Peroxyacetyl Nitrate Research Articles

Molecular Compositions, Mutagenicity, and Mutation Spectra of Atmospheric Oxidation Products of Alkenes and Dienes Initiated by NOx + UV or Ozone: A Structure-Activity Analysis.

Photooxidation products resulting from volatile organic compounds (VOCs) reacting with sunlight are important contributors to gas-phase air pollution. We characterized the product-weighted mutagenic potencies (rev m3 mgC-1 h-1) in Salmonella TA100 of atmospheres resulting from the hydroxyl radical (OH)-initiated photochemical oxidation of 11 C4 or C5 alkenes or dienes in the presence of nitric oxide (NO) and from the ozonolysis of four VOCs without NO (isoprene; 1,3-pentadiene; 1,4-pentadiene; and 1,3-butadiene). Irradiated atmospheres from precursors with a single C═C bond (3-methyl-1-butene, 2-methyl-1-butene, cis/trans-2-pentene, 2-methyl-2-butene, 1-butene, and 1-pentene) had low potencies (<5), whereas linear dienes with terminal C═C bonds had high potencies (50-65). Dienes with a branched structure (isoprene) or internal C═C bonds (1,3-pentadiene) had intermediate potencies (15-20). No VOCs were mutagenic without photochemical oxidation. VOCs+O3 in the dark produced less mutagenic atmospheres than photochemistry in the presence of NO. Atmospheres induced primarily C to T and C to A mutations, the main base substitutions in nonsmoker lung cancer. Atmospheres from the photooxidation of isoprene and 1,3-pentadiene also induced GG to TT, the signature mutation of peroxyacetyl nitrate. Five molecular compositions identified by Chemical Ionization Mass Spectrometry (CIMS), most containing nitrogen, correlated (r = 0.76-0.85) with the mutagenic potencies of irradiated atmospheres; most had a likely nitrate functional group. Assessment of the mutagenicity of emitted VOCs should consider VOC photooxidation products, especially dienes with terminal C═C bonds, as these products likely contribute to overall health effects from ambient air pollution.

Monthly Characteristics and Source–Receptor Relationships of Anthropogenic Total Nitrate in Northeast Asia

The complex nonlinear characteristics of atmospheric chemistry necessitate the development of new methods for calculating source–receptor (S–R) relationships for secondary air pollutants. In this study, the monthly characteristics and S–R relationships of anthropogenic total nitrate (i.e., the sum of N from nitric acid, inorganic nitrate, and peroxyacetyl nitrate) in Northeast Asia were simulated and analyzed. The Community Multiscale Air Quality (CMAQ), Fifth-Generation NCAR/Penn State Mesoscale (MM5), and Sparse Matrix Operator Kernel Emissions (SMOKE) models were employed for air quality modeling, meteorological fields, and emissions processing, respectively. The study area encompassed Republic of Korea, Japan, and most of China. Five source/receptor regions were defined to derive the S–R relationships: three in China, one in Republic of Korea, and one in Japan. To produce data for the calculation of the S–R relationship, several experiments were conducted with a 20% reduction in NOx emission sources. As a result of the S–R relationships, China was rarely impacted by the other two countries. The total depositions in other countries were significantly dominated by China (i.e., 43.5% and 40.7% in Republic of Korea and Japan, respectively, and up to 82.3% in December for Republic of Korea).

Exploring the long-term variations and high concentration episodes of peroxyacetyl nitrate in Megacity Seoul

