Photochemical Ozone Creation Potential Research Articles

Photochemical ozone creation potentials for oxygenated volatile organic compounds: sensitivity to variations in kinetic and mechanistic parameters

The sensitivity of Photochemical Ozone Creation Potentials (POCP) to a series of systematic variations in the rates and products of reactions of radical intermediates and oxygenated products is investigated for the C 4 alcohols, 1-butanol ( n-butanol) and 2-methyl-1-propanol ( i-butanol), using the recently developed Master Chemical Mechanism (MCM) as the base case. The POCP values are determined from the calculated formation of ozone in the boundary layer over a period of approximately five days along an idealised straight line trajectory, using a photochemical trajectory model and methodology described in detail previously. The results allow the relative impacts on calculated ozone formation of various classes of chemical reaction within the degradation chemistry to be assessed. The calculated POCP is found to be very insensitive to many of the changes investigated. However, it is found to be sensitive to variations in the rate coefficient for the initiating reaction with OH ( k OH ), although the sensitivity decreases with increasing k OH . The POCP appears to vary approximately linearly with k OH at low values (i.e. k OH less than ca. 4×10 -13 cm 3 molecule -1 s -1), whereas at high reactivities (i.e. k OH greater than ca. 4×10 -11 cm 3 molecule -1 s -1), the calculated POCP value is comparatively insensitive to the precise value of k OH . The POCP is also very sensitive to mechanistic changes which influence the yields of unreactive oxygenated products (i.e. those with OH reactivities below ca. 10 -12 cm 3 molecule -1 s -1), for example acetone. The propensity of the organic compound to produce organic nitrates (which act as comparatively unreactive reservoirs for free radicals and NO x ) also appears to have a notable influence on the calculated POCP. Recently reported information relevant to the degradation of oxygenated VOCs is then used to update the chemical schemes for the 17 alcohols and glycols, 10 ethers and glycol ethers, and 8 esters included in the MCM, and new schemes are incorporated for dimethoxy methane (CH 3OCH 2OCH 3) and dimethyl carbonate (CH 3OC(O)OCH 3), which are proposed fuel additives. New or updated POCP values are calculated for all 37 oxygenated VOCs and, where applicable, these are compared with the previous POCP values and reported Maximum Incremental Reactivity (MIR) values.

Photochemical ozone creation potentials for organic compounds in northwest Europe calculated with a master chemical mechanism

Master Chemical Mechanism containing over 2400 chemical species and over 7100 chemical reactions is employed here to describe the atmospheric degradation of 120 organic compounds and the associated regional scale ozone and PAN formation under conditions appropriate to the polluted boundary layer over northwest Europe. Photochemical ozone and PAN creation potentials (POCP and PPCP) are derived for each organic compound from their propensities to form ozone and PAN relative to ethylene and propylene, respectively. The robustness of these POCP values to changes in the NO x emission densities across Europe is tested and the values are compared with previous studies. The POCP values are reviewed and rationalised against the background of our current understanding of the intrinsic properties of each organic compound, their atmospheric degradation pathways and other mechanistic data. These POCPs should assist policy-makers in defining realistic and robust pollution control strategies which focus on those organic compounds which contribute most to regional scale ozone formation across northwest Europe.

Atmospheric Chemical Reactivity and Ozone-Forming Potentials of Potential CFC Replacements

The Montreal Protocol will lead to the eventual phase-out of the production of chlorofluorocarbons (CFCs) and other halogenated organic compounds that are implicated in the depletion of stratospheric ozone. Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) have been developed as potential “in-kind” replacement compounds. To ensure that these compounds are acceptable, industry and regulatory agencies are assessing the safety, toxicology, and environmental impact of the HCFCs and HFCs before widespread production is commenced. One of the environmental issues concerns the contribution that the HCFCs and HFCs make to photochemical ozone production. Photochemical ozone creation potentials (POCPs) have been calculated using a photochemical trajectory model. The POCPs of the HCFCs and HFCs are low, indicating that these compounds do not have a large potential to contribute to ground-level ozone formation. This results from their low reactivity compared to the other, more reactive, organic compounds ...

Photochemical ozone creation potentials for a large number of reactive hydrocarbons under European conditions

A photochemical trajectory model is used to describe the ozone production from the oxidation of methane and 95 other hydrocarbons in the presence of sunlight and NO x in air parcels advected across north west Europe towards the British Isles. By adding a small additional mass emission of each hydrocarbon in turn, additional ozone production was stimulated. A photochemical ozone creation potential (POCP) index was generated from the model results showing the relative importance of each hydrocarbon in ozone formation, on a mass emitted basis. Aromatic and olefinic hydrocarbons showed the highest POCP values with halocarbons the lowest. Using the POCP index, motor vehicle exhaust is seen to exhibit the highest ozone-forming potential of all the hydrocarbon emission source categories evaluated. Toluene, n-butane, ethylene and the xylenes, alone, account for over one third of the ozone forming potential of European emissions. Certain hydrocarbons, including acetone and methyl acetate, show significantly lower POCPs and have considerable potential as candidates for substitution in industrial or chemical processes and as solvents.

Photochemical ozone creation potentials for a large number of reactive hydrocarbons under European conditions

Photochemical ozone creation potentials for a large number of reactive hydrocarbons under European conditions

Hydrocarbon reactivity and ozone formation in Europe

Several studies have shown that in qualitative terms VOCs can be ranked in terms of their importance to ozone formation in Europe, using a so-called photochemical ozone creation potential (POCP). However, all studies showed significant variability in the quantitative POCP values assigned to each VOC species. In this paper, we make use of a complex photochemical oxidant model to quantify how the reaction time-scales of emitted VOC and their reaction products vary with geographical location and time of year. The model is used to evaluate monthly POCP values for 9 hydrocarbon and oxygenated VOC compounds for a cross-section across Europe. Calculations are presented to illustrate the gradients in POCP values of one species,n-butane, across the whole of Europe for April and June 1989. We discuss some of the factors responsible for these variations.

Photochemical Ozone Creation Potentials: A study of Different Concepts

Photochemical ozone creation potentials (POCP) have been calculated for 75 organic compounds and carbon monoxide. The creation potentials are calculated using different concepts; peak ozone concentrations and the average formation of ozone, including the amount deposited, during two or four days. The calculations were made by a single-box trajectory model with meteorological and chemical conditions chosen to correspond to a summer high-pressure situation in southern Sweden. Under these conditions, over a 96-hour average, POCPs show that ethene and acrolein are the most efficient ozone producers, followed by higher alkenes, aromatics, alkanes and ethers which can be considered as mediate ozone producers. Chlorinated species, alcohols and ketones are very weak producers of ozone. The relative POCPs differ depending on the method of calculation and the chemical (NOX) environment.

The magnitude and relative environmental impact of air pollutant emissions from aerosol industry products

Abstract Aerosol industry products have in the past been a major source of CFC emissions. This situation has changed very rapidly and in developed countries CFC use has been eliminated other than in a few essential medical products. Current and likely future air pollutant emissions from aerosol industry products are evaluated in terms of their stratospheric ozone depletion potential, global wanning potential and photochemical ozone creation potential. Environmental impacts of future emissions are likely to be minimal in comparison to those from other air pollution sources.