Integrated modelling of climate control and air pollution: Methodology and results from one-way coupling of an energy–environment–economy (E3MG) and atmospheric chemistry model (p-TOMCAT) in decarbonising scenarios for Mexico to 2050

This paper reports the methodology and results of an one-way coupling of the E3 Model at the Global level (E3MG) model to the global atmospheric chemistry model, p-TOMCAT, to assess the effects on the concentrations of atmospheric gases over Mexico of a low-GHG scenario compared to an alternative reference case with higher use of fossil fuels. The paper covers the data and methods, changes in atmospheric gas concentrations, the macroeconomic effects of the policies, and the outcome for pollution. The results suggest that in the conditions of underemployment in Mexico, substantial investment in low-carbon technologies, such as electric vehicles, heat pumps and geo-thermal power, could improve employment prospects, maintain growth, as well as reduce some of the risks associated with prospective falls in oil revenues. The concentrations of low-level ozone, both for Mexico-only and global decarbonisation scenarios relative to the original reference case, show appreciable reductions, sufficient to bring concentrations close to the WHO guideline levels. An indication is given of the potential scale of the benefits on human health in Mexico City.     

Reassessment of the Ocean-To-Atmosphere Flux of Carbon Monoxide

Abstract

Carbon monoxide (CO) in the surface sea waters is produced predominantly by photochemical processes, oxidized by micro-organisms and outgassed to the atmosphere. to assess carbon monoxide flux from the oceans to the atmosphere, the photochemical production and microbial oxidation of carbon monoxide in the oceanic mixed-layer was investigated during several oeanographic cruises and in the laboratory. the photoproduction rate of carbon monoxide was found to be well correlated to the concentration of dissolved organic carbon (DOC) in coastal and open ocean surface waters. Taking a global average carbon monoxide production rate of 10 ± 2 nmole litre^?1 (mg DOC hr)^?1 in the surface open ocean water, and 25 ± 7 nmole litre^?1 (mg DOC hr)^?1 in coastal sea water, at cloud-free summer solar noon, the photochemical production of carbon monoxide in the global oceans is estimated to be at a rate of 1200 ± 200 Tg CO y^?1. the microbial carbon monoxide turnover time in the mixed-layer was observed to range from hours in a coastal estuary to 16 days in the Pacific along 1057deg; W in dark incubations. Natural sunlight can largely inhibit the microbial consumption of carbon monoxide in surface water. On a global scale, microbial consumption is responsible for the loss of less than 10% of photochemical produced carbon monoxide in the surface ocean. Field measurements have shown that the net transport of carbon monoxide from the euphotic zone to the underlying deeper ocean water is limited and that the overall life time in surface sea waters is less than 3-4 hours. When combined, these field measurements with the photoproduction and microbial consumption rates obtained, we estimate the oceanic flux to the atmosphere is about 1000 ± 200 Tg CO y^?1, which represents the largest single source of atmospheric carbon monoxide.     

Influence of soil pH and application rate on the oxidation of calcium sulfite derived from flue gas desulfurization

Calcium sulfite hemihydrate (CaSO(3).0.5H2O), a common byproduct of coal-fired utilities, is fairly insoluble and can decompose to release toxic SO2 under highly acidic soil conditions; however, it can also oxidize to form gypsum. The objective of this study was to examine the effects of application rate and soil pH on the oxidation of calcium sulfite under laboratory conditions. Oxidation rates measured by release of SO4-S to solution decreased with increasing application rate. Leachate SO4-S from soils amended with 1.0 to 3.0 g kg-1 CaSO3 increased over a 21 to 28 d period before reaching a plateau. At 4 g kg-1, maximum SO4-S release was delayed until Week 7. Oxidation and release of SO4-S from soil amended with 3.0 g kg-1 calcium sulfite increased markedly with decreasing soil pH. After only 3 d incubation, the concentrations of SO4-S in aqueous leachates were 77, 122, 170, 220, and 229 mg L-1 for initial soil pH values of 7.8, 6.5, 5.5, 5.1, and 4.0, respectively. At an initial soil pH value of 4.0, oxidation/dissolution did not increase much after 3 d. At higher pH values, oxidation was maximized after 21 d. These results suggest that autumn surface applications of calcium sulfite in no-till systems should permit ample time for oxidation/dissolution reactions to occur without introducing biocidal effects related to oxygen scavenging. Soil and annual crops can thus benefit from additions of soluble Ca and SO4 if calcium sulfite is applied in advance of spring planting.     

