Measurements of peroxyacetyl nitrate (pan) and peroxypropionyl nitrate (ppn) at selected urban, rural and remote sites

Improved continuous measurement system for atmospheric total peroxy and total organic nitrate under the high NOx condition

We improved the thermal dissociation cavity attenuated phase shift spectroscopy (TD-CAPS) instrument to measure atmospheric total peroxy nitrates (PNs) and organic nitrates (ONs) continuously under the condition of high NOx. In TD-CAPS, PNs and ONs are dissociated in heated quartz tubes to form NO2, and the NO2 concentration is measured by cavity attenuated phase shift spectroscopy (CAPS). The original TD-CAPS system overestimates PN and ON concentrations in the presence of high NO concentrations. Our laboratory experiments and numerical simulations showed that the main cause of the overestimation was NO oxidation to NO2 by peroxy radicals generated in the heated quartz tubes. In the improved system, NO was converted to NO2 by adding excess O3 after the quartz tubes so that CAPS detected NOx (NO and NO2) instead of NO2. The uncertainty of the improved system was less than 20% with ∼15 parts per billion by volume (ppbv) NO and ∼80 ppbv NO2. The estimated detection limit (3σ) was 0.018 ppbv with an integration time of 2 min in the presence of 64 ppbv NO2. The improved system was tested for measurement of PNs and ONs in an urban area, and the results indicated that interference from NO was successfully suppressed.

Evolution of surface ozone pollution pattern in eastern China and its relationship with different intensity heatwaves

With climate warming, eastern China has experienced a significant increase in temperature accompanied by intensified ozone pollution. We aimed to investigate the spatiotemporal patterns and relationships between ozone levels and temperature in eastern China using observation-based ozone data from 418 air quality monitoring stations and temperature data from ERA5. The summer maximum temperature and annual ozone concentration in eastern China increased significantly between 2015 and 2022, with increases rate of 10% and 2.84 μg/m3 yr-1, respectively. The baseline ozone concentration was increasing over time. The average difference in MDA8 O3 concentration in spring, summer, and autumn decreased, with more ozone pollution spreading into spring and autumn, indicating a trend of prolonging the ozone season. During the June-July-August (JJA) period of 2015-2022, heatwaves increased significantly in eastern China. The frequency of heatwave events >10 days played a vital role in exacerbating ozone pollution. During the JJA period, the increase rate in MDA8 O3 concentration was 9.31 μg/m3 yr-1 during heatwave periods, significantly higher than that during non-heatwave periods (4.01 μg/m3 yr-1). The correlation between MDA8 O3 concentration and temperature was as high as 0.99, indicating that temperature was vital in ozone formation during the JJA period in eastern China. This study suggests that more stringent actions are needed to control ozone-precursor compounds during frequent summertime heatwaves in eastern China.

The abundance and inter-relationship of atmospheric peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), O3, and NOy during the wintertime in Beijing, China

Although atmospheric peroxyacetyl nitrate (PAN) and O₃ have been extensively measured in Beijing during the summertime, the abundances of PAN, peroxypropionyl nitrate (PPN) and the total odd-reactive nitrogen budget (NO_y) and their inter-relationship have been studied comparatively less in the winter. Here we measured atmospheric PAN, PPN, O₃, NO_x, and NO_y in Beijing from Nov. 2012 to Jan. 2013. Compared with our previous results in the summertime, much lower levels were observed in the winter, with the mean and maximum values of 311.8 and 1465 pptv for PAN, 52.8 and 850.6 pptv for PPN, and 11.6 and 36.7 ppbv for O₃. In contrast, high levels were found as 94.2 and 374.9 ppbv for NO_y, with a major constituent of NO_x (75.9%). The source to the west and northwest made the significant contribution to the relatively high O₃ concentrations during nighttime. PAN concentrations were highly related with the PAN-rich air mass transported from the southeast during the nighttime, whereas predominated by local photochemical production during the daylight. The distributions of NO_x and NO_y were dominated by local emission and photochemical production during daylight but also influenced by air masses transported from south direction during nighttime. Significant positive correlation (R² = 0.9, p < 0.0001) between PAN and PPN with a slope (∆PPN/∆PAN) of 0.17 indicated that anthropogenic volatile organic compounds (AVOCs) dominated the photochemical formation of PANs in Beijing, and the independent relationship between the PPN/PAN ratio and PAN (>500 pptv) implied a steady state between PAN and PPN achieving rapidly in the polluted air masses. Negative correlation and slopes between PAN and O₃ likely resulted from their weak photochemical productions in the winter, coupled with the large NO sources which acted as a local sink for O₃, but much less so for PAN due to its enhanced thermal stability under low temperature.

