Peroxyacetic Nitric Anhydride Research Articles

Comment on “Transport of substantial stratospheric ozone to the surface by a dying typhoon and shallow convection” by Chen et al. (2022)

Abstract. Chen et al. (2022) analyzed the event of rapid nocturnal O3 enhancement (NOE) observed on 31 July 2021 at the surface level in the North China Plain and proposed transport of substantial stratosphere ozone to the surface by Typhoon In-fa followed by downdraft of shallow convection as the mechanism of the NOE event. The analysis seems to be valid from the viewpoint of atmospheric physics. This comment revisits the NOE phenomenon on the basis of the China National Environmental Monitoring Center (CNEMC) network data used in Chen et al. (2022), together with the CNEMC data from Zibo (ZB) and O3, NOx, PAN (peroxyacetic nitric anhydride), and VOC (volatile organic compound) data from the Zibo supersite operated by the China Research Academy of Environmental Sciences (CRAES). We found (a) Ox (O3 + NO2) levels during the NOE period approaching those of O3 during 14:00–17:00 LT, (b) levels of PAN and the relationship between O3 and PAN consistent with dominance of chemical and physical processes within the boundary layer, and (c) estimated photochemical ages of air mass shorter than 1 d and showing no drastic increases during the NOE. We argue that the NOE was not caused by typhoon-induced stratospheric intrusion but originated from fresh photochemical production in the lower troposphere. Our argument is well supported by the analysis of atmospheric transport as well as ground-based remote sensing data.

On quantitative measurements of peroxycarboxylic nitric anhydride mixing ratios by thermal dissociation chemical ionization mass spectrometry

Thermal dissociation chemical ionization mass spectrometry (TD-CIMS) has become an increasingly popular tool for rapid and sensitive quantification of peroxycarboxylic nitric anhydrides (PANs), which are important trace gas constituents of the troposphere. In TD-CIMS, the PANs are thermally dissociated in a heated inlet to NO 2 and peroxyacyl radicals, which are converted in electron transfer reactions with iodide reagent ions to the corresponding carboxylate anions. Here, we evaluate the performance of the TD-CIMS method in the presence of interferences that occur in polluted air masses. Response factors of the TD-CIMS were determined using laboratory-generated air samples and parallel measurements of NO 2 and ΣPAN by blue diode laser thermal dissociation cavity ring-down spectroscopy (TD-CRDS) and of NO y by NO-O 3 chemiluminescence (CL). The TD-CIMS was less sensitive to peroxymethacryloyl nitric anhydride (MPAN) than to other PANs tested, which was rationalized by differences in the temperature dependent loss rates of the peroxyacyl radicals in the heated inlet. To track matrix effects, photochemically generated 13C-labeled PAN was continuously added as an internal standard. The presence of NO or NO 2 in the sample gas mixture resulted in signal suppression, which could be corrected using the internal standard. The presence of organic acids resulted in a redistribution of count intensity between carboxylate anions, impacting the instrument's ability to accurately quantify PANs other than peroxyacetic nitric anhydride under moderately polluted conditions.

Formaldehyde and its relation to CO, PAN, and SO<sub>2</sub> in the Houston-Galveston airshed

