{{chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 411625303 | ImageFile = Peroxyacetyl nitrate Structural formula V1.svg | ImageFile1 = Peroxyacetyl-nitrate-3D-balls.png | PIN = Acetic nitric peroxyanhydride | OtherNames = {{ubl| |PAN |peroxyacetyl nitrate |α-oxoethylperoxylnitrate }} |Section1={{Chembox Identifiers | Abbreviations = PAN | CASNo_Ref = {{cascite|correct|CAS}} | CASNo = 2278-22-0 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = SQ8V0P4N89 | EINECS = 218-905-6 | PubChem = 16782 | ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}} | ChemSpiderID = 15907 | StdInChI_Ref = {{stdinchicite|changed|chemspider}} | StdInChI = 1S/C2H3NO5/c1-2(4)7-8-3(5)6/h1H3 | StdInChIKey_Ref = {{stdinchicite|changed|chemspider}} | StdInChIKey = VGQXTTSVLMQFHM-UHFFFAOYSA-N | SMILES = CC(OO[N+]([O-])=O)=O | RTECS = | MeSHName = | ChEBI_Ref = {{ebicite|correct|EBI}} | ChEBI = | KEGG_Ref = {{keggcite|correct|kegg}} | KEGG = }} |Section2={{Chembox Properties | Properties_ref = {{cn|date=January 2026}} | Formula = {{chem2|C2H3NO5}} | C=2 |H=3 |N=1 |O=5 | Appearance = | Density = | MeltingPt = | MeltingPt_notes = | BoilingPt = | BoilingPt_notes = | Solubility = {{val|146|u=g/L}} | SolubleOther = | Solvent = | LogP = {{val|-0.19}} | VaporPressure = {{cvt|29.2|mmHg}} | HenryConstant = {{val|2.78|e=-4|u=m3·atm|up=mol|fmt=none}} | AtmosphericOHRateConstant = {{val|e=-13|u=cm3|up=(mol·s)}} | pKa = | pKb = }} |Section3={{Chembox Structure | CrystalStruct = | Coordination = | MolShape = }} |Section4={{Chembox Thermochemistry | DeltaHf = | DeltaHc = | Entropy = | HeatCapacity = }} |Section5={{Chembox Pharmacology | AdminRoutes = | Bioavail = | Metabolism = | HalfLife = | ProteinBound = | Excretion = | Legal_status = | Legal_US = | Legal_UK = | Legal_AU = | Legal_CA = | Pregnancy_category = | Pregnancy_AU = | Pregnancy_US = }} |Section6={{Chembox Explosive | ShockSens = | FrictionSens = | DetonationV = | REFactor = }} |Section7={{Chembox Hazards | MainHazards = | NFPA-H = | NFPA-F = | NFPA-R = | NFPA-S = | HPhrases = | PPhrases = | GHS_ref = | FlashPt = | AutoignitionPt = | ExploLimits = | PEL = }} |Section8={{Chembox Related | OtherAnions = | OtherCations = | OtherFunction = | OtherFunction_label = | OtherCompounds = }} }}
'''Peroxyacetyl nitrate''' is a peroxyacyl nitrate. It is a secondary pollutant present in photochemical smog and PAN concentrations can be sensitive to precursor emissions.<ref name=":0">{{Cite journal |last=E V |first=Fischer |date=March 14, 2014 |title=Atmospheric Peroxyacetyl Nitrate (PAN): a global budget and source attribution |journal= Atmospheric Chemistry and Physics|volume=14 |issue=5 |pages=2679–2698 |doi=10.5194/acp-14-2679-2014 |doi-access=free |pmid=33758588 |pmc=7983850 |bibcode=2014ACP....14.2679F }}</ref><ref name=":2">{{Cite journal |last=Shogrin |first=Madison J. |date=February 27, 2024 |title=Changes to Peroxyacyl Nitrates (PANs) Over Megacities in Response to COVID-19 Tropospheric NO2 Reductions Observed by the Cross-Track Infrared Sounder (CrIS) |journal=Geophysical Research Letters|volume=51 |issue=6 |article-number=e2023GL104854 |doi=10.1029/2023GL104854 |doi-access=free |via=Wiley & Sons}}</ref> It is thermally unstable and decomposes into peroxyethanoyl radicals and nitrogen dioxide gas. It is a lachrymatory substance, meaning that it irritates the lungs and eyes.<ref name=":1">{{Cite journal |last=Vyskocil |first=Adolf |date=April 17, 1998 |title=Peroxyacetyl nitrate: review of toxicity |journal=Human & Experimental Toxicology|volume=17 |issue=4 |pages=212–220 |doi=10.1177/096032719801700403 |pmid=9617633 |bibcode=1998HETox..17..212V }}</ref>
