Peroxyacetyl nitrate

Peroxyacetyl nitrate
Names
Preferred IUPAC name
Acetic nitric peroxyanhydride
Other names
PAN
peroxyacetyl nitrate
α-oxoethylperoxylnitrate
Identifiers
3D model (JSmol)
Abbreviations PAN
ChemSpider
ECHA InfoCard 100.017.187 Edit this at Wikidata
EC Number
  • 218-905-6
UNII
  • InChI=1S/C2H3NO5/c1-2(4)7-8-3(5)6/h1H3 ☒N
    Key: VGQXTTSVLMQFHM-UHFFFAOYSA-N ☒N
  • CC(OO[N+]([O-])=O)=O
Properties
C2H3NO5
Molar mass 121.05 g mol−1
1.46 × 10 5 mg l−1 at 298 K
log P −0.19
Vapor pressure 29.2 mmHg at 298 K
0.000278 m3 atm mol−1 at 298 K
Atmospheric OH rate constant
 10−13 cm3 molecule−1 s−1 at 298 K
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Peroxyacetyl nitrate is a peroxyacyl nitrate.[1] It is a secondary pollutant present in photochemical smog and PAN concentrations can be sensitive to precursor emissions.[2][1] 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.[3]

Peroxyacetyl nitrate, or PAN, is an oxidant that is more stable than ozone.[1] Hence, it is more capable of long-range transport than ozone.[1] It serves as a carrier for oxides of nitrogen (NOx) into rural regions and causes ozone formation in the global troposphere.[1]

Atmospheric chemistry

PAN is produced in the atmosphere via photochemical oxidation of hydrocarbons (e.g. Alkenes, Aromatics, and isoprenes).[4][3] Carbonyls (oxidized VOCs) create acyl radicals which then become peroxyacetic acid (PA) radicals.[4] 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.[1][4] The PA radicals can reversibly react with nitrogen dioxide (NO2) to form PAN.[1] Night-time reaction of acetaldehyde with nitrogen trioxide is another possible source.[4] Since there are no direct PAN emissions, it is a secondary pollutant.[1] Next to ozone and hydrogen peroxide (H2O2), it is an important component of photochemical smog.[1]

[1]

Other peroxyacyl nitrates in the atmosphere are peroxypropionyl nitrate (PPN), peroxybutyryl nitrate (PBN), and peroxybenzoyl nitrate (PBzN). Chlorinated forms have also been observed.[1] 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.[1] At lower temperatures, these peroxy-nitrates are stable and can be transported over long distances,[1] providing nitrogen oxides to otherwise unpolluted areas. At higher temperatures, they decompose into NO2 and the peroxyacyl radical.[1]

The decay of PAN in the atmosphere is mainly thermal.[1] Thus, the long-range transport occurs through cold regions of the atmosphere, whereas the decomposition takes place at warmer levels.[1] PAN can also be photolyzed by UV radiation.[1] It is a reservoir gas that serves both as a source and a sink of ROx- and NOx radicals.[1] Nitrogen oxides from PAN decomposition enhance ozone production in the lower troposphere.[1]

The natural concentration of PAN in the atmosphere is below 0.1 μg/m3.[1] Measurements in German cities showed values up to 25 μg/m3.[1] Peak values above 200 μg/m3 have been measured in Los Angeles in the second half of the 20th century (1 ppb of PAN corresponds to 4.37 μg/m3).[1] Due to the complexity of the measurement setup, only sporadic measurements are available.[2][5] The satellite based Cross-Track Infrared sounder (CrIS) instrument is able to provide mid-tropospheric PAN measurements on a global scale.[5][2]

PAN is a greenhouse gas.