Over the past few years, peroxyacetyl nitrate (PAN) has drawn significant attention as a key indicator of photochemical pollution owing to its intimate relationship with ozone and associated health effects. This study presents measurements conducted at the Korea University campus in Seoul during the high-ozone seasons from 2018 to 2021. PAN concentration was measured using fast gas chromatography with luminol chemiluminescence detection (GC-LCD), alongside measurements of O3, volatile organic compounds (VOCs), NO, NO2, and meteorological variables, including boundary layer height (BLH).The mean concentrations of PAN and O3 over the years were 0.56 ppbv and 35 ppbv in 2018, 1.29 ppbv and 58 ppbv in 2019, 0.21 ppbv and 50 ppbv 2020, and 0.53 ppbv and 46 ppbv in 2021, respectively. The annual variation observed in Seoul is consistent with trends seen in major cities worldwide during the COVID19 pandemic, reflecting a substantial reduction in urban emissions. Notably, the mean concentration of NOx and VOCs decreased significantly by more than 50 % and 25%, respectively, from 2019 to 2021.At temperatures above 30 °C, PAN decomposition was accelerated, decoupling a consistent positive relationship between PAN and O3 in 2020 and 2021. The results of a 0-D photochemical model (F0AM) calculation demonstrated that PAN formation primarily stems from anthropogenic VOCs, particularly > C2 alkenes. Elevated PAN concentrations during nighttime were attributed to boundary layer expansion and upper-air entrainment. Instances where PAN concentrations surged to at least 3 ppbv or higher in 2019 were attributed to biomass burning impacted air, as evidenced by concurrent elevations in K+ and OC in PM2.5, and O3.This study underscores the complex interplay of factors influencing PAN and ozone enhancements under decreased precursor levels, with an emphasis on dynamic change in the boundary layer, and long-distance transport of non-fossil sources during agricultural burning seasons.

Trends of peroxyacetyl nitrate and its impact on ozone over 2018–2022 in urban atmosphere

Peroxyacetyl nitrate (PAN) is an important photochemical product and affects ozone (O3) formation in the troposphere. Yet, the long-term observation of PAN remains scarce, limiting the full understanding of its impacts on photochemical pollution. Here, we observed PAN from 2018 to 2022 in urban Fuzhou, Southeastern China. We found that, in contrast to upward trend of O3, PAN concentrations shown a significant decreasing trend at an average rate of −0.07 ppb/year. NO2, CO, UVB, and T contributed to the decreasing trend of PAN according to Machine learning analyses, while the effect of O3-represented atmospheric oxidation capacity on PAN was fluctuating from year to year. Chemical box model revealed active PA production and depletion in Fuzhou. Thus, despite the decreasing PAN concentration, PAN chemistry effectively promoted O3 formation by rising ROx levels, leading to increases of 2.18%–58.4% in net O3 production rate in different years. Our results provide valuable insights into the evolution of photochemical pollution in urban environments.

Reactive Nitrogen Partitioning Enhances the Contribution of Canadian Wildfire Plumes to US Ozone Air Quality

AbstractQuantifying the variable impacts of wildfire smoke on ozone air quality is challenging. Here we use airborne measurements from the 2018 Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE‐CAN) to parameterize emissions of reactive nitrogen (NOy) from wildfires into peroxyacetyl nitrate (PAN; 37%), NO3− (27%), and NO (36%) in a global chemistry‐climate model with 13 km spatial resolution over the contiguous US. The NOy partitioning, compared with emitting all NOy as NO, reduces model ozone bias in near‐fire smoke plumes sampled by the aircraft and enhances ozone downwind by 5–10 ppbv when Canadian smoke plumes travel to Washington, Utah, Colorado, and Texas. Using multi‐platform observations, we identify the smoke‐influenced days with daily maximum 8‐hr average (MDA8) ozone of 70–88 ppbv in Kennewick, Salt Lake City, Denver and Dallas. On these days, wildfire smoke enhanced MDA8 ozone by 5–25 ppbv, through ozone produced remotely during plume transport and locally via interactions of smoke plume with urban emissions.