Peroxyacetyl nitrate, or PAN, is an oxidant that is more stable than ozone. Hence, it is more capable of long-range transport than ozone. It serves as a carrier for oxides of nitrogen (NOx) into rural regions and causes ozone formation in the global troposphere.<ref name=":0" />
== Atmospheric chemistry == PAN is produced in the atmosphere via photochemical oxidation of hydrocarbons (e.g. Alkenes, Aromatics, and isoprenes).<ref name=":3">{{Cite journal |last=Xueqi |first=Qiao |date=June 1, 2023 |title=Strong relations of peroxyacetyl nitrate (PAN) formation to alkene and nitrous acid during various episodes |journal=Environmental Pollution|volume=326 |article-number=121465 |doi=10.1016/j.envpol.2023.121465 |pmid=36958651 |bibcode=2023EPoll.32621465Q }}</ref><ref name=":1" /> Carbonyls (oxidized VOCs) create acyl radicals which then become peroxyacetic acid (PA) radicals. Acetaldehyde is the dominant carbonyl species to produce PA radicals followed by Methylglyoxal, combined they can account for up to 80% of PA radical formation.<ref name=":0" /><ref name=":3" /> The PA radicals can reversibly react with nitrogen dioxide ({{chem2|NO2}}) to form PAN.<ref name=":0" /> Night-time reaction of acetaldehyde with nitrogen trioxide is another possible source.<ref name=":3" /> Since there are no direct PAN emissions, it is a secondary pollutant. Next to ozone and hydrogen peroxide ({{chem2|H2O2}}), it is one of the most important components of photochemical smog.{{cn|reason=The given ref doesn't even contain the word smog once or mention hydrogen peroxide...|date=January 2026}}
:R{{sub|1}} : {{chem2|CH3C(O)OO + NO2 + M <-> PAN + M }}
:R{{sub|2}} : {{chem2|CH3CHO + OH}} {{overset|{{chem2|O2}}|{{arrow}}}} {{chem2|CH3C(O)OO + H2O}}
:R{{sub|2}} : {{chem2|CH3COCHO + ''hv''}} {{overset|{{chem2|O2}}|{{arrow}}}} {{chem2|CH3C(O)OO + HCO}}
Other peroxyacyl nitrates 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, these peroxy-nitrates are stable and can be transported over long distances, providing nitrogen oxides to otherwise unpolluted areas. At higher temperatures, they decompose into {{chem2|NO2}} and the peroxyacyl radical.<ref name=":0" />
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 photolyzed by UV radiation. It is a reservoir gas that serves both as a source and a sink of {{chem2|RO_{x}-}} and {{chem2|NO_{x} }} radicals. Nitrogen oxides from PAN decomposition enhance ozone production in the lower troposphere.<ref name=":0" />
The natural concentration of PAN in the atmosphere is below {{val|0.1|u=μg/m3}}. Measurements in German cities showed values up to {{val|25|u=μg/m3}}. Peak values above {{val|200|u=μg/m3}} have been measured in Los Angeles in the second half of the 20th century ({{val|4.37|u=μg/m3}} of PAN corresponds to one part per billion (ppb)).<ref name=":0" /> Due to the complexity of the measurement setup, only sporadic measurements are available. The satellite based Cross-Track Infrared sounder (CrIS) instrument is able to provide mid-tropospheric PAN measurements on a global scale.<ref name=":2" /><ref name=":4">{{Cite journal |last=Vivienne H. |first=Payne |date=June 10, 2022 |title=Satellite measurements of peroxyacetyl nitrate from the Cross-Track Infrared Sounder: comparison with ATom aircraft measurements |journal= Atmospheric Measurement Techniques|volume=15 |issue=11 |pages=3497–3511 |doi=10.5194/amt-15-3497-2022 |doi-access=free |bibcode=2022AMT....15.3497P }}</ref>
PAN is a greenhouse gas.
