Decomposition Of Peroxyacetyl Nitrate Research Articles

The seasonal cycle of peroxyacetyl nitrate (PAN) in the European Arctic

Measurements of peroxyacetyl nitrate (PAN) over a 3-yr period at the Zeppelin mountain near Ny-Ålesund, Svalbard show a distinct annual cycle with a spring maximum of about 400 pmol mol −1, and a summer minimum of 80 pmol mol −1. In this paper the measurement technique is shown together with a detailed error discussion. PAN at this high latitude location is co-transported with ozone. Thermal decomposition of PAN in the high Arctic troposphere may occur mostly during summer. During spring it is too small for PAN to have a sizeable local effect on the observed spring time ozone maximum.

On the origin of tropospheric ozone and NOx over the tropical South Pacific

The budgets of ozone and nitrogen oxides (NOx = NO + NO2) in the tropical South Pacific troposphere are analyzed by photochemical point modeling of aircraft observations at 0–12 km altitude from the Pacific Exploratory Mission‐Tropics A campaign flown in September‐October 1996. The model reproduces the observed NO2/NO concentration ratio to within 30% and has similar success in simulating observed concentrations of peroxides ( H2O2, CH3OOH), lending confidence in its use to investigate ozone chemistry. It is found that chemical production of ozone balances only half of chemical loss in the tropospheric column over the tropical South Pacific. The net loss is 1.8 × 1011 molecules cm−2 s−1. The missing source of ozone is matched by westerly transport of continental pollution into the region. Independent analysis of the regional ozone budget with a global three‐dimensional model corroborates the results from the point model and reveals the importance of biomass burning emissions in South America and Africa for the ozone budget over the tropical South Pacific. In this model, biomass burning increases average ozone concentrations by 7–8 ppbv throughout the troposphere. The NOx responsible for ozone production within the South Pacific troposphere below 4 km can be largely explained by decomposition of peroxyacetylnitrate ( PAN) transported into the region with biomass burning pollution at higher altitudes.

Measurements of NOx and PAN and estimates of O3 production over the seasons during Mauna Loa Observatory Photochemistry Experiment 2

Measurements of peroxyacetyl nitrate (PAN) and NOx and a variety of other constituents were made over approximately 1‐month‐long intensives in the autumn of 1991 and the winter, spring, and summer of 1992 during the second Mauna Loa Observatory Photochemistry Experiment (MLOPEX 2). PAN and NOx in the free troposphere had maximum abundances in spring in concert with the well‐known maximum in O3. The ratio of the spring to summer averages was a factor of 4.1 for PAN, a factor of 1.6 for O3, and only a factor of 1.4 for NOx. During most intensives, variations over periods of a few days to a week were often larger than the average seasonal amplitude. In free tropospheric air masses local to Hawaii, average PAN/NOx ratios were a maximum in winter through spring but in the range of 0.25–0.86 in all intensives. PAN decomposition is unlikely to be the major net source of NOx in local air masses in summer and fall. The low HNO3/NOx ratios determined during MLOPEX 1 were confirmed during MLOPEX 2. Intensive average ratios of 1.6–3.8 over the year are lower than some model predictions. Both the low ratio and the magnitude of NOx imply a shortcoming in our understanding of the transformations and sources of NOy constituents in the central Pacific, The 3‐ to 4‐km altitude region near Hawaii was a net importer of O3, on average, over the year. The average net rate of production of O3 in free tropospheric air was near zero in winter, −0.4 to −0.8 ppbv/d in spring, −1.4 ppbv/d in summer, and −0.6 ppbv/d in autumn. Thus the spring maximum in O3 is not due to local photochemistry. We believe, as has been concluded from the long‐term measurements of long‐lived constituents by the Climate Monitoring and Diagnostics Laboratory, that the variation of ozone precursors over the year and on shorter timescales of a few days to a week is controlled predominantly by changes in long‐range transport: more frequent sampling of higher‐latitude and higher‐altitude air masses in winter and spring versus more frequent sampling of well‐aged air from lower altitudes and latitudes in summer and autumn.