Measured and Modeled Trends of Seven Tropospheric Pollutants in the High Arctic From 1999 to 2022

AbstractThe long‐term trends and seasonality of many tropospheric pollutants are not well characterized in the high Arctic due to a dearth of trace‐gas measurements in this remote region. In this study, the inter‐ and intra‐annual variabilities of carbon monoxide (CO), acetylene (C2H2), ethane (C2H6), methanol (CH3OH), formaldehyde (H2CO), formic acid (HCOOH), and peroxyacetyl nitrate (PAN) in the high Arctic region were derived from the total column time‐series of ground‐based Fourier transform infrared (FTIR) measurements at Eureka, Nunavut (80.05°N, 86.42°W, 2006–2020) and Thule, Greenland (76.53°N, 68.74°W, 1999–2022). Consistent seasonal cycles were observed in the FTIR measurements at both sites for all species. Negative trends were observed for CO, C2H2, and CH3OH at both sites, and for HCOOH at Eureka. Positive trends were detected for C2H6 and H2CO at both sites, and for PAN at Eureka. Additionally, a 19‐year simulation was performed using the novel GEOS‐Chem High Performance model v14.1.1 for the period of 2003–2021. The model was able to reproduce the observed seasonality of all gases, but all species showed negative biases relative to observations, and CH3OH was found to have a particularly large bias of approximately −70% relative to the FTIR measurements. The GEOS‐Chem modeled trends broadly agreed with observations for all species except C2H6, H2CO, and PAN, which were found to have opposite trends in the model. For some species, the measurement‐model differences are suspected to be the result of errors or underestimations in the emissions inventories used in the simulation.

Complexities of peroxyacetyl nitrate photochemistry and its control strategies in contrasting environments in the Pearl River Delta region

Peroxyacetyl nitrate (PAN) is a hazardous secondary pollutant and a nitrogen reservoir in the troposphere, while comprehensive studies on its spatiotemporal distribution, chemical sources, and control strategies are limited. This study addressed these issues based on 1-year multi-site observations in the Pearl River Delta region, showing a pattern of higher PAN levels in the cold season, particularly in coastal areas. Moreover, in situ modeling indicated a net photochemical PAN formation in the warm season, while PAN was dominated by regional transport in the cold season (i.e., rural and coastal areas), releasing NO2 and PA radicals and promoting ozone (O3) formation. In addition, the feasibility of joint control of PAN and O3 was confirmed by their isopleth diagrams. C7–C9 aromatics and C4–C5 alkenes, largely from vehicle exhaust and solvent usage, were identified as the predominant contributors to PAN formation in this region. Overall, this study deepens our understanding of PAN chemistry and provides valuable insights into its control measures.

Impact of aerosol actinic radiative effect on ozone during haze pollution in the Pearl River Delta region

Large amounts of aerosol in the atmosphere can cause significant attenuation of photochemical radiation and have a substantial impact on ozone and other secondary pollutants involved in photochemical reactions. This study examines the impact of aerosol actinic radiative effect on ozone and secondary pollutants during typical haze processes in the Pearl River Delta (PRD) region. The investigation employed lidar data and Weather Research Forecast–Community Multiscale Air Quality (WRF-CMAQ) modeling system. The results revealed that the aerosol caused a significant decrease in ground-level photolysis rates of NO2 and ozone by 22% and 29%, respectively, when haze pollution was severe. The actinic radiative effect of aerosol caused an average reduction of more than 10 ppb in ground level ozone concentration in the PRD, with the core area experiencing a maximum reduction of 30 ppb. Additionally, the core area witnessed a maximum reduction of 2 ppb in peroxyacetyl nitrate (PAN) and 2 μg/m3 in PM2.5. Due to reduced photolysis rates, nitrogen oxides increased by more than 5 ppb on average, reaching up to 10 ppb, while volatile organic compounds (VOCs) increased by a maximum of 10 ppb in the core region. Temporally, the aerosol actinic radiative effect was most pronounced in the morning and less significant in the afternoon.

Transpacific Transport of Asian Peroxyacetyl Nitrate (PAN) Observed from Satellite: Implications for Ozone.