== Sensitivity == PAN has a sensitivity to precursor emissions, mainly from VOCs and {{chem2|NO_{x} }}.<ref name=":0" /><ref name=":2" /> PANs sensitivity towards VOCs is greater than that of {{chem2|NO_{x} }}. VOC reductions have more of an effect on PA radicals than on {{chem2|NO_{x} }}.<ref name=":3" /> Notably, global emissions of precursor during Covid-19 demonstrated that PAN concentrations do not always decrease with a decrease in {{chem2|NO_{x} }} concentrations.<ref name=":2" /><ref name=":5">{{Cite journal |last=Yulu |first=Qiu |date=September 16, 2020 |title=Markedly Enhanced Levels of Peroxyacetyl Nitrate (PAN) During COVID-19 in Beijing |journal=Geophysical Research Letters|volume=47 |issue=19 |article-number=e2020GL089623 |doi=10.1029/2020GL089623 |doi-access=free |bibcode=2020GeoRL..4789623Q }}</ref> Similarly, PAN responds non-linearly to precursor changes.<ref name=":0" /><ref name=":2" /> Alkenes and oxidized VOCs strongly influence the formation of PA radicals.<ref name=":3" /> Meteorological effects also influence the availability of these radicals and hence PAN formation.<ref name=":5" />
== Synthesis == PAN can be produced in a lipophilic solvent from peroxyacetic acid.<ref>{{Cite journal |last1=Gaffney |first1=J.S. |last2=Fajer |first2=R. |last3=Senum |first3=G.I. |date=January 1984 |title=An improved procedure for high purity gaseous peroxyacyl nitrate production: Use of heavy lipid solvents |journal=Atmospheric Environment |language=en |volume=18 |issue=1 |pages=215–218 |doi=10.1016/0004-6981(84)90245-2|bibcode=1984AtmEn..18..215G }}</ref> For the synthesis, concentrated sulfuric acid is added to degassed ''n''-tridecane and peroxyacetic acid in an ice bath. Next, concentrated nitric acid is added.<ref name=":6">{{Cite journal |last1=Talukdar |first1=Ranajit K. |last2=Burkholder |first2=James B. |last3=Schmoltner |first3=Anne-Marie |last4=Roberts |first4=James M. |last5=Wilson |first5=Robert R. |last6=Ravishankara |first6=A. R. |date=1995-07-20 |title=Investigation of the loss processes for peroxyacetyl nitrate in the atmosphere: UV photolysis and reaction with OH |journal=Journal of Geophysical Research: Atmospheres |language=en |volume=100 |issue=D7 |pages=14163–14173 |doi=10.1029/95JD00545 |bibcode=1995JGR...10014163T |issn=0148-0227}}</ref><ref name=":7" />
As an alternative, PAN can also be synthesized in the gas phase via photolysis of acetone and {{chem2|NO2}} with a mercury lamp. Methyl nitrate ({{chem2|CH3ONO2}}) is created as a by-product.<ref name=":7">{{Cite journal |last1=Nielsen |first1=Torben |last2=Hansen |first2=Anne Maria |last3=Thomsen |first3=Erling Lund |date=January 1982 |title=A convenient method for preparation of pure standards of peroxyacetyl nitrate for atmospheric analyses |journal=Atmospheric Environment |language=en |volume=16 |issue=10 |pages=2447–2450 |doi=10.1016/0004-6981(82)90134-2|bibcode=1982AtmEn..16.2447N }}</ref>
== Atmospheric effects == Seasonal cycles of PAN have been observed. Meteorological effects such as temperatures, wind patterns, and the availability of radicals influence PANs stability as well as transportation in the atmosphere.<ref name=":0" /><ref name=":5" /> During the springtime in the northern hemisphere, high concentrations are attributed to an increase in photochemical activity.<ref name=":5" /> In addition, concentrations of PAN increase due to it having a relatively large lifetime against thermal decomposition.<ref name=":0" /> Transportation of PAN can also occur by wildfire smoke moving it into an otherwise unpolluted region.<ref name=":2" /> In the northern hemisphere winter however, PAN levels become limited when there are reduced hydrocarbons, {{chem2|NO2}}, and low solar radiation.<ref name=":0" />
== Toxicity == The toxicity of PAN is similar to that of {{chem2|NO2}} but higher than sulfur dioxide ({{chem2|SO2}}). Populations with pulmonary disease tend to be more sensitive to the toxic effects of PAN. Eye irritation from photochemical smog can be caused by an increase in PAN levels. Concentrations at or above {{val|0.64|u=mg/m3}} increase the likelihood of eye irritation. PAN is a very weak mutagen.<ref name=":1" />
==References== {{reflist}}
Category:Organic peroxides Category:Nitrate esters Category:Organic peroxide explosives Category:Explosive chemicals Category:Acetyl compounds Category:Pollutants Category:Smog