Abstract. The Houston-Galveston Airshed (HGA) is one of the major metropolitan areas in the US that is classified as a nonattainment area of federal ozone standards. Formaldehyde (HCHO) is a key species in understanding ozone related air pollution; some of the highest HCHO concentrations in North America have been reported for the HGA. We report on HCHO measurements in the HGA from summer 2006. Among several sites, maximum HCHO mixing ratios were observed in the Houston Ship Channel (HSC), a region with a very high density of industrial/petrochemical operations. HCHO levels at the Moody Tower (MT) site close to downtown were dependent on the wind direction: southerly maritime winds brought in background levels (0.5–1 ppbv) while trajectories originating in the HSC resulted in high HCHO (up to 31.5 ppbv). Based on the best multiparametric linear regression model fit, the HCHO levels at the MT site can be accounted for as follows: 38.5±12.3% from primary vehicular emissions (using CO as an index of vehicular emission), 24.1±17.7% formed photochemically (using peroxyacetic nitric anhydride (PAN) as an index of photochemical activity) and 8.9±11.2% from industrial emissions (using SO2 as an index of industrial emissions). The balance 28.5±12.7% constituted the residual which cannot be easily ascribed to the above categories and/or which is transported into the HGA. The CO related HCHO fraction is dominant during the morning rush hour (06:00–09:00 h, all times are given in CDT); on a carbon basis, HCHO emissions are up to 0.7% of the CO emissions. The SO2 related HCHO fraction is significant between 09:00–12:00 h. After 12:00 h HCHO is largely formed through secondary processes. The HCHO/PAN ratios are dependent on the SO2 levels. The SO2 related HCHO fraction at the downtown site originates in the ship channel. Aside from traffic-related primary HCHO emissions, HCHO of industrial origin serves as an appreciable source for OH in the morning.

Analysis of the isoprene chemistry observed during the New England Air Quality Study (NEAQS) 2002 intensive experiment

Isoprene and its first and second generation photochemical products, methyl vinyl ketone (MVK), methacrolein (MACR), and peroxymethacrylic nitric anhydride (MPAN), were measured off the coast of New England during the 2002 New England Air Quality Study (NEAQS) on board the NOAA Research Vessel Ronald H. Brown. The results of these measurements were analyzed using a simple sequential reaction model that has been used previously to examine regional oxidant chemistry. The highest isoprene impact was observed in air masses that had passed over an area of high isoprene emission WSW of Boston. The relative concentrations of isoprene and its first generation products show that the photochemistry is consistently “older” than the isoprene photochemistry observed at continental sites. The sequential reaction model was also applied to the aldehyde‐PANs (Peroxycarboxylic nitric anhydride) system, and the resulting PPN (peroxypropionic nitric anhydride)/propanal and PAN (peroxyacetic nitric anhydride)/acetaldehyde relationships were consistent with additional sources of PAN in this environment, e.g., isoprene photochemistry. This isoprene source was estimated to result in approximately 1.6 to 4 times more PAN in this environment relative to that produced from anthropogenic VOCs (volatile organic compounds) alone.

Measurement of the Henry's law coefficient and first order loss rate of PAN in n‐octanol

The Henry's Law solubility and first order loss rates of PAN (peroxyacetic nitric anhydride, CH3C(O)OONO2) in a model non‐polar solvent, n‐octanol, were measured for a range of temperatures pertinent to the lower troposphere (273–298 °K). The solubility was found to be factors of 6 to 12 higher than those measured previously for pure water, ranging between 110 ± 7.5 M/atm at 273°K and 34 ± 1.7 M/atm at 298°K. The loss rates were found to vary from below 0.5 × 10−5 sec−1 at 273°K to 5.2 ± 1.9 × 10−5 sec−1 at 298°K. Several simple approaches were used to estimate that the uptake of PAN on organic aerosol has a negligible impact on ambient PAN concentrations.

Measurement of peroxycarboxylic nitric anhydrides (PANs) during the ITCT 2K2 aircraft intensive experiment

Measurements of peroxycarboxylic nitric anhydrides (PANs), peroxyacetic nitric anhydride (CH3C(O)OONO2; PAN), and peroxypropionic nitric anhydride (CH3CH2C(O)OONO2; PPN) were made in the spring of 2002, off the west coast of North America, as part of the Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) project. Long‐range transport of Asian emissions was observed in which PAN and PPN mixing ratios were as high as 650 pptv and 90 pptv, respectively. Moreover, these two species constituted as much as 80% of the odd nitrogen (NOy) in those air masses, and median PAN/NOy was more than 60% at altitudes of 4 km and above. Systematic differences in the ratio of PPN to PAN were observed in air masses that had been impacted by Asian urban emissions relative to those impacted by biomass burning. Mixing ratios of PAN and PPN were also elevated in the marine boundary layer close to the west coast of California, possibly because of photochemical production driven by maritime NOx emissions.

