride. Rate constants estimated from structure-reactivity relationships Indicate rapid removal for all four compounds by reactions with OH (major), ozone, and NO₃, with half-lives of 2-16 hrs for removal by reaction with OH. Reaction products of allyl chloride (formaldehyde, chloroacetaldehyde, peroxychloroacetyl nitrate) and vinylidene chloride (formaldehyde, phosgene, chloroacetyl chloride) are consistent with OH addition-Initiated pathways that include Cl atom elimination. The chlorine atoms produced In the OH reaction sequence react rapidly with all four unsaturated compounds, but these reactions are of negligible Importance for atmospheric removal of the four toxic contaminants studied. Analogous mechanisms are discussed for chloroprene (leading to formaldehyde, CH₂ = CCICHO, and CICOCHO) and for hexachlorocyclopentadlene (leading to oxalyl chloride and CICOCCI₂COCI).     

Atmospheric Chemistry of Toxic Contaminants. 2. Saturated Aliphatics: Acetaldehyde,Dioxane, Ethylene Glycol Ethers,Propylene Oxide

Detailed mechanisms are outlined for the chemical reactions that contribute to In-situ formation and atmospheric removal of the saturated aliphatic contaminants acetaldehyde, dioxane, ethylene glycol ethers (methyl, ethyl, n-butyl) and propylene oxide. In-situ formation Is of major Importance for acetaldehyde. In-situ removal Involves reaction with OH (all compounds) and, for acetaldehyde, photolysis and reaction with NO3. Acetaldehyde, dioxane, and the ethers are rapidly removed (half-lives of less than one day), leading to PAN (acetaldehyde) and to 2-oxodioxane and formaldehyde (dioxane). Reaction products of the glycol ethers include a large number of hydroxyesters, hydroxyacids, and hydroxycarbonyls. Propylene oxide reacts only slowly with OH, with an atmospheric half-life of 3-10 days, to yield formaldehyde, acetaldehyde, and PAN. Uncertainties in the reaction mechanisms for dioxane, the glycol ethers, and propylene oxide are discussed and include C-C vs C-0 bond scission in alkoxy radicals as well as alkoxy radical unimolecular decomposition vs reaction with oxygen.     

Atmospheric turbidity in Kuwait

The paper discusses the effect or atmospheric constituents on the depletion or beam radiation in Kuwait with particular emphasis on the effect or aerosol particles. It is shown that atmospheric turbidity is particularly large during June and July as compared to other months of the year. It is also shown that for a good part of the year the effect of aerosol particles on beam radiation attenuation is equivalent to, or larger than, the combined effects of ozone, water vapor and gas molecules.     

Toxic substances in rivers and streams

Many of the toxic substances entering freshwaters today are those which were present several decades ago, but others have become significant recently. The effects of toxicants in flowing waters are modified by unidirectional transport and dispersion which afford the potential for a degree of 'self-purification'. The chemical quality of the receiving water also affects toxicity. Biological factors also contribute to the ultimate effect of pollutants. The potential for accumulation of toxic substances within tissues increases the significance of certain pollutants which may be present in water even though ambient concentrations are very low. The biota of flowing waters may be restored, following catastrophic entry of pollutants, by drift from unaffected regions upstream. The range of potential toxic substances is very extensive and includes inorganic poisons, organic poisons, heavy metals, pesticides and PCBs. Metals, pesticides and PCBs have the greatest potential for bioaccumulation. Few generalisations can be made regarding the effects of toxic substances on the biota. Each species tends to respond to different toxicants in different ways and even at different stages in its life-history. Toxicity tests conducted under controlled laboratory conditions sometimes produce conflicting results: it is not then to be unexpected that field observations should sometimes vary widely. Determinations of toxicity in laboratory tests must be applied with caution to field conditions and it is not wise to extrapolate findings to other species or environments.     

Atmospheric mercury levels in the Slovak Republic.

Total mercury concentrations (as a sum of vapor and particulate mercury) were measured in 24-h samples of ambient air in 20 different localities of the Slovak Republic eight times during the period 1996-1997. Vapor mercury was analyzed on site by atomic fluorescence with amalgamation technique. Particulate mercury was determined by vapor hydride atomic absorption spectrometry after wet digestion of filters with particulate air samples. The results showed that 34% of the 160 individual total mercury concentrations exceeded 5 ng/m3--the ambient air quality guideline value recommended by the WHO. The range of total mercury concentrations in the ambient air of Slovakia was: 1.13-3.98 ng/m3 (geom. mean 2.63) in the background area; 2.25-5.27 ng/m3 (geom. mean 3.64) in the agricultural areas; 1.73-20.53 ng/m3 (geom. mean 4.57) in the urban areas; and 1.53-39.85 ng/m3 (geom. mean 5.28) in the industrial areas. The highest mercury levels occurred in areas with metallurgical industry and coal combustion. The predominant form of mercury present in air was vapor mercury. The particulate fraction of mercury in ambient air (as a percentage of total mercury) varied widely from 0.4% to 42.1% (geom. mean = 4.4%). This fraction was lower in agricultural areas (2.3%) than in urban areas (5.3%). Although the atmospheric vapor mercury concentrations were slightly higher in summer than in winter, a direct correlation of vapor mercury concentrations and ambient air temperature was not found. Furthermore, the particulate mercury concentrations did not correlate with total particulate levels.