Peroxyacetyl nitrate

• PAN
• Acetylpernitrat

Gaseous

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Peroxyacetyl nitrate ( PAN) is a trace gas in the atmosphere and at the same time an air pollutant.

Formation

PAN is formed in the atmosphere by photochemical oxidation of hydrocarbons to Peressigsäureradikalen in the presence of nitrogen dioxide ( NO2), so it is - because it is not emitted directly into the atmosphere - a secondary air pollutant. It is adjacent to ozone and hydrogen peroxide ( H2O2) the most important component of photochemical smog, and closely coupled to its concentration in the course of the ozone concentration.

In addition to PAN Peroxypropionyl, butyrylnitrat - and - benzoylnitrat (PPN, PBN, PbZn ) occur ( generally peroxy acyl nitrate). Observed were also chlorinated forms. However, PAN is the most important compound of this group. PAN and its homologues reach in urban areas about 5 to 20 % of the concentration of ozone, typically about 10%. PAN decomposes depends on the temperature back to NO2 and the Peroxyacetylradikal. Due to this stability it can be transported over long distances, and acts as carrier of nitrogen oxides in the clean air area.

The decomposition of PAN in the atmosphere is primarily thermally; thus the long-range transport of PAN is made by cold zones of the atmosphere, while the degradation takes place in warmer layers. Also occurs degradation by UV photolysis. PAN presents as both a source and a drain of ROx and NOx radicals represent, and is therefore also referred to as a reservoir gas.

Synthesis

PAN may be prepared in a lipophilic solvent of peracetic acid. These degassed n- tridecane and peracetic acid are presented in the cooled with an ice bath round bottom flask and carefully mixed with 98 % sulfuric acid. Concentrated nitric acid is then added dropwise. After completion of the reaction is washed four times with ice-water, the aqueous, strongly acidic phase was discarded and the organic phase dried with anhydrous sodium sulfate. With this procedure arises in the n- tridecane dissolved PAN, which can be further used by stripping with an inert gas (such as helium, or nitrogen), and collecting in the cold trap. In this synthesis must proceed with great caution and care, as they may explode.

Alternatively, the PAN can be obtained by synthesis in the gaseous phase. For a gas mixture of acetone and nitrogen dioxide ( NO2) is photolyzed by a mercury vapor lamp. So byproduct methyl nitrate ( CH3ONO2 ).

Readings

The natural concentration of PAN in the atmosphere is below 0.1 ľg/m3. In West German cities measurements showed half-hour values ​​up to about 25 ľg/m3, known peak values ​​( eg measured in Los Angeles in the second half of the 20th century ) are sometimes more than 200 ľg/m3 ( PAN at 1 ppm corresponds to 4370 micrograms / m3). Because of the elaborate measurement methodology to lie PAN usually only point measurements before, so not comparable with ozone measurement series.

Adverse effects

PAN has a higher toxicity than ozone. The eye irritation occur during photochemical smog are less caused by the difficult water-soluble ozone than by PAN and accompanying trace gases. In addition, PAN is discussed as a factor in skin carcinogenesis: in particular chlorinated derivatives, but also PAN itself, are considered mutagenic.

Harmful effects on plants are also occupied by PAN: It damages especially the spongy tissue of sheets, starting from the slit openings. Therefore, symptoms of pure PAN injury are often first on the underside of leaves was observed ( silver to bronze coloration with subsequent necrosis). Certain sensitive plant species can therefore be used for biomonitoring of PAN, such as bush beans or Small Nettle (Urtica urens ).

In the thermal and the photolytic decomposition of peroxyacetyl nitrate nitrogen oxides are formed which promote ozone production in the lower troposphere.

PAN acts as a greenhouse gas in the atmosphere.

Acute and Chronic Toxicity

PAN causes acute eye irritation in humans. These sufficed in a volunteer study in 1961 a concentration of 4.95 mg/m3 for 10 to 15 minutes. A more recent study from 1987 showed the same symptoms even at 0.64 mg/m3 (0.13 ppm). People with COPD reported a gain of disease symptoms when they were exposed to 0.059 mg/m3 PAN. Mice showed an increased susceptibility to infections caused by Streptococcus pyogenes causing death after they were exposed for three hours a dose from 14.8 to 28.4 mg/m3 PAN. In long-term experiments with rats over 4 weeks to 6 months amounts yielded from 11.8 ppm (4 weeks) and 74 mg/m3 (6 months) increased mortality and a variety of symptoms such as increased platelet number, enlargement of the lungs, abnormal behavior, halt of growth, and severe inflammation to metaplasia and hyperplasia of the respiratory tract. In bacteria (Salmonella typhimurium) and lymphocytes from mice seemed PAN genotoxic and cytotoxic at higher concentrations