Photochemistry in the arctic free troposphere: NOx budget and the role of odd nitrogen reservoir recycling

Abstract The budget of nitrogen oxides (NO x ) in the arctic free troposphere is calculated with a constrained photochemical box model using aircraft observations from the Tropospheric O 3 Production about the Spring Equinox (TOPSE) campaign between February and May. Peroxyacetic nitric anhydride (PAN) was observed to be the dominant odd nitrogen species (NO y ) in the arctic free troposphere and showed a pronounced seasonal increase in mixing ratio. When constrained to observed acetaldehyde (CH 3 CHO) mixing ratios, the box model calculates unrealistically large net NO x losses due to PAN formation (62 pptv/day for May, 1–3 km). Thus, given our current understanding of atmospheric chemistry, these results cast doubt on the robustness of the CH 3 CHO observations during TOPSE. When CH 3 CHO was calculated to steady state in the box model, the net NO x loss to PAN was of comparable magnitude to the net NO x loss to HNO 3 (NO 2 reaction with OH) for spring conditions. During the winter, net NO x loss due to N 2 O 5 hydrolysis dominates other NO x loss processes and is near saturation with respect to further increases in aerosol surface area concentration. NO x loss due to N 2 O 5 hydrolysis is sensitive to latitude and month due to changes in diurnal photolysis (sharp day–night transitions in winter to continuous sun in spring for the arctic). Near NO x sources, HNO 4 is a net sink for NO x ; however, for more aged air masses HNO 4 is a net source for NO x , largely countering the NO x loss to PAN, N 2 O 5 and HNO 3. Overall, HNO 4 chemistry impacts the timing of NO x decay and O 3 production; however, the cumulative impact on O 3 and NO x mixing ratios after a 20-day trajectory is minimal.

Ground‐based measurements of peroxycarboxylic nitric anhydrides (PANs) during the 1999 Southern Oxidants Study Nashville Intensive

Peroxycarboxylic nitric anhydrides (PANs) were measured at Cornelia Fort Airpark during the 1999 Nashville Intensive of the Southern Oxidants Study. The observed concentrations were similar to those measured in the 1994 and 1995 Nashville Intensives. The average daytime ratio of peroxypropionic nitric anhydride (PPN) to peroxyacetic nitric anhydride (PAN) was 13.7%. Extensive measurements were also made of peroxyisobutyric nitric anhydride (PiBN), which confirm the anthropogenic origin of this compound, and its ratio to PAN was 2.4% on average. The daytime ratio of peroxymethacrylic nitric anhydride (MPAN) to PAN was as high as 25% during periods of high biogenic hydrocarbon (BHC) impact. A simple linear combination model was used to estimate anthropogenic hydrocarbon (AHC) and BHC contributions to O3 production. On average, 80% of the O3 observed over 80 ppbv was attributed to AHC chemistry and 20% to BHC chemistry. An exception to this was a plume derived from a combination of power plant NOx and isoprene emissions from west of the city, in which the BHC contribution was at least 50 to 75%.

Application of a sequential reaction model to PANs and aldehyde measurements in two urban areas

Measurements of the peroxycarboxylic nitric anhydrides (PANs = peroxyacetic nitric anhydride, PAN, peroxypropionic anhydride, PPN, and peroxymethacrylic nitric anhydride, MPAN) and aldehydes (acetaldehyde, propanal, and methacrolein) were made at Nashville, TN. in 1999 and Houston, TX. in 2000. The data were interpreted with a sequential reaction model that included reaction of aldehydes with hydroxyl radical and formation or loss of PANs mediated by peroxyacyl radicals {RC(O)OO}. The comparison of the measured ratios with those predicted by the model showed a disagreement for PAN/acetaldehyde and PPN/propanal in Nashville, but agreement in Houston. The Nashville data set also showed a disagreement in the case of PAN/acetaldehyde and MPAN/methacrolein, but agreement for PPN/propanal and MPAN/methacrolein. These features were consistent with the relative importance of isoprene to PAN formation at each site. The ratios were found to be highly correlated with ozone mixing ratios at each site.