Air-sea gas exchange of HCHs and PCBs and enantiomers of alpha-HCH in the Kattegat Sea region

Concentrations and air-water gas exchange of polychlorinated biphenyls (PCBs) and hexachlorocyclohexanes (HCHs) were determined in nine paired air and water samples. The samples were collected monthly in the Kattegat Sea between December 1998 and November 1999. Average fugacity and flux values indicated that PCBs were oversaturated in the water, while HCHs were net deposited. Variations were large over the year, especially during spring and summer. Air parcel back trajectories suggested that air concentrations over the Kattegat Sea are largely dependent of air mass origin. Seasonal trends were detected for airborne HCHs and for PCBs in water. The air and water enantiomeric compositions of alpha-HCH indicated that a larger portion of alpha-HCH in air originated from the underlying water during summer than during winter.     

Polychlorinated dibenzo-p-dioxins (PCDDs) and furans (PCDFs) in urban air and deposition in the United Kingdom

Polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) have been monitored in air and deposition at four UK urban sites (London, Cardiff, Manchester and Stevenage) since the beginning of 1991; data from the first 2 years are presented here. Median Σ2,3,7,8-substituted PCDD/F concentrations in air were 3.2, 4.0, 3.5 and 2.6 pg/m³ respectively for London, Cardiff, Manchester and Stevenage. Median Σ2,3,7,8-substituted PCDD/F deposition fluxes were 1.5 ng/m²/day in London, 1.4 ng/m²/day in Cardiff and Manchester and 0.79 ng/m²/day in Stevenage. Seasonal variations in the PCDD/F concentrations were observed at all sites for both air and deposition, with concentrations/fluxes generally elevated during the winter.     

Observations on long-term air-soil exchange of organic contaminants

Evidence for long-term changes in the soil composition of selected organic compounds, brought about by exchanges with the atmosphere, is briefly reviewed. In the case of some compounds — such as benzo(a)pyrene and octachlorodibenzo-p-dioxin, soils may be significant long-term environmental sinks for atmospherically-derived material. In other cases — such as phenanthrene and some of the lighter PCBs, de-gassing or volatilisation from soil back to the air can occur under certain conditions. Hence the soil may act as a “short-term” sink, and a potential source to atmosphere. Indeed, for some ‘semi-volatile’ compounds used in large quantities in the past — such as PCBs, soil outgassing may actually be an extremely important source to contemporary air. Furthermore, soil outgassing from areas of former high use may provide an important driving mechanism for continued “global cycling” of a range of semi-volatile organochlorine compounds.     

Kinetic evaluation of H2S and NH3 biofiltration for two media used for wastewater lift station emissions

In this study, biofiltration using a natural wood chip medium and a commercial biofiltration medium was evaluated for the removal of moderate concentrations of hydrogen sulfide (H2S) (up to 100 parts per million by volume [ppmv]) in the presence of significant concentrations of ammonia (NH3). These levels were chosen as representative of wastewater lift station emissions in the Brownsville, TX, area. NH3-removing portions of the biofilms may compete with H2S-removing portions and inhibit H2S removal. H2S process removal efficiencies for the commercial and natural media ranged from 90 to 96% depending on inlet loading and media type and bed height. Kinetic analysis of the H2S removal process followed apparent first-order reaction behavior. The average first-order reaction rates were 0.03 sec(-1) for the commercial medium and 0.09 sec(-1) for the natural medium. Pressure drops across the columns ranged from 0.41 in. H2O/ft for the commercial medium to 1.41 in. H2O/ft for the natural medium. NH3 gas levels of up to 80 ppmv did not affect the H2S removal process efficiency, and calculated kinetic rate constants for H2S removal remained almost the same. The NH3 gas also was removed simultaneously with the H2S up to 98% removal efficiency by the commercial medium.     

