Peroxyacylnitrates

Photochemical oxidants are atmospheric pollutants produced by a series of reactions between hydrocarbons and oxides of nitrogen in the presence of sunlight. The recognized photochemical oxidants that have been measured in ambient air are ozone, the peroxyacylnitrates (mostly as PAN), and hydrogen peroxide. ... 

Chemical radicals—such as hydroxyl, peroxyhydroxyl, and various alkyl and aryl species—have either been observed in laboratory studies or have been postulated as photochemical reaction intermediates. Atmospheric photochemical reactions also result in the formation of finely divided suspended particles (secondary aerosols), which create atmospheric haze. Their chemical content is enriched with sulfates (from sulfur dioxide), nitrates (from nitrogen dioxide, nitric oxide, and peroxyacylnitrates), ammonium (from ammonia), chloride (from sea salt), water, and oxygenated, sulfiirated, and nitrated organic compounds (from chemical combination of ozone and oxygen with hydrocarbon, sulfur oxide, and nitrogen oxide fragments). ... 

The peroxyacylnitrates were first identified in % as the primary cause of the undersurface glazing and bronzing on some broadleaved plants. PAN has since been implicated in numerous pollution episodes in southern California. Its importance in other metropolitan and rural areas in the United States and throughout the world is uncertain, although symptoms have been reported elsewhere. The reason is that oxidant concentrations in other parts of the world are much lower than those reported in California, and monitoring networks have not looked for PAN or its homologues. The report by Penkett et al. was the first to come from Europe. 

The peroxyacylnitrates are the most phytotoxic of the known photochemical oxidants. The toxicity of the known homologues is inversely correlated with molecular weight. PAN is the best known and has been studied most, because of its usual presence in photochemical atmospheres. 

Chemical Basis of Toxicity The toxicity of the peroxyacylnitrates to plants can be the result of several different processes. Any chemical explanation of the toxicity will have to explain the increasing toxicity of the series PAN, PPN, PBN, and PBzN. Three hypotheses have been tested the more toxic homologues are more readily taken up by the... 

Phlogiston a material once thought to be an element responsible for combustion Phospholipid lipid containing phosphorus derived from phosphoric acid Photochemical Oxidants air pollutants produced when hydrocarbons, nitrogen oxides, and other chemicals react under the influence of sunlight, for example, ozone, peroxyacylnitrates (PAN)... 

Carbon monoxide is oxidized in the troposphere ((133) and (134)). With a high concentration of nitric oxide in the troposphere, reactions (135) and (136) take place. This sequence is a formation of ozone catalyzed by nitric oxide. If the nitric oxide concentration is too low, the perhydryl radicals decompose ozone to form hydroxyl radicals (136). Ozone and peroxyacylnitrates PAN are the major toxins of smog. Peroxyacylnitrates are formed from aldehydes in a reaction catalyzed by nitric oxide. 

Oxidants formed in the atmosphere mainly by photochemical activity are O3, NO2 and peroxyacylnitrates. 

These properties may account for their biological behaviour. Peroxyacylnitrates — mainly represented by peroxyacetylnitrate, indicated as PAN — originate in the atmosphere over towns and industrial areas, through a mechanism not fully clarified, from olefins, and other hydrocarbons (car exhausts, fuel from car tank evaporation, gas formed in the refineries of crude oil) under photochemical conditions by NOx in the presence of O2 (Stephen, 1969). 

Peroxyacylnitrates constitute a part (about 10%) of the total oxidants and are formed in the city atmosphere in conditions of bright light. 

The intermediates formed in AOPs sometimes are more toxic than the parent compounds and are required to be decomposed completely using either combination of AOPs or combination of AOP and some other treatment methods such as adsorption and biodegradation. Carbonyl compounds, particularly aldehydes, are quite toxic, and some of the secondary compounds formed from aldehydes, especially peroxyacylnitrates are more dangerous than the parent compounds. Organic peroxy radical (ROj) reactions are of significance because they represent an important class of intermediates formed in the oxidation process of hydrocarbons (15). Intermediates such as ethers and alcohols have enhanced reactivity toward hydroxyl radical. The rate constant of oxidation of these compounds is of similar order of magnitude as of the alkanes. 

Nitrogen and simultaneously formed non-organic (H2O2) and organic (ROOH) peroxides and peroxyacylnitrates are the strongest photo- and phyto oxidants. The increase of the concentration of these secondary pollutants in the atmosphere causes a decrease in bio-... 

Figure 4 ranks eye-response as the arithmetic mean response time. Styrene and a-methylstyrene are the most reactive species partly because of their benzyl groups. Heuss and Glasson (15) showed that peroxy-benzoylnitrate (PBzN), a specific lachrymator produced in these systems, is 200 times more reactive than peroxyacylnitrate, which itself is a fairly potent lachrymator. Tetrahydrofuran, mesityl oxide, and trans-2-butene are high in eye irritation (Figure 4). 

Peroxyacylnitrate (PAN) is one of the components of smog. It is a compound of C, H, N, and O. Determine the percent composition of oxygen and the empirical formula from the following percent composition by mass 19.8 percent C, 2.50 percent H, 11.6 percent... 

Table 10 gives an example of the composition of photochemical smog. Smog causes respiratory problems (which can be extremely serious), irritates the eyes, reduces the visibility and causes damage to the vegetation. Peroxyacylnitrates and ozone are amongst the most dangerous compounds. 

Data have also been obtained for various other peroxyacylnitrate species formed from a number of different VOCs. Structure-reactivity relationships for the thermal stability of PAN type species have been established which provide the needed information for assessing the transport of NOy in this form, and also the relationships required in order to estimate the relative rates of the reactions of RO2 with NO (leading to ozone production) and NO2 (leading to the PAN reservoirs) have been established. Although the peroxyacylnitrates are the most stable, other peroxynitrates could also be significant reservoirs for NOx in the coldest regions of the troposphere. 

Yes, it is very bad for the respiratory system. It is generated on hot sunny summer days when the sunlight acts on mixtures of hydrocarbons and nitrogen oxides emitted from car exhausts to form peroxyacylnitrates (or PANs, with general formula RCOOONO2 with R = alkyl). These are the compounds which typically make your eyes water on a hot summer s day in city streets. Ozone is formed from them when they decompose. 

Whitehouse et al. (2004a,b) applied these methods to MCM v2. They reduced the number of species in the mechanism by approximately 50%. They extended the process by lumping species, such as peroxyacylnitrates, with similar lifetimes and reaction patterns. This procedure allowed reduction of the number of species to 35% of the original number in MCM v2. 

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