A method for the airborne measurement of PAN, PPN, and MPAN

An aircraft‐based instrument for the measurement of peroxyacetic nitric anhydride (PAN) and related compounds peroxypropionic nitric anhydride (PPN), and peroxymethacrylic nitric anhydride (MPAN) is described. The instrument functions by direct injection of a small sample (2 ambient cm2) into a wide bore fused silica capillary gas chromatographic separation column with subsequent detection by electron capture. The efficiency of separation and early elution of water made possible a sampling frequency of once every 5 min. The selective destruction of PAN type compounds at 125°C in actual ambient samples showed that no interfering species were present. Calibration of the instrument was accomplished by the total odd‐nitrogen (NOy) measurement of air mixtures of high‐purity PANs. Inflight calibrations of PAN in either thermally decomposed ambient air or dry zero air showed that the sensitivity of the instrument to PAN was not affected by other matrix species such as carbon dioxide or water. The instrument response to PPN and MPAN relative to that of PAN was consistent (within 5%) over the span of several months. The instrument response to PAN was linear up to 3.5 ppbv and the slope of the response versus [PAN] indicated a relative standard deviation of 2% over the course of a 30‐day field study. The detection limits of the method for PAN and PPN were estimated to be 5 pptv (3s) based on the uncertainty of peak detection. The overall accuracy of the PAN measurement was estimated to be ±(5 pptv+15%) in one campaign and ±(5 pptv+20%) in others.

A method for real‐time detection of PAN, PPN and MPAN in ambient air

A selected ion flow drift tube (SIFDT) apparatus and a proton transfer reaction mass spectrometer (PTR‐MS) were used to study the reactions of protonated water H3O+ and the proton bound water dimer (H2O)2H+ with PAN (peroxyacetic nitric anhydride, CH3C(O)OO NO2), PPN (peroxypropionic nitric anhydride, CH3CH2C (O)OONO2) and MPAN (peroxymethacrylic nitric anhydride, CH2C(CH3)C(O)OONO2). The protonated hydrates react rapidly with PAN, PPN and MPAN. Product ion peaks using ambient air as reactant gas could be unequivocally attributed to PAN, PPN and MPAN utilizing the thermal decomposition of these compounds on a hot surface. The results demonstrate that (H2O)nH+ (n=1,2) ions are excellent reagent ions for the real‐time detection of PAN and other organic nitrates in ambient air.

Ab Initio Study of Peroxyacetic Nitric Anhydride and Peroxyacetyl Radical: Characteristic Infrared Band of Peroxyacetyl Radical

The equilibrium geometries, the bond dissociation energies, harmonic vibrational frequencies, and infrared intensities of peroxyacetic nitric anhydride (PAN), peroxyacetyl radical (PA), and NO2 which are important species in environmental chemistry, have been studied using high level of ab initio calculations. The global minimum energy conformation of the PAN molecule is found to be s-cis-PAN. The predicted enthalpy and entropy changes at 1 atm and 298.15 K for the thermal decomposition of PAN are 25.8 kcal/mol and 42.3 cal/(mol·K), respectively. These values are in excellent agreement with the experimental values. A characteristic IR band of PAN appears at 1232 cm-1, which is a CH3 rocking mode coupled with CO and OO stretches. The corresponding band of the PA radical appears at 1216 cm-1, about 10 cm-1 lower than that of PAN. Thus, determining the concentrations of PAN based on only this band would not be so reliable. We find that the PA radical has a strong IR band at 1150 cm-1 due to the O−O stretch mode, while the PAN molecule has the corresponding band at 977 cm-1. Since PAN and the PA radical do not have other IR bands at this region, this characteristic band could be used for identification and measurement of the PA radical and thus for spectroscopic study of thermal decomposition mechanism of PAN.