Peroxyacetyl nitrate (PAN) is produced in the atmosphere by photochemical oxidation of non-methane volatile organic compounds in the presence of nitrogen oxides (NOx), and it can be transported over long distances at cold temperatures before decomposing thermally to release NOx in the remote troposphere. It is both a tracer and a precursor for transpacific ozone pollution transported from East Asia to North America. Here, we directly demonstrate this transport with PAN satellite observations from the infrared atmospheric sounding interferometer (IASI). We reprocess the IASI PAN retrievals by replacing the constant prior vertical profile with vertical shape factors from the GEOS-Chem model that capture the contrasting shapes observed from aircraft over South Korea (KORUS-AQ) and the North Pacific (ATom). The reprocessed IASI PAN observations show maximum transpacific transport of East Asian pollution in spring, with events over the Northeast Pacific offshore from the Western US associated in GEOS-Chem with elevated ozone in the lower free troposphere. However, these events increase surface ozone in the US by less than 1 ppbv because the East Asian pollution mainly remains offshore as it circulates the Pacific High.

Sensitivity of atmospheric peroxyacetyl nitrate (PAN) formation and its impact on ozone pollution in a coastal city

Peroxyacetyl nitrate (PAN) ranks among the troposphere's most prevalent organic peroxy radicals, and the photochemical production and loss pathways of PAN are mainly related to the generation and consumption of PA radicals. PA radicals can affect the atmospheric O3 generation by competing or providing precursors and affecting the atmospheric radical cycling. Field measurements took place at two sites in Shenzhen: the suburban site of Yangmeikeng Station (YMK) from September to October 2018, and the urban site of University town of Shenzhen (DXC) from September to October 2019. The average PAN levels of YMK and DXC were 0.57 and 0.87 ppb, which were similar to PAN concentrations in other southeastern coastal regions and lower than those in inland and northern regions in China. The model simulations showed that except PAN thermal decomposition, acetaldehyde (40.7% and 24.9%), other OVOCs (40.0% and 59.2%) and radical cycling (19.3% and 16.0%) were the major production pathways peroxyacetyl (PA) radicals at YMK and DXC. During the sampling period, the production of PAN resulted in a decreasing of local O3 generation at YMK (5.32 ± 3.2 ppb) and DXC (3.53 ± 12.21 ppb). The findings could make us more comprehensively understand the mechanism of atmospheric formation of PAN in urban and suburban sites in Shenzhen and its influence on the process of atmospheric photochemical reaction in Shenzhen.

Peroxyacetyl nitrate can be used as a comprehensive indicator of air pollution complex

With the acceleration of air cleaning activities in China, air pollution has entered a new stage characterized by seasonal interplay and predominance of fine particulate matter (PM2.5) and ozone (O3) pollutants. However, the differing peak seasons of these two pollution preclude the use of a unified indicator for air pollution complex. Given that peroxyacetyl nitrate (PAN) originates from secondary formation and persists under low-temperature conditions for extended periods, it is vital to determine whether its concentration can be used as an indicator to represent air pollution, not only in summer but also in winter. Here, PAN observational data from 2018 to 2022 for Beijing were analyzed. The results showed that during photochemical pollution events in summer, secondary formation of PAN was intense and highly correlated with O3 (R = 0.8), while during PM2.5 pollution events in winter, when the lifetime of PAN is extended due to the low temperature, the PAN concentration was highly consistent with the PM2.5 concentration (R = 0.9). As a result, the PAN concentration essentially exhibited consistency with both the seasonal trends in the exceedance of air pollution (R = 0.6) and the air quality index (R = 0.8). When the daily average concentration exceeds 0.5 and 0.9 ppb, the PAN concentration can be used as a complementary indicator of the occurrence of primary and secondary standard pollution, respectively. This study demonstrated the unique role of PAN as an indicator of air pollution complex, highlighting the comprehensive ability for air quality characterization and reducing the burden of atmospheric environment management.