Environmental fate and bioavailability of agent orange and its associated dioxin during the vietnam war

BACKGROUND: In 1996, the Committee on the Assessment of Wartime Exposure to Herbicides in Vietnam of the National Academy of Sciences' Institute of Medicine (IOM) issued a report on an exposure model for use in epidemiological studies of Vietnam veterans. This exposure model would consider troop locations based on military records; aerial spray mission data; estimated ground spraying activity; estimated exposure opportunity factors; military indications for herbicide use; and considerations of the composition and environmental fate of herbicides, including changes in the TCDD content of the herbicides over time, the persistence of TCDD and herbicides in the environment, and the degree of likely penetration of the herbicides into the ground. When the final report of the IOM Committee was released in October 2003, several components of the exposure model envisioned by the Committee were not addressed. These components included the environmental fate of the herbicides, including changes in the TCDD content over time, the persistence of TCDD and herbicides in the environment, and the degree of likely penetration of herbicides into the ground. This paper is intended to help investigators understand better the fate and transport of herbicides and TCDD from spray missions, particularly in performing epidemiological studies. METHODS: This paper reviews the published scientific literature related to the environmental fate of Agent Orange and the contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and discusses how this affected the potential exposure to TCDD of ground troops in Vietnam. Specifically, the mechanisms of dissipation and degradation as they relate to environmental distribution and bioavailability are addressed. RESULTS: The evaluation of the spray systems used to disseminate herbicides in Vietnam showed that they were capable of highly precise applications both in terms of concentrations sprayed and area treated. Research on tropical forest canopies with leaf area indices (a measure of foliage density) from 2 to 5 indicated that the amount of herbicide and associated TCDD reaching the forest floor would have been between 1 and 6% of the total aerial spray. Studies of the properties of plant surface waxes of the cuticle layer suggested that Agent Orange, including the TCDD, would have dried (i.e., be absorbed into the wax layer of the plant cuticle) upon spraying within minutes and could not be physically dislodged. Studies of Agent Orange and the associated TCDD on both leaf and soil surface have demonstrated that photolysis by sunlight would have rapidly decreased the concentration of TCDD, and this process continued in shade. Studies of 'dislodgeable foliar residues' (DFR, the fraction of a substance that is available for cutaneous uptake from the plant leaves) showed that only 8% of the DFR was present 1 hr after application. This dropped to 1% of the total 24 hrs after application. Studies with human volunteers confirmed that after 2 hrs of saturated contact with bare skin, only 0.15-0.46% of 2,4,5-T, one of the phenoxy acetic acid compounds that was an active ingredient of Agent Orange, entered the body and was eliminated in the urine. CONCLUSIONS: The prospect of exposure to TCDD from Agent Orange in ground troops in Vietnam seems unlikely in light of the environmental dissipation of TCDD, little bioavailability, and the properties of the herbicides and circumstances of application that occurred. Photochemical degradation of TCDD and limited bioavailability of any residual TCDD present in soil or on vegetation suggest that dioxin concentrations in ground troops who served in Vietnam would have been small and indistinguishable from background levels even if they had been in recently treated areas. Laboratory and field data reported in the literature provide compelling evidence on the fate and dislodgeability of herbicide and TCDD in the environment. This evidence of the environmental fate and poor bioavailability of TCDD from Agent Orange is consistent with the observation of little or no exposure in the veterans who served in Vietnam. Appreciable accumulation of TCDD in veterans would have required repeated long-term direct skin contact of the type experienced by United States (US) Air Force RANCH HAND and US Army Chemical Corps personnel who handled or otherwise had direct contact with liquid herbicide, not from incidental exposure under field conditions where Agent Orange had been sprayed.