Measurements of PAN, PPN, and MPAN made during the 1994 and 1995 Nashville Intensives of the Southern Oxidant Study: Implications for regional ozone production from biogenic hydrocarbons

Isoprene and a variety of other reactive hydrocarbons are released in large quantities by vegetation in forested regions and are thought to participate in the NOx‐catalyzed production of ozone, a serious air quality problem in North America and Europe [National Research Council, 1991]. The determination of the fraction of O3 formed from anthropogenic NOx and biogenic hydrocarbons (BHC) is a crucial step in the formulation of effective control strategies. Peroxymethacrylic nitric anhydride (MPAN, CH2C(CH3)C(O)OONO2) is formed almost entirely from the atmospheric oxidation of isoprene in the presence of NOx and is an excellent indicator of recent ozone production from isoprene and therefore biogenic hydrocarbons. Measurements are presented here of MPAN, peroxyacetic nitric anhydride (PAN, CH3C(O)OONO2), peroxypropionic nitric anhydride (PPN, CH3CH2C(O)OONO2) and ozone from separate data sets acquired during the 1994 and 1995 Nashville intensive studies of the Southern Oxidant Study. It was found that PAN, a general product of HC‐NOx photochemistry, could be well represented as a simple linear combination of contributions from BHC and anthropogenic hydrocarbon (AHC) chemistries as indicated by MPAN and PPN, respectively. The PAN:MPAN ratios found to be characteristic of BHC‐dominated chemistry ranged from 6 to 10. The PAN:PPN ratios found to be characteristic of AHC‐dominated chemistry ranged from 5.8 to 7.4. These BHC and AHC attributions were used to estimate the contributions of anthropogenic and biogenic hydrocarbons to regional tropospheric ozone production, and substantial BHC‐O3 (50–60 ppbv) was estimated in cases where high NOx from power plants was present in areas of high BHC emission. This estimation method provides direct evidence of significant photochemical ozone production from the oxidation of biogenic hydrocarbons in the presence of NOx.

Measurement of alkyl nitrates at Chebogue Point, Nova Scotia during the 1993 North Atlantic Regional Experiment (NARE) intensive

Measurements of six alkyl nitrates, methyl‐, ethyl‐, 1‐propyl‐, 2‐propyl‐, 2‐butyl, and 3‐pentyl nitrates, and two peroxycarboxylic nitric anhydrides, peroxyacetic nitric anhydride (PAN) and peroxypropionic nitric anhydride (PPN) were made at Chebogue Point, Nova Scotia, during the 1993 North Atlantic Regional Experiment campaign. The correlation of alkyl nitrates (RONO2) with carbon monoxide makes it clear that the chemistry at this site is being driven by continental emissions, since RONO2 compounds are known to be by‐products of HC‐NOx photochemistry. Comparison of the ratios of alkyl nitrates to their parent hydrocarbons to that of 2‐butyl nitrate/butane showed significant deviations from trends predicted from rate constants, branching ratios, and loss rates. For ethyl nitrate this deviation is likely due to a combination of many additional pathways to the intermediate peroxy radical from the decomposition of larger alkoxy radicals. The propyl nitrates showed trends that differed from one another; 2‐propyl nitrate was a factor of 2 to 3 higher than predicted, while 1‐propyl nitrate was a factor of 8 to 10 higher than predicted. The trend of 3‐pentyl nitrate/pentane was relatively close (about 50% lower) to the predicted trend. The relationship between PAN and PPN showed unexpectedly high ratios of PPN to PAN in air masses coming from the south and west of the site, implying a slight local source of PPN.