Effects of Chemical Mechanism Uncertainties on the Reactivity Quantification of Volatile Organic Compounds Using a Three-Dimensional Air Quality Model

Accurate quantification of the ozone-forming potential, termed reactivity, of volatile organic compounds (VOCs) is critical for correctly assessing the impacts of emissions on air quality. As reactivity-based regulations are being more carefully considered for urban ozone control strategies, the uncertainties in the ability to quantify reactivity are gaining importance. This study utilized a three-dimensional air quality model to examine the uncertainty in reactivity quantification resulting from a set of reaction rate constant uncertainties. A previous study identified the set of rate constants that were most critical for single-cell model ozone predictions. With the detailed airshed model, uncertainties in rate constants for aldehyde photolysis, nitric acid formation, and decomposition of peroxy acetyl nitrate (PAN) and peroxy propionyl nitrate plus higher PAN analogues (PPN) exhibited the greatest impact on relative compound reactivity values. For the compounds and reactions examined, the combined responses to 2σ changes in reaction rate constants were approximately 15% of the predicted relative reactivity values, with the reactivities of ethylbenzene and toluene exhibiting the greatest response. The choice of reactivity quantification measures and the air quality models used had a greater impact on relative reactivity predictions than did the rate constant uncertainties.

Reactive nitrogen and its correlation with O3 and CO over the Pacific in winter and early spring

Measurements of NO, NOy, O3, and CO were made during NASA's Global Tropospheric Experiment/Pacific Exploratory Mission‐West B (GTE/PEM‐West B) carried out over the western Pacific in February and March 1994. NOx was calculated from NO using a photostationary state model ((NOx)mc). Correlations between these species are presented, and some insights into the sources of NOx and NOy are described. The boundaries between the lower, middle, and upper troposphere have been defined at potential temperatures of 311 K and 328 K, which correspond to the geometric altitudes of about 5 and 9 km at 30°N. Enhancements in the mixing ratios of NOy and CO were observed in the lower and middle troposphere. A positive correlation was found between these two species suggesting that the high NOy values were due to anthropogenic emissions over the continental surface. On the other hand, O3 increased little with increase in CO. As a result, NOy/O3 ratios were higher in air more influenced by pollution. NOy values in 55 and 28% of the air masses sampled in the lower and middle troposphere, respectively, were higher than the clean free tropospheric NOy‐O3 range when O3 values simultaneously observed were used. High (NOx)mc/NOy ratios between 0.15 and 0.3 were found in the boundary layer with relatively low mixing ratios of CO and NOy during the three flights. These air masses were transported from a higher altitude (∼5 km) and a higher latitude (∼50°N) within a few days. The peroxyacetyl nitrate (PAN)/NOy ratios were generally high (∼0.4) in these air masses, and the thermal decomposition of PAN was a probable source of NOx. In the middle troposphere the (NOx)mc mixing ratio did not generally increase with NOy or CO, suggesting that the transport of air masses affected by anthropogenic emissions did not increase the NOx level significantly. In the upper troposphere, very minor effects from the continental surface sources were seen in the CO mixing ratio. By contrast, NOy values in 33% of the air masses were higher than those expected when stratospheric air intrusion is assumed to be a single source of NOy based on NOy‐O3 correlation analyses. This result suggests significant free tropospheric NOy sources, namely exhaust from the aircraft and NO production by lightning activity. In fact, spikes in the (NOx)mc mixing ratios were observed near the aircraft corridor south of Tokyo at an altitude of 10 km. These two free tropospheric NOx sources were considered to be important in determining the levels of the upper tropospheric NOx and NOy during PEM‐West B.