Sensitivity

PAN has a sensitivity to precursor emissions, mainly from VOCs and NOx.[1][2][4] PANs sensitivity towards VOCs is greater than that of NOx.[4] VOC reductions have more of an effect on PA radicals than on NOx.[4] Notably, global emissions of precursor during Covid-19 demonstrated that PAN concentrations do not always decrease with a decrease in NOx concentrations.[2][6] Similarly, PAN responds non-linearly to precursor changes.[1][2] Alkenes and oxidized VOCs strongly influence the formation of PA radicals.[4] Meteorological effects also influence the availability of these radicals and hence PAN formation.[6]

Synthesis

PAN can be produced in a lipophilic solvent from peroxyacetic acid.[7][8] 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.[8][9]

As an alternative, PAN can also be synthesized in the gas phase via photolysis of acetone and NO2 with a mercury lamp. Methyl nitrate (CH3ONO2) is created as a by-product.[9]

Atmospheric effects

Seasonal cycles of PAN have been observed.[1] Meteorological effects such as temperatures, wind patterns, and the availability of radicals influence PANs stability as well as transportation in the atmosphere.[1][6] During the springtime in the northern hemisphere, high concentrations are attributed to an increase in photochemical activity.[6] In addition, concentrations of PAN increase due to it having a relatively large lifetime against thermal decomposition.[1] Transportation of PAN can also occur by wildfire smoke moving it into an otherwise unpolluted region.[2] In the northern hemisphere winter however, PAN levels become limited when there is reduced hydrocarbons, NO2, and low solar radiation.[1]

Toxicity

The toxicity of PAN is similar to that of NO2 but higher than sulfur dioxide (SO2).[3] Populations with pulmonary disease tend to be more sensitive to the toxic effects of PAN.[3] Eye irritation from photochemical smog can be caused by an increase in PAN levels.[3] Concentrations at or above 0.64 mg/m3 increase the likelihood of eye irritation.[3] PAN is a very weak mutagen.[3]

References

  1. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab E V, Fischer (March 14, 2014). "Atmospheric Peroxyacetyl Nitrate (PAN): a global budget and source attribution". National Library of Medicine – via NCBI Literature Resources.
  2. ^ a b c d e f g Shogrin, Madison J. (February 27, 2024). "Changes to Peroxyacyl Nitrates (PANs) Over Megacities in Response to COVID-19 Tropospheric NO2 Reductions Observed by the Cross-Track Infrared Sounder (CrIS)". AGU publications – via Wiley & Sons.
  3. ^ a b c d e f g Vyskocil, Adolf (April 17, 1998). "Peroxyacetyl nitrate: review of toxicity". Sage Journal – via National Library of Medicine.
  4. ^ a b c d e f g h Xueqi, Qiao (June 1, 2023). "Strong relations of peroxyacetyl nitrate (PAN) formation to alkene and nitrous acid during various episodes". Science Direct – via Elsevier B.V., its licensors, and contributors.
  5. ^ a b Vivienne H., Payne (June 10, 2022). "Satellite measurements of peroxyacetyl nitrate from the Cross-Track Infrared Sounder: comparison with ATom aircraft measurements". European Geosciences Union – via Creative Commons Attribution.
  6. ^ a b c d Yulu, Qiu (September 16, 2020). "Markedly Enhanced Levels of Peroxyacetyl Nitrate (PAN) During COVID‐19 in Beijing". AGU Publications – via Wiley & Sons.
  7. ^ Gaffney, J.S.; Fajer, R.; Senum, G.I. (January 1984). "An improved procedure for high purity gaseous peroxyacyl nitrate production: Use of heavy lipid solvents". Atmospheric Environment. 18 (1): 215–218. doi:10.1016/0004-6981(84)90245-2.
  8. ^ a b Talukdar, Ranajit K.; Burkholder, James B.; Schmoltner, Anne‐Marie; Roberts, James M.; Wilson, Robert R.; Ravishankara, A. R. (1995-07-20). "Investigation of the loss processes for peroxyacetyl nitrate in the atmosphere: UV photolysis and reaction with OH". Journal of Geophysical Research: Atmospheres. 100 (D7): 14163–14173. doi:10.1029/95JD00545. ISSN 0148-0227.
  9. ^ a b Nielsen, Torben; Hansen, Anne Maria; Thomsen, Erling Lund (January 1982). "A convenient method for preparation of pure standards of peroxyacetyl nitrate for atmospheric analyses". Atmospheric Environment. 16 (10): 2447–2450. doi:10.1016/0004-6981(82)90134-2.
allikas: https://en.wikipedia.org/wiki/Peroxyacetyl_nitrate