Regional ozone from biogenic hydrocarbons deduced from airborne measurements of PAN, PPN, and MPAN

NOx‐catalyzed production of ozone over large regions of North America and Europe is a serious air quality problem that often involves biogenic hydrocarbons, mainly isoprene. Peroxy‐methacrylic nitric anhydride (MPAN, CH2C(CH3)C(O)OONO2) is formed uniquely from isoprene‐NOx photochemistry hence is an indicator of recent ozone production from isoprene. Presented here are the first airborne measurements of MPAN along with PAN (peroxyacetic nitric anhydride, CH3C(O)OONO2), PPN (peroxypropionic nitric anhydride, CH3CH2C(O)OONO2) and ozone measurements. Relationships between these species are used to estimate the contributions of anthropogenic and biogenic hydrocarbons (BHC) to regional tropospheric ozone production, providing direct evidence of ozone production from BHC‐NOx photochemistry.

Relationships between PAN and ozone at sites in eastern North America

Measurements of ozone and PAN (peroxyacetic nitric anhydride) were made at four sites in eastern North America; Bondville, Illinois, Egbert, Ontario, Scotia, Pennsylvania, and Whitetop Mountain, Virginia., in July and August of 1988 as part of a study of regional oxidant photochemistry. The concentrations of PAN ranged from <0.010 to 9.2 parts‐per‐billion by volume (ppbv) and those of O3 ranged from <2 to 139 ppbv. Diurnal concentration profiles showed PAN and O3 to be removed within nocturnal boundary layers, especially if nitric oxide was present, and that O3 was, for most sites, more rapidly removed than PAN. The only mountain top site at which PAN was measured showed distinctly different diurnal profiles in which O3 was actually higher at night, suggesting that convective flow driven by surface cooling served to transport air down from higher in the mixed layer at night. The afternoon production of PAN and O3 was also apparent and led to an overall linear correlation of O3 and PAN between the hours of 1300 and 1800. The comparison of this result with other measurements, estimates of PAN formation rates, and model calculations indicates that the production of PAN relative to ozone is far greater (x3) than can be accounted for by acetaldehyde reactions with OH, there is a wide disparity in model descriptions of PAN production, and confirms the non‐linear dependence of O3 production on NOx.

Photodissociation of methyl nitrate in a molecular beam

The photodissociation of methyl nitrate, CH30N02, has been investigated by photofragment translational spectroscopy. At the photolysis wavelength of 193 nm the predominant primary decay (-70%) involves the fission of the weak CH3O-NO2 bond (Di - 41 kcal/mol) to yield CH3O + NO2 fragment pairs which show a bimodal translational energy distribution. The component consisting of the fast fragment pairs has an average translational energy (ET) = 41 kcal/mol and a recoil anistropy 6 = 0.9, while the slow component is characterized by (ET) = 19 kcal/mol and 0 = 0. A significant portion of the NO2 fragments of the slow component is subject to a unimolecular decay to NO + O(3P). An additional primary decay route leads to the formation of methyl nitrite, CH3ON0, and atomic oxygen O(lD) with (ET) = 6 kcal/mol and /3 = 1.2. This competing reaction requires fission of the strong N-0 bond (@,I - 118 kcal/mol) and its occurrence indicates an initial localization of the photoexcitation on the NO2 moiety in the parent molecule. At higher laser fluence secondary photodissociation of the primary fragments CH3ONO was observed. Photolysis at 248 nm is shown to produce CH30 + NO2 fragment pairs exclusively, with (ET) = 17 kcal/mol. Nitric oxide (NO) and nitrogen dioxide (NOz), collectively denoted as NO,, play a central role in the catalytic and photochemical processes of the atmo~phere.'-~ The most important precursor and product species of atmospheric NO, are nitric acid (HN03), nitrate ion (NOj) in aerosols, and peroxyacetic nitric anhydride (PAN). These compounds and NO, account for most of what is often referred to as reactive oddnitrogen, NO,. Recent atmospheric measurements3q4 indicate that in some cases 742% of the NO, consists of relatively stable organic species, most notably the alkyl nitrates RON02, R = CH3, CzH5, etc. These compounds are formed as minor products in the reaction of organic peroxy radicals with NO and are removed both by reaction with OH radicals and by photolysis with light in the near-UV region. The relative importance of the two destruction mechanisms depends on the atmospheric conditions and on the substituent group R, with the photolytic decay route being most important in the case of methyl nitrate, CH30N02.3 From this point of view the photodissociation mechanism of alkyl nitrates merits attention.