Effect of peroxy radical reactions on the predicted concentrations of ozone, nitrogenous compounds, and radicals

The reactions of organic peroxy radicals with NO, HO2, organic peroxy radicals, and NO3 along with the formation and decomposition of peroxyacetyl nitrate are all important for the modeling of atmospheric chemistry. Recent laboratory measurements of the rate constants for peroxy radical‐peroxy radical reactions show that there are large differences between these rate constants. We present methods of estimating organic peroxy radical self‐reaction rate constants from an empirical expression. These self‐reaction rate constants may be used to estimate the rates of peroxy radical cross reactions. There are also new data available on the rate constants for peroxyacetyl nitrate formation, decomposition, the reaction of acetyl peroxy radicals and other organic peroxy radicals with NO, and the reactions of NO3 with organic peroxy radicals. To estimate the importance of these reactions, these new data along with revisions to the product yields for organic peroxy radical‐organic peroxy radical reactions were implemented in the mechanism of Stockwell et al. [1990]. The revised mechanism yields significantly different concentrations of peroxyacetyl nitrate, higher organic hydroperoxides and peroxyacetic acid concentrations. Nighttime concentrations of organic peroxy radicals, HO2, HO, and NO3 are also strongly affected by organic peroxy radical‐organic peroxy radical reactions and the reactions of organic peroxy radicals with NO3. Our results suggest that the reactions of organic peroxy radicals with NO3 are more important than organic peroxy radical‐organic peroxy radical reactions in the nighttime atmosphere.

The effect of acetyl peroxy-peroxy radical reactions on peroxyacetyl nitrate and ozone concentrations

Recent field studies have shown that peroxyacetyl nitrate (PAN) decomposes faster than ozone at night even when the ratio of [NO 2] to [NO] is high. PAN is important because it is a reservoir of nitrogen dioxide and peroxy radicals. Nighttime PAN decomposition results from the loss of acetyl peroxy radical through either reaction with nitric oxide or peroxy radical-peroxy radical (R0 2- RO 2) reactions. Peroxy radical-peroxy radical reactions have a strong effect on PAN concentrations and the atmospheric odd nitrogen balance under conditions of low nitric oxide concentrations. Box model simulations, counter species analysis and sensitivity analysis were used to determine the relative importance of the reactions of acetyl peroxy radical with nitric oxide, hydroperoxy radical, acetyl peroxy radical (self-reaction), methyl peroxy radical and other peroxy radicals and the effect of these reactions on PAN concentrations. The base simulation conditions were typical of an aged NO x containing plume mixing with rural air containing non-methane hydrocarbon (NMHC) which is typical of cities in the southern United States and Canada. This sensitivity analysis shows that the self-reaction of acetyl peroxy radical and its reaction with methyl peroxy radical are especially important at night. The self-reaction of acetyl peroxy radical is a significant nighttime sink of acetyl peroxy radical, PAN and a nighttime source of methyl peroxy radical. These RO 2RO 2 reactions are shown to be important for the modeling of nighttime PAN concentrations.

Origin of tropospheric NOx over subarctic eastern Canada in summer

The origin of NOx in the summertime troposphere over subarctic eastern Canada is investigated by photochemical modeling of aircraft and ground‐based measurements from the Arctic Boundary Layer Expedition (ABLE 3B). It is found that decomposition of peroxyacetyl nitrate (PAN) can account for most of the NOx observed between the surface and 6.2 km altitude (aircraft ceiling). Forest fires represent the principal source of PAN in the region, implying the same origin for NOx. There is, however, evidence for an unidentified source of NOx in occasional air masses subsiding from the upper troposphere. Isoprene emissions from boreal forests maintain high NOx concentrations in the continental boundary layer over eastern Canada by scavenging OH and NO3, thus slowing down conversion of NOx to HNO3, both in the daytime and at night. This effect is partly compensated by the production of CH3CO3 radicals during isoprene oxidation, which slows down the decomposition of PAN subsiding from the free troposphere. The peroxy radical concentrations estimated from concurrent measurements of NO and NO2 concentrations during ABLE 3B are consistent with values computed from our photochemical model below 4 km, but model values are low at higher altitudes. The discrepancy may reflect either a missing radical source in the model or interferences in the NO2 measurement.

