Peroxyacetyl nitrate is a peroxyacyl nitrate. It is a secondary

pollutant A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like o ...

present in

photochemical smog Smog, or smoke fog, is a type of intense air pollution. The word "smog" was coined in the early 20th century, and is a portmanteau of the words ''smoke'' and ''fog'' to refer to smoky fog due to its opacity, and odor. The word was then inten ...

. It is thermally unstable and decomposes into peroxyethanoyl radicals and

nitrogen dioxide Nitrogen dioxide is a chemical compound with the formula . It is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year for use primarily in the productio ...

gas. It is a

lachrymatory Lachrymatory or lacrymatory may refer to: * Something that has the effect of ''lachrymation'', causing the secretion of tears * Tear gas, known formally as a ''lachrymatory agent'' or ''lachrymator'' * A lacrymatory, a small vessel of terra ...

substance, meaning that it irritates the lungs and eyes. Peroxyacetyl nitrate, or PAN, is an oxidant that is more stable than

ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lowe ...

. Hence, it is more capable of long-range transport than ozone. It serves as a carrier for

oxides of nitrogen Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds: Charge-neutral *Nitric oxide (NO), nitrogen(II) oxide, or nitrogen monoxide *Nitrogen dioxide (), nitrogen(IV) oxide *Nitrogen trioxide (), or ...

(NOx) into rural regions and causes ozone formation in the global

troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From t ...

Atmospheric chemistry

PAN is produced in the atmosphere via photochemical oxidation of

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...

s to

peroxyacetic acid Peracetic acid (also known as peroxyacetic acid, or PAA) is an organic compound with the formula CH3CO3H. This peroxy acid is a colorless liquid with a characteristic acrid odor reminiscent of acetic acid. It can be highly corrosive. Peracetic ac ...

radicals in the presense of

(NO₂). Since there are no direct emissions, it is a secondary pollutant. Next to

and

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%–6 ...

(H₂O₂), it is an important component of

. Further

peroxyacyl nitrates In organic chemistry, peroxyacyl nitrates (also known as Acyl peroxy nitrates, APN or PANs) are powerful respiratory and eye irritants present in photochemical smog. They are nitrates produced in the thermal equilibrium between organic peroxy r ...

in the atmosphere are peroxypropionyl nitrate (PPN), peroxybutyryl nitrate (PBN), and peroxybenzoyl nitrate (PBzN). Chlorinated forms have also been observed. PAN is the most important peroxyacyl nitrate. PAN and its homologues reach about 5 to 20 percent of the concentration of ozone in urban areas. At lower temperatures, it is stable and can be transported over long distances, providing nitrogen oxides to otherwise unpolluted areas. At higher temperatures, it decomposes into NO₂ and the peroxyacetyl radical. The decay of PAN in the atmosphere is mainly thermal. Thus, the long-range transport occurs through cold regions of the atmosphere, whereas the decomposition takes place at warmer levels. PAN can also be photolysed by UV radiation. It is a reservoir gas that serves both as a source and a sink of RO_x- and NO_x radicals.J. S. Gaffney et al.: ''Peroxyacyl Nitrates''. In: ''The Handbook of Environmental Chemistry.'' Vol. 4, Part B, S. 1–38; Hrsg.: Hutzinger, O., Springer, 1989. Nitrogen oxides from PAN decomposition enhance ozone production in the lower

. The natural concentration of PAN in the atmosphere is below 0,1 µg/m³. Measurements in German cities showed values up to 25 µg/m³. Peak values above 200 µg/m³ have been measured in

Los Angeles Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the world' ...

in the second half of the 20th century (1 ppm of PAN corresponds to 4370 µg/m³). Due to the complexity of the measurement setup, only sporadic measurements are available. PAN is a

greenhouse gas A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxide (), methane ...

Synthesis

PAN can be produced in a lipophilic solvent from

.R. K. Talukdar, J. B. Burkholder, A.-M. Schmoltner, J. M. Roberts, R. R. Wilson, A. R. Ravishankara: ''Investigation of the loss processes for peroxyacetyl nitrate in the atmosphere: UV photolysis and reaction with OH''. In: ''

Journal of Geophysical Research The ''Journal of Geophysical Research'' is a peer-reviewed scientific journal. It is the flagship journal of the American Geophysical Union. It contains original research on the physical, chemical, and biological processes that contribute to the u ...

.'' Band 100, Nr. D7, 1995, S. 14163–14173, doi:10.1029/95JD00545.T. Nielsen, A.M. Hansen, E. L. Thomsen: ''A convenient method for preparation of pure standards of peroxyacetyl nitrate for atmospheric analyses.'' In: ''

Atmospheric Environment An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

.'' Band 16, Nr. 10, 1982, S. 2447–2450, doi:10.1016/0004-6981(82)90134-2.J. S. Gaffney, R. Fajer, G. I. Senum: ''An improved procedure for high purity gaseous peroxyacyl nitrate production: Use of heavy lipid solvents.'' In: ''Atmospheric Environment.'' Band 18, Nr. 1, 1984, S. 215–218, doi:10.1016/0004-6981(84)90245-2.J. L. Fry ''Spectroscopy and kinetics of atmospheric reservoir species: HOONO, CH₃C(O)OONO₂, CH₃OOH and HOCH₂OOH''. ''Ph.D. Thesis'', 2006. For the synthesis, concentrated sulfuric acid is added to degassed ''n''-

tridecane Tridecane or ''n''-tridecane is an alkane with the chemical formula CH3(CH2)11CH3. Tridecane is a combustible colourless liquid. In industry, they have no specific value aside from being components of various fuels and solvents. In the research ...

and peroxyacetic acid in an ice bath. Next, concentrated nitric acid is added. As an alternative, PAN can also be synthesized in the gas phase via photolysis of

acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscible wi ...

and NO₂ with a mercury lamp.P. Warneck, T. Zerbach: ''Synthesis of Peroxyacetyl Nitrate in Air by Acetone Photolysis''. In: ''

Environmental Science & Technology ''Environmental Science & Technology'' is a biweekly peer-reviewed scientific journal published since 1967 by the American Chemical Society. It covers research in environmental science and environmental technology, including environmental policy. ...

'', 1992, 26, S. 74, doi:10.1021/es00025a005.

Methyl nitrate Methyl nitrate is the methyl ester of nitric acid and has the chemical formula CH3NO3. It is a colourless explosive volatile liquid. Synthesis It can be produced by the condensation of nitric acid and methanol: :CH3OH + HNO3 → CH3NO3 + H2O A ...

(CH₃ONO₂) is created as a by-product.

Toxicity

The toxicity of PAN is higher than that of ozone. Eye irritations from photochemical smog are caused more by PAN and other trace gases than by ozone, which is only sparingly soluble. PAN is potentially involved in the creation of skin cancer. Especially chlorine-containing derivatives are considered

mutagen In genetics, a mutagen is a physical or chemical agent that permanently changes genetic material, usually DNA, in an organism and thus increases the frequency of mutations above the natural background level. As many mutations can cause cancer i ...

References

Organic peroxides Nitrate esters Organic peroxide explosives Explosive chemicals {{ester-stub