The thermal decomposition of peroxyacetic nitric anhydride (PAN) and peroxymethacrylic nitric anhydride (MPAN)

AbstractThe rate coefficients of thermal decomposition of peroxyacetic nitric anhydride (PAN) and peroxymethacrylic nitric anhydride (MPAN) were measured over the temperature range 302–323 K. The resulting Arrhenius expressions were k = 1017.4±0.4 exp(−28.5 ± 0.5/RT) for PAN, and k = 1016.2±0.7 exp(−26.8 ± 1.0/RT) for MPAN, where the activation energy is in Kcal/mol. These results are in good agreement with previous studies of PAN and other PAN‐type compounds, and imply that energies of RC(O)OONO2 bonds are relatively independent of the nature of R.

Contribution of organic nitrates to the total reactive nitrogen budget at a rural eastern U.S. site

Measurements of ambient levels of PAN (peroxyacetyl nitrate or, more properly, peroxyacetic nitric anhydride), C2–C5 alkyl nitrates, NOx (NO+NO2), HNO3, and NO3− particulates were made concurrently with a measurement of total reactive nitrogen species (NOy) at Scotia, Pennsylvania, from July 16 to August 31, 1988. Each of the organic nitrates exhibited a marked diurnal variation. The concentration of PAN varied from 0.05 to 3 ppbv (parts per billion by volume). The sum of the alkyl nitrate concentrations varied from less than 2 to 200 pptv (parts per trillion by volume). The NOy levels varied from 1 to 30 ppbv. During periods of high photochemical activity the contributions to NOy were 30–45% from HNO3, 20–25% from PAN, 15–25% from NOx, 5% from NO3−, and an additional 1.5% from the C2–C5 alkyl nitrates, on average. During these periods, about 15% of the measured NOy could not be accounted for by the sum of the individually measured species. The unidentified species that constitute this 15% exhibit behavior similar to that of the measured organic nitrates.

Capillary gas chromatographic separation of alkyl nitrates and peroxycarboxylic nitric anhydrides

The measurement of peroxycarboxylic nitric anhydrides (so-called PAN-type compounds) has become a crucial part of atmospheric chemical research. One such compound, peroxyacetic nitric anhydride (PAN), has been shown to comprise a large fraction of photochemically active nitrogen, which is often referred to as reactive odd-nitrogen (NO/sub y/). PAN, while originally discovered and measured by IR spectroscopy, is routinely measured by gas chromatography with electron capture detection (GC/ECD). The packed columns used for this analysis have changed little in the past 25 years and have consisted mainly of low-molecular-weight Carbowax liquid phases on deactivated solid supports. Alkyl nitrates (RONO/sub 2/) have emerged as another class of compounds likely to contribute to atmospheric NO/sub y/, and preliminary measurements of them have been made by capillary GC/ECD. The authors wish to report here preliminary studies on use of capillary gas chromatographic columns for the simultaneous analysis of both PAN-type compounds and alkyl nitrates in the presence of ambient atmospheric halogenated hydrocarbons. The goal of this research has been the development of a single method for the atmospheric measurement of PAN and peroxypropionic nitric anhydride (PPN), as well as alkyl nitrates in the size range C/sub 1/-C/sub 5/. Capillary columns are a logical choicemore » for such a method due to increased resolution and potentially shorter analysis times relative to packed columns.« less