Promotion of the Oxidation of Nitric Oxide and Hydrocarbon by the Thermal Decomposition of Peroxyacetyl Nitrate (PAN) at Night

Abstract The decomposition of PAN in the presence of nitric oxide and propene in the air was investigated at 30 °C under dark conditions. The number of nitric oxide molecules oxidized per each PAN molecule decomposed varied from 3.7 to above 5 with increase of the ratio of initial concentration of propene to that of nitric oxide.

The seasonal cycle of nitrogen oxides in the Arctic troposphere at Barrow, Alaska

Ground level concentrations of total reactive nitrogen (NOy) and NO in the Arctic troposphere were measured at the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory site at Barrow, Alaska, from March–November, 1990. After screening out impacts from local and regional pollution sources, a well‐defined seasonal cycle of background NOy concentrations is apparent. Concentrations of 560–620 parts per thousand by volume (pptv) during early spring decayed sharply during April and May to extremely low summertime values (median 70 pptv). NO concentrations were < 8 pptv during most background measurements. However, a pulse of NO to ∼35 pptv (maximum hourly average) occurred coincidentally with the NOy decay. Decomposition of peroxyacetyl nitrate (PAN) (and perhaps other reservoir NOy species) due to increasing temperatures and/or insolation in late spring may have caused this NO pulse. Furthermore, by converting NOy from a stable reservoir species (PAN) to a more reactive form (NOx), PAN decomposition is believed to have contributed to the observed NOy decay through formation and deposition of HNO3. Through this process of NOx release in response to warming temperatures, the springtime Arctic NOy reservoir may affect springtime O3 levels both in the Arctic and in the northern mid‐latitudes. During summer, higher NOy and NO concentrations were observed during periods of flow off the inland tundra as compared to marine flow periods, suggesting greater vertical mixing over land. Synoptic flow patterns and diurnal changes had minimal effects on background NOy concentrations. NOy and O3 concentrations were positively correlated during summer, possibly indicating long‐range transport of both and/or the presence of a midtropospheric NOy reservoir combined with a stratospheric O3 source. The data presented and discussed here are compared to the results of modeling studies reporting NOy concentration predictions for the Arctic. Current models have been unable to adequately simulate NOy concentrations and speciation in the Arctic.

Thermal decomposition pathways for peroxyacetyl nitrate (PAN): Implications for atmospheric methyl nitrate levels

The unimolecular decomposition pathways of peroxyacetyl nitrate (PAN) have been investigated in the presence of added NO 2 over the temperature range 298–345 K. The major products of the PAN decomposition were CO 2 and, depending on the ratio of O 2 to NO 2 in the experiment, either CH 2O or methyl nitrate. From the observed PAN decay rates and product yields, upper limits for the direct formation of either NO 3 or methyl nitrate from the unimolecular decay of PAN were obtained. The results indicate that these channels occur with rate constants that are thousands of times slower than dissociation of PAN into peroxyacetyl and NO 2, and that PAN decomposition is not a significant source of atmospheric methyl nitrate.

Heterogeneous transformation of peroxyacetylnitrate

The heterogeneous decomposition of peroxyacetylnitrate (PAN) has been investigated using a flow reactor and infrared spectroscopic analysis. The decomposition rate in air due to glass surfaces follows the relation d[PAN]/d t = − S/ V([PAN] × 7 × 10 7 + [CH 3C(O)OO] × 5 × 90 12)exp(−9382/ T) molecules cm −3 s −1 ( S/ V=surface to volume ratio). The rate observed for NH 4HSO 4-covered surfaces is lower than in the glass case. The rate is high enough to affect many laboratory experiments but too slow to have any influence on PAN decomposition under ambient conditions.

Summertime photochemistry of the troposphere at high northern latitudes

The budgets of O3, NOx (NO+NO2), reactive nitrogen (NOy), and acetic acid in the 0–6 km column over western Alaska in summer are examined by photochemical modeling of aircraft and ground‐based measurements from the Arctic Boundary Layer Expedition (ABLE 3A). It is found that concentrations of O3 in the region are regulated mainly by input from the stratosphere, and losses of comparable magnitude from photochemistry and deposition. The concentrations of NOx (10–50 ppt) are sufficiently high to slow down O3 photochemical loss appreciably relative to a NOx‐free atmosphere; if no NOx were present, the lifetime of O3 in the 0–6 km column would decrease from 46 to 26 days because of faster photochemical loss. The small amounts of NOx present in the Arctic troposphere have thus a major impact on the regional O3 budget. Decomposition of peroxyacetyl nitrate (PAN) can account for most of the NOx below 4‐km altitude, but for only 20% at 6‐km altitude. Decomposition of other organic nitrates might supply the missing source of NOx. The lifetime of NOy, in the ABLE 3A flight region is estimated at 29 days, implying that organic nitrate precursors of NOx could be supplied from distant sources including fossil fuel combustion at northern mid‐latitudes. Biomass fire plumes sampled during ABLE 3A were only marginally enriched in O3; this observation is attributed in part to low NOx emissions in the fires, and in part to rapid conversion of NOx to PAN promoted by low atmospheric temperatures. It appears that fires make little contribution to the regional O3 budget. Only 30% of the acetic acid concentrations measured during ABLE 3A can be accounted for by reactions of CH3CO3 with HO2 and CH3O2. There remains a major unidentified source of acetic acid in the atmosphere.

Atmospheric peroxyacetyl nitrate measurements over the Brazilian Amazon Basin during the wet season: Relationships with nitrogen oxides and ozone

Aircraft measurements of peroxyacetyl nitrate (PAN) were performed for the first time over the Brazilian Amazon Basin during the wet season (April–May 1987) as part of the NASA Atmospheric Boundary Layer Experiment (ABLE 2B) expedition. In addition to tropical measurements, free tropospheric latitudinal profiles were also obtained during transit flights to and from Manaus, Brazil. Complementing PAN were measurements of NO, O3, CO, C2Cl4, radon, and a variety of other chemical and meteorological parameters. Over the Amazon Basin, PAN was present at a mixing ratio of 5 to 125 ppt. Despite strong local and regional convective activity, a distinct vertical structure with highest mixing ratios aloft was observed. Median PAN mixing ratios of 12, 20, and 48 ppt were present in the 0‐ to 2‐, 2‐ to 4‐, and 4‐ to 6‐km height intervals, respectively. Data collected during the cross‐basin flights showed that the PAN mixing ratio was highest over the rain forest and declined eastward toward the Atlantic Ocean. Over the Atlantic, PAN was low and appeared to be uniformly distributed with height. Above the Amazon forest, PAN was as much as 5 times more abundant than NOx with the largest PAN/NOx ratios occurring at the highest altitudes. Both PAN and possibly the PAN/NOx ratio showed a latitudinal dependence, with decreasing values from the northern midlatitudes to the tropics. Free tropospheric (4–6 km) PAN mixing ratios were found to be strongly correlated with those of O3. Preliminary modeling results indicate that a sizeable fraction of NOx and HNO3 in the free troposphere could result from PAN decomposition alone. The primary source of free tropospheric PAN observed over the Amazon Basin is not well understood. Large‐scale transport from the upper tropospheric PAN reservoir present at the higher northern latitudes, and precursor emissions of nonmethane hydrocarbons from the forest and NOx from soil and lightning clearly play an important role.

Budgets of reactive nitrogen, hydrocarbons, and ozone over the Amazon forest during the wet season

The atmospheric composition over the Amazon forest during the wet season is simulated with a onedimensional photochemical model for the planetary boundary layer (PBL) extending from the ground to 2000‐m altitude. The model is constrained and evaluated using observations from the ABLE 2B field expedition. Results indicate that only ≈ 20% of NOx emitted by soils is exported to the atmosphere above the forest canopy. The balance is deposited to vegetation before leaving the canopy layer. The small NOx flux that escapes from the canopy is nevertheless sufficient to account for the low NO concentrations observed in the PBL. Decomposition of peroxyacetylnitrate (PAN) supplied from aloft provides only a minor source of NOx in the PBL, although it could provide the major source of NOx at higher altitudes. Soil emission can account for only a portion of NOy observed over the forest. Organic nitrates of nonbiogenic origin likely account for the balance of NOy. Enhancements of CO observed in the PBL cannot be explained by oxidation of biogenic hydrocarbons, and appear to reflect direct emission of CO by the forest ecosystem. Concentrations of O3 in the PBL are regulated largely by transport from aloft and deposition to the canopy, with little net influence from photochemistry. Ozone is photochemically produced immediately above the forest where NO concentrations are relatively high, but is photochemically consumed in the upper portion of the PBL.

Decomposition of peroxyacetyl nitrate and peroxypropionyl nitrate during gas chromatographic determination with a wide-bore capillary and two packed columns

Analyse des composes du titre par chromatographie en phase gazeuse. Etude des colonnes (Chromosorb B et Chromosorb W), des phases stationnaires (Carbowax 400 et QF-1 + diglycerol) des conditions operatoires

植物実験用ＰＡＮ暴露装置の試作

Peroxyacetyl nitrate (PAN) exposure system for plants was produced and its efficiency was studied. Gaseous PAN was prepared by bubbling air into dilute PAN solution which was synthesized by the method of Gaffney et al.. PAN concentration in the exposure air was controlled uniformly for 6-8 hours by changing flow rate of bubbling air, although PAN concentration in the exposure box decayed by the rate of about 0.05%/min. By refrigerating bubbler to 0°C, PAN decomposition in the solution was restrained and vaporization of solvent into the exposure air was also minimized. The effect of temperature and relative humidity on PAN stability in the exposure box was also investigated. PAN concentration in the box was analyzed by electron capture detection gas chromatograph (ECD-GC), of which traceability was established by way of calibration by long path Fourier transform infrared spectrometer (FT-IR).

Fourier transform infrared spectroscopic study of the thermal stability of peroxyacetyl nitrate

The unimolecular decomposition of peroxyacetyl nitrate (PAN) to form methyl nitrate and carbon dioxide has been studied over the temperature range 298-338 K by Fourier transform infrared spectroscopy (FTIR). Pure PAN samples (> 98%; 2-30 torr) were found to decompose thermally, nearly quantitatively, to these products, with the only other observed product being nitromethane (< 10%). Both PAN decomposition and methyl nitrate formation rates yielded the Arrhenius equation, k = (2.1 x 10/sup 12/) exp(-24.800 +/- 1800 cal/(K mol/RT)) s/sup -1/. Perdeuterio-PAN was synthesized and observed to decompose to perdeuteriomethyl nitrate and carbon dioxide with no apparent isotope effect. One pathway is a concerted reaction most likely proceeding via a cyclic intermediate, and the other previously identified equilibrium between PAN and the peroxyacetyl radical and nitrogen dioxide. The rate of the PAN decomposition in a large excess of NO was determined to be 2.2 x 10/sup -4/ s/sup -1/ at 298 K. This rate is somewhat slower than previously reported for this pathway. The results are discussed with respect to the atmospheric lifetime of PAN and the potential atmospheric production of methyl nitrate. 24 references, 3 figures, 4 tables.

The effect of temperature on ozone formation in the propene/nitrogen dioxide/air system

Abstract A series of laboratory experiments were conducted to determine whether the positive correlation observed in the ambient atmosphere between ozone and temperature could, in part, be due to a temperature dependency of the photochemical smog reaction kinetics. The experiments were conducted using the propene/NO2/air system in General Motors Research Laboratories’ dynamic irradiation chamber. Over the range of temperatures investigated, 10°C to 50°C, the maximum observed ozone concentration increased with increasing temperature from 10°C to 40°C. Between 40°C and 50°C there was no further increase in ozone. In contrast, it was observed that the amount of peroxyacetylnitrate formed decreased with increasing temperature. These observations can be attributed to the temperature dependence of the thermal decomposition of peroxyacetylnitrate. At low temperatures, the increased stability of this compound makes it a sink for nitrogen dioxide; conversely, at higher temperatures, peroxyacetylnitrate is too unst...