Underappreciated Emission Spikes From Power Plants During Heatwaves Observed From Space: Case Studies in India and China

AbstractThe frequency, intensity, and duration of extreme heatwaves are projected to increase in the global context of climate change. However, evidence of how anthropogenic emissions respond to heatwaves and further impact air quality remains elusive. Here, we use satellite remote sensing measurements alongside chemical transport model simulations to reveal abrupt variations in primary and secondary air pollutants introduced by extreme heatwaves. We highlight evidence from China and India, where satellite sulfur dioxide (SO2) and nitrogen dioxide (NO2) columns over thermal power plants enhance consistently responding to heatwaves. We attribute such spiked emissions to soaring electricity use and demonstrate that bottom‐up inventories underestimate the emissions from the power sector by 34.9% for the selected case. Elevated emissions facilitate fine particulate matter (PM2.5) and ozone (O3) formation over thermal power plants in an inhomogeneous manner, due to the combined effect of atmospheric oxidizing capacity, thermal decomposition of peroxyacetyl nitrate, planetary boundary layer rise, and air stagnation. Our results underscore the emerging challenge of pollution control attributable to the increasing climate penalty and the necessity of targeted control strategies and alternative energy sources during heatwaves.

On the influence of vertical mixing, boundary layer schemes, and temporal emission profiles on tropospheric NO2 in WRF-Chem – comparisons to in situ, satellite, and MAX-DOAS observations

Abstract. We present WRF-Chem simulations over central Europe with a spatial resolution of 3 km × 3 km and focus on nitrogen dioxide (NO2). A regional emission inventory issued by the German Environmental Agency, with a spatial resolution of 1 km × 1 km, is used as input. We demonstrate by comparison of five different model setups that significant improvements in model accuracy can be achieved by choosing the appropriate boundary layer scheme, increasing vertical mixing strength, and/or tuning the temporal modulation of the emission data (“temporal profiles”) driving the model. The model setup with improved vertical mixing is shown to produce the best results. Simulated NO2 surface concentrations are compared to measurements from a total of 275 in situ measurement stations in Germany, where the model was able to reproduce average noontime NO2 concentrations with a bias of ca. −3 % and R=0.74. The best agreement is achieved when correcting for the presumed NOy cross sensitivity of the molybdenum-based in situ measurements by computing an NOy correction factor from modelled peroxyacetyl nitrate (PAN) and nitric acid (HNO3) mixing ratios. A comparison between modelled NO2 vertical column densities (VCDs) and satellite observations from TROPOMI (TROPOspheric Monitoring Instrument) is conducted with averaging kernels taken into account. Simulations and satellite observations are shown to agree with a bias of +5.5 % and R=0.87 for monthly means. Lastly, simulated NO2 concentration profiles are compared to noontime NO2 profiles obtained from multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements at five locations in Europe. For stations within Germany, average biases of −25.3 % to +12.0 % were obtained. Outside of Germany, where lower-resolution emission data were used, biases of up to +50.7 % were observed. Overall, the study demonstrates the high sensitivity of modelled NO2 to the mixing processes in the boundary layer and the diurnal distribution of emissions.

Pollution characteristics of peroxyacetyl nitrate in karst areas in Southwest China

In recent years, the issue of photochemical pollution in the Guangxi region of China has escalated considerably. However, there remains a notable dearth of related research in this area. Peroxyacetyl nitrate (PAN), recognized as a reliable indicator of photochemical pollution, was the focus of our study. This study marks the inaugural observation of PAN levels in Guilin, a renowned world tourist destination situated in a typical karst region, during 1–31 October 2021. Throughout this observation period, the average volume concentration of PAN ranged from 0.087 to 2.559 ppb, which was 3.61 times higher than the South China background site of the Nanling. Combined with meteorological factors and potential source analysis, the causes of a typical high-value PAN process were explored during 24–29 October. The results showed that, during this high-value PAN event, pollution primarily originated from the horizontal transport of polluted air masses and the descent of high-altitude air masses from Hunan Province in the northeast direction. Additionally, the meteorological conditions, including high temperatures, intense radiation, and low humidity, fostered local PAN formation. Notably, traffic emissions emerged as the primary source of PAN's locally generated precursor volatile organic compounds. Furthermore, we estimated the background concentration of O3 to be approximately 20.347 ppb based on PAN monitoring data, constituting 44.4% of the total O3 levels in Guilin City. This study offers valuable insights for addressing and mitigating photochemical pollution in southern Chinese cities, while providing a theoretical foundation for regional pollution control efforts.摘要桂林是世界著名的地处喀斯特地区的旅游胜地, 其光化学污染问题日益严重.过氧乙酰硝酸酯(PAN)被认为是光化学污染的可靠指标, 也是本研究的重点. 本研究于2021年10月首次观测了桂林的PAN的浓度为0.087–2.559 ppb, 同时探讨了PAN典型高值过程的成因. 此次污染主要来源于东北方向污染气团的水平和高空输送, 同时, 高温, 强辐射和低湿度等气象条件也促进了本地PAN的形成. 本研究同时估算了桂林市的O3背景浓度为20.347 ppb.这项研究为城市的光化学污染控制工作提供了理论基础.

