Atmospheric measurements of peroxyacetylnitrate (PAN) in rural, south-east England: Seasonal variations winter photochemistry and long-range transport

The atmospheric fate of ethyl and neopentyl nitrates: ·OH-oxidation mechanism, kinetic property, and environmental impacts

Organic nitrate (RONO2) is an important component of secondary organic aerosol. Ethyl nitrate (EN) and neopentyl nitrate (NN) are prototypical RONO2 with high atmospheric concentrations, but their fate remains unclear. Herein, the ·OH-initiated degradation mechanism and kinetics of EN and NN were investigated using quantum chemical calculations and kinetics modeling. The environmental persistence of EN and NN was evaluated by calculating atmospheric lifetimes. Unexpectedly, the aqueous water has an inhibitory effect on the degradation of reactants by increasing the Gibbs-free barrier, and the air-water interfaces could accelerate EN transformation into CH3CHO. Notably, the subsequent evolution process of C-center radicals can form polyfunctional oxygenated organic pollutants, aldehydes, and peroxyacyl nitrates in the presence of ·OH, O2, HOx, and NOx. The toxicological assessment showed that EN and NN had harmful effects on ecosystems. This work provides a deeper theoretical insight into the atmospheric fate and influence of RONO2.

Characteristics and sources of peroxyacetyl nitrate (PAN) in the rural North China Plain: Results from 1-year continuous observations

Peroxyacetyl nitrate (PAN) is an important photochemical pollutant in the troposphere, whereas long-term measurements are scarce in rural areas in North China Plain (NCP), resulting in unclear seasonal variations and sources of PAN in rural NCP. In this study, we conducted a 1-year observation of PAN during 2021-2022 at the rural NCP site. The average concentrations of PAN were 1.10, 0.75, 0.65, and 0.88 ppbv in spring, summer, autumn, and winter, respectively, with a 1-year average of 0.81 ± 0.60 ppbv. Calculations indicate that the loss of PAN through thermal decomposition in summer accounts for 43.2% of the total formed PAN, which is an important reason for the low concentration of PAN in summer. We speculate that since the correlation between PAN and O3 in winter is significantly lower than that in other seasons, the observed regional transport of PAN cannot be ignored in winter. Through budget analysis, regional transport accounted for 12.8% and 55.9% of the observed PAN on the spring and winter pollution days, respectively, which showed that regional transport played key roles during the photochemical pollution of the rural NCP in winter. The potential source contribution function revealed that the transported PAN mainly comes from southern Hebei in spring. In winter, the transported PAN was mainly from Langfang, Hengshui, and southern Beijing. Our findings may aid in understanding PAN variations in different seasons in rural areas and highlight the impact of regional transport on the PAN budget.

Peroxyacetyl nitrate (PAN) in the urban atmosphere

Peroxyacetyl nitrate (PAN) in air has been well known as the indicator of photochemical smog due to its frequent occurrences in Seoul metropolitan area. This study was implemented to assess the distribution characteristics of atmospheric PAN in association with relevant parameters measured concurrently. During a full year period in 2011, PAN was continuously measured at hourly intervals at two monitoring sites, Gwang Jin (GJ) and Gang Seo (GS) in the megacity of Seoul, South Korea. The annual mean concentrations of PAN during the study period were 0.64±0.49 and 0.57±0.46 ppb, respectively. The seasonal trends of PAN generally exhibited dual peaks in both early spring and fall, regardless of sites. Their diurnal trends were fairly comparable to each other. There was a slight time lag (e.g., 1 h) in the peak occurrence pattern between O3 and PAN, as the latter trended to peak after the maximum UV irradiance period (16:00 (GJ) and 17:00 (GS)). The concentrations of PAN generally exhibited strong correlations with particulates. The results of this study suggest that PAN concentrations were affected sensitively by atmospheric stability, the wet deposition of NO2, wind direction, and other factors.

Observations of H2O2 and PAN in a rural atmosphere

Measurements of gaseous H2O2 and peroxyacetyl nitrate (PAN) concentrations in air are given for a site in rural southern England over an approximately 4-year period. In both cases the data show both diurnal and seasonal patterns. Temperature and wind direction had clear influences on the recorded concentrations of both species. There was an indication of increasing H2O2 concentrations with time. The use of a two-dimensional global model confirmed that this would be expected to occur alongside growth in ozone formation. It is suggested that, during photochemical episodes, the sequential build-up of ozone, PAN and H2O2 could be important in influencing the ability of vegetation to resist the effects of aggressive pollutants.