A modeling study of the peroxyacetyl nitrate (PAN) during a wintertime haze event in Beijing, China

Peroxyacetyl nitrate (PAN), as the second most important photochemical pollutant, could threaten human health and terrestrial ecosystem. Observed high PAN concentrations in wintertime in Beijing are comparable to those in summertime when photochemistry is strong. In this study, we investigated the variations of concentrations of PAN and other related chemical species during a haze event on February 13-16, 2017 in Beijing using a combination of in-situ observations and the WRF-Chem model simulation. During this episode, the observed mean (maximum) PAN concentrations at the urban and rural sites were 1.9 (4.7) ppb and 1.8 (4.3) ppb, respectively. Model evaluation showed that the simulation with CBM-Z gas-phase scheme performed much better than simulation using the RADM2 scheme, which mainly results from the accurate representation of the reaction rates for PAN formation through CH₃C(O)O₂ radicals and NO₂ in the CBM-Z scheme_. But simulated PAN concentrations in Beijing were still underpredicted using the CBM-Z scheme, likely due to the underestimation of VOC emissions. Since the lifetime of PAN becomes as long as several days in wintertime due to lower temperature, it could be conducive to be accumulated and transported. Sensitivity simulation demonstrated that local sources accounted for about 15%-30% of mean PAN concentrations over most of Beijing during the event, lower than that of PM_2.5 (25%-60%). These suggest that during Beijing wintertime polluted days, increased PAN concentration, which is dominantly contributed by regional transport from surrounding areas, will cause more health concerns, and its control strategies need larger regional efforts than those conducted for PM_2.5.

Thermal dissociation cavity attenuated phase shift spectroscopy for continuous measurement of total peroxy and organic nitrates in the clean atmosphere

A thermal dissociation cavity attenuated phase shift spectroscopy (TD-CAPS) instrument was developed for measuring total peroxy nitrates (PNs) and organic nitrates (ONs) concentrations in the clean atmosphere. This instrument is easy to operate and can be applied to continuous measurement of PNs and ONs. A continuously measurable system is convenient to perform observations, especially in remote areas. Three lines (NO2, PNs, and ONs lines) were used for thermal dissociation. The NO2 line contains a quartz tube that is not heated, while the PN and ON lines contain quartz tubes that are heated at 433 K and 633 K, respectively. The concentrations of NO2, NO2 + PNs, and NO2 + PNs + ONs can be obtained from the NO2, PN, and ON lines, respectively. The lower limit values of the detection limit (3σ) for PNs and ONs were estimated to be 21 parts per trillion by volume with an integration time of 2 min. PNs were selectively thermally decomposed in the PNs line and formed NO2 quantitatively. In the ONs line, both PNs and ONs were thermally decomposed to produce NO2 quantitatively, but partial decomposition of HNO3 at 633 K interfered with the ONs measurement. Therefore, a HNO3 scrubber is required before the ONs line. Continuous observations were conducted with the TD-CAPS instrument in a remote area, and the instrument performed well for obtaining PNs and ONs concentrations.