Observations of ozone, acyl peroxy nitrates, and their precursors during summer 2019 at Carlsbad Caverns National Park, New Mexico

ABSTRACT Carlsbad Caverns National Park (CAVE) is located in southeastern New Mexico and is adjacent to the Permian Basin, one of the most productive oil and natural gas (O&G) production regions in the United States. Since 2018, ozone (O3) at CAVE has frequently exceeded the 70 ppbv 8-hour National Ambient Air Quality Standard. We examine the influence of regional emissions on O3 formation using observations of O3, nitrogen oxides (NOx = NO + NO2), a suite of volatile organic compounds (VOCs), peroxyacetyl nitrate (PAN), and peroxypropionyl nitrate (PPN). Elevated O3 and its precursors are observed when the wind is from the southeast, the direction of the Permian Basin. We identify 13 days during the July 25 to September 5, 2019 study period when the maximum daily 8-hour average (MDA8) O3 exceeded 65 ppbv; MDA8 O3 exceeded 70 ppbv on 5 of these days. The results of a positive matrix factorization (PMF) analysis are used to identify and attribute source contributions of VOCs and NOx. On days when the winds are from the southeast, there are larger contributions from factors associated with primary O&G emissions; and, on high O3 days, there is more contribution from factors associated with secondary photochemical processing of O&G emissions. The observed ratio of VOCs to NOx is consistently high throughout the study period, consistent with NOx-limited O3 production. Finally, all high O3 days coincide with elevated acyl peroxy nitrate abundances with PPN to PAN ratios > 0.15 ppbv ppbv−1 indicating that anthropogenic VOC precursors, and often alkanes specifically, dominate the photochemistry. Implications: The results above strongly indicate NOx-sensitive photochemistry at Carlsbad Caverns National Park indicating that reductions in NOx emissions should drive reductions in O3. However, the NOx-sensitivity is largely driven by emissions of NOx into a VOC-rich environment, and a high PPN:PAN ratio and its relationship to O3 indicate substantial influence from alkanes in the regional photochemistry. Thus, simultaneous reductions in emissions of NOx and non-methane VOCs from the oil and gas sector should be considered for reducing O3 at Carlsbad Caverns National Park. Reductions in non-methane VOCs will have the added benefit of reducing formation of other secondary pollutants and air toxics.

Seasonal discrepancies and inter-relationship of peroxyacetyl nitrate (PAN), ozone, and other environmental factors in Hangzhou, East China

Peroxyacetyl nitrate (PAN, CH3C(O)OONO2) and ozone (O3) are both important photochemical products, both of which are detrimental to air quality, human health and ecosystem. In this study, we measured atmospheric PAN, O3 and other pollutants in Hangzhou during the whole 2021 year. Observed results revealed that the average concentrations of PAN and O3 during the whole observation period were 1.59 and 27.09 ppbv, respectively. PAN concentrations declined from the weekday to weekend, while O3 presented the reverse pattern. The abundance of PAN and O3 showed different variations in all seasons. Serious photochemical pollution in spring and autumn were featured by higher PAN levels (mean of 1.74 and 1.66 ppbv); whereas those in summer and spring were characterized by higher O3 levels (mean of 32.34 and 30.98 ppbv). With the extremely higher PAN/O3 ratio of 0.10, the results suggested the high-level photochemical pollution in Hangzhou. In all seasons, the diurnal peak of PAN appeared earliest in summer could be associated with rapid decomposition rate of PAN at noon with higher temperatures. The correlation between PAN and other factors varies across all seasons due to the environmental conditions are unique in each season. Through analysis of conditional probability function (CPF) and toluene/benzene ratio, traffic sources were identified as the main factor contributing to high PAN and O3 accumulation at a regional scale. Furthermore, backward trajectory analysis revealed that marine air masses affected the air of the monitoring site in both summer and autumn; whereas continental air masses impacted it in both spring and winter. This study provides novel insights into photochemical pollution process in a coastal city, eastern China.

A comprehensive observation on the pollution characteristics of peroxyacetyl nitrate (PAN) in Beijing, China

Peroxyacetyl nitrate (PAN) is a typical secondary photochemical product in the atmospheric environment with significant adverse effects on human health and plant growth. In this study, PAN and other pollutants, as well as meteorological conditions were observed intensively from August to September in 2022 at a typical urban sampling site in Beijing, China. The mean and maximum PAN concentrations during the observation period were 1.00 ± 0.97 ppb and 4.84 ppb, respectively. Severe photochemical pollution occurred during the observation period, with the mean PAN concentration about 3.1 times higher than that during the clean period. There was a good positive correlation between O3 and PAN, and their correlation was higher during the O3 exposure period than that during the clean period. The simulated results by box-model coupled with the Master Chemical Mechanism (MCM v3.3.1) showed that the O3-related reactions were the largest sources of OH radicals during O3 exposure period, which was conducive to the co-contamination of PAN and O3. Acetaldehyde (CH3CHO) and methylglyoxal (MGLY) were the largest OVOCs precursors of peroxyacetyl radicals (PA), with the contributions to the total PA generated by OVOCs about 67 % – 83 % and 17 % – 30 %, respectively. The reduction of emissions from liquefied petroleum gas (LPG) and solvent usage has the highest reduction effect on PAN and O3, followed by the control of gasoline vehicle exhaust emissions. This study deepens the understanding of the PAN photochemistry in urban areas with high O3 background conditions and the impact of anthropogenic activities on the photochemical pollution. Meanwhile, the findings of this study highlight the necessity of strengthening anthropogenic emissions control to effectively reduce the co-contamination of PAN and O3 in Beijing in the future.

Assessment of atmospheric levels of carbonyls in an urban environment of Argentina

It is well-documented that carbonyl compounds have adverse effects on human health. On the other hand, these oxygenated volatile organic compounds (OVOCs) are precursors of secondary pollutants such as tropospheric ozone or peroxy acetyl nitrate (PAN). In particular, formaldehyde, the simplest carbonyl, is the most abundant carbonyl in the air generated from the degradation of most volatile organic compounds (VOCs). This work presents for the first time the characterization and determination of levels of carbonyl compounds by passive monitoring performed from April–December 2021 in the city of Córdoba, Argentina, the second most populated Mediterranean city located in the center of the country. Annual concentrations, considering the 11 carbonyls measured, were in the range of 0.13–8.75 μgm−3. Formaldehyde and acetaldehyde were the carbonyls detected in the highest annual average concentrations of 4.44 ± 1.75 μgm−3 and 3.85 ± 1.44 μgm−3, respectively. These carbonyls represent a contribution of around 40–57% on total carbonyls measured. Statistical analysis to determine significant differences and Pearson correlations with the meteorological parameters were performed. Spring and summer were found to be the seasons with the highest carbonyl concentration linked to forest fire episodes, especially in springtime. The values for the C1/C2 and C2/C3 ratios showed that sources of carbonyl formation are anthropogenic. In addition, the prop-Equiv concentration was determined, where formaldehyde and acetaldehyde were the main producers of tropospheric ozone. The ozone formation potential