Wintertime peroxyacetyl nitrate (PAN) in the megacity Beijing: role of photochemical and meteorological processes

Previous measurements of peroxyacetyl nitrate (PAN) in Asian megacities were scarce and mainly conducted for relative short periods in summer. Here, we present and analyze the measurements of PAN, O3, NO(x), etc., made at an urban site (CMA) in Beijing from 25 January to 22 March 2010. The hourly concentration of PAN averaged 0.70 x 10(-9) mol/mol (0.23 x 10(-9) -3.51 x 10(-9) mol/mol) and was well correlated with that of NO2 but not O3, indicating that the variations of the winter concentrations of PAN and 03 in urban Beijing are decoupled with each other. Wind conditions and transport of air masses exert very significant impacts on O3, PAN, and other species. Air masses arriving at the site originated either from the boundary layer over the highly polluted N-S-W sector or from the free troposphere over the W-N sector. The descending free-tropospheric air was rich in O3, with an average PAN/O3 ratio smaller than 0.031, while the boundary layer air over the polluted sector contained higher levels of PAN and primary pollutants, with an average PAN/O3 ratio of 0.11. These facts related with transport conditions can well explain the observed PAN-O3 decoupling. Photochemical production is important to PAN in the winter over Beijing. The concentration of the peroxyacetyl (PA) radical was estimated to be in the range of 0.0014 x 10(-12) -0.0042 x 10(-12) mol/mol. The contributions of the formation reaction and thermal decomposition to PAN's variation were calculated and found to be significant even in the colder period in air over Beijing, with the production exceeding the decomposition.

Mutagenicity in lung of big Blue((R)) mice and induction of tandem-base substitutions in Salmonella by the air pollutant peroxyacetyl nitrate (PAN): predicted formation of intrastrand cross-links

Peroxyacetyl nitrate (PAN) is a ubiquitous air pollutant formed from NO(2) reacting with acetoxy radicals generated from ambient aldehydes in the presence of sunlight and ozone. It contributes to eye irritation associated with photochemical smog and is present in most urban air. PAN was generated in a chamber containing open petri dishes of Salmonella TA100 (gas-phase exposure). After subtraction of the background mutation spectrum, the spectrum of PAN-induced mutants selected at 3.1-fold above the background mutant yield was 59% GC-->TA, 29% GC-->AT, 2% GC-->CG, and 10% multiple mutations - primarily GG-->TT tandem-base substitutions. Using computational molecular modeling methods, a mechanism was developed for producing this unusual tandem-base substitution. The mechanism depends on the protonation of PAN near the polyanionic DNA to release NO(2)(+) resulting in intrastrand dimer formation. Insertion of AA opposite the dimerized GG would account for the tandem GG-->TT transversions. Nose-only exposure of Big Blue((R)) mice to PAN at 78ppm (near the MTD) was mutagenic at the lacI gene in the lung (mutant frequency +/-S.E. of 6.16+/-0.58/10(5) for controls versus 8.24+/-0.30/10(5) for PAN, P=0.016). No tandem-base mutations were detected among the 40 lacI mutants sequenced. Dosimetry with 3H-PAN showed that 24h after exposure, 3.9% of the radiolabel was in the nasal tissue, and only 0.3% was in the lung. However, based on the molecular modeling considerations, the labeled portion of the molecule would not have been expected to have been bound covalently to DNA. Our results indicate that PAN is weakly mutagenic in the lungs of mice and in Salmonella and that PAN produces a unique signature mutation (a tandem GG-->TT transversion) in Salmonella that is likely due to a GG intrastrand cross-link. Thus, PAN may pose a mutagenic and possible carcinogenic risk to humans, especially at the high concentrations at which it is present in some urban environments.

Nitrogen deposition in California forests: a review

Atmospheric concentrations and deposition of the major nitrogenous (N) compounds and their biological effects in California forests are reviewed. Climatic characteristics of California are summarized in light of their effects on pollutant accumulation and transport. Over large areas of the state dry deposition is of greater magnitude than wet deposition due to the arid climate. However, fog deposition can also be significant in areas where seasonal fogs and N pollution sources coincide. The dominance of dry deposition is magnified in airsheds with frequent temperature inversions such as occur in the Los Angeles Air Basin. Most of the deposition in such areas occurs in summer as a result of surface deposition of nitric acid vapor (HNO3) as well as particulate nitrate (NO3-) and ammonium (NH4+). Internal uptake of gaseous N pollutants such as nitrogen dioxide (NO2), nitric oxide (NO), HNO3, peroxyacetyl nitrate (PAN), ammonia (NH3), and others provides additional N to forests. However, summer drought and subsequent lower stomatal conductance of plants tend to limit plant utilization of gaseous N. Nitrogen deposition is much greater than S deposition in California. In locations close to photochemical smog source areas, concentrations of oxidized forms of N (NO2, HNO3, PAN) dominate, while in areas near agricultural activities the importance of reduced N forms (NH3, NH4+) significantly increases. Little data from California forests are available for most of the gaseous N pollutants. Total inorganic N deposition in the most highly-exposed forests in the Los Angeles Air Basin may be as high as 25-45 kg ha(-1) year(-1). Nitrogen deposition in these highly-exposed areas has led to N saturation of chaparral and mixed conifer stands. In N saturated forests high concentrations of NO3- are found in streamwater, soil solution, and in foliage. Nitric oxide emissions from soil and foliar N:P ratios are also high in N saturated sites. Further research is needed to determine the ecological effects of chronic N deposition, and to develop appropriate management options for protecting water quality and managing plant nutrient resources in ecosystems which no longer retain excess N.

Cytogenetic analyses of the in vitro and in vivo responses of murine cells to peroxyacetyl nitrate (PAN)

Peroxyacetyl nitrate (PAN) is one of a class of common air pollutant formed by the action of sunlight on volatile organic compounds and nitrogen oxides. PAN has been shown to be a bacterial mutagen. To determine if PAN can cause DNA damage in mammalian cells, we exposed murine peripheral blood lymphocytes (PBLs) to various volumes of PAN in vitro and analyzed the cells for chromosome aberrations (CAs), sister chromatid exchanges (SCEs), and DNA damage using the single cell gel (SCG) assay. At in vitro concentrations of PAN that were cytotoxic (inhibited cell division), an increase in DNA damage was noted in the SCG assay. At lower exposure levels that permitted cell division, no increases in SCEs, CAs, or DNA damage were evident. For in vivo studies, male mice were exposed nose-only by inhalation for 1 h to 0, 15, 39 or 78 ppm PAN, and their lung cells removed and cultured for the scoring of SCEs and CAs. In addition, PBLs and lung cells were analyzed by the SCG assay. No dose-related effects were found in any of the assays. These data indicate that PAN does not appear to be a potent clastogen or DNA damaging agent in mammalian cells in vivo or in vitro.

Mutagenicity of peroxyacetyl nitrate (PAN) in vivo: tests for somatic mutations and chromosomal aberrations

A series of experiments was conducted in which Chinese hamsters inhaled PAN, an ubiquitous pollutant that is present in the atmosphere at concentrations that are as high as, or higher than, other known genotoxic agents. The animals were exposed to PAN in air at concentrations of approximately 3 ppm for up to 1 month and then examined for somatic mutations and chromosomal aberrations. Mutations were assayed by measuring the frequency of thioguanine-resistant lung fibroblasts (isolated de novo and cultured). Chromosomal aberrations were assayed by measuring the frequency of micronuclei in either the bone marrow (polychromatic erythrocytes) or the lungs (binucleate lung fibroblasts cultured in the presence of cytochalasin B). The results for the test animals were compared to those from animals exposed similarly, but without PAN. Although in each experiment the mutation frequencies for the test animals were higher than the corresponding controls, the mutation frequencies were not significantly different from the concurrent negative controls (P > .05) or the historical controls, except for experiment C. In experiment C, there was a significant regression of mutation frequency versus dose (P < 0.001) if all of the historical controls for pooled animals are included at zero dose. No reproducible evidence of chromosomal breakage was found in either lung or bone marrow. Thus, although PAN has been found to be a bacterial mutagen, we did not find statistically significant evidence of mutagenicity in vivo. The toxicity of PAN limited the exposure concentration that could be used. When all of the PAN data were used, the best estimate of the mutagenic potency proved to be comparable to that of ethylene dibromide, a carcinogenic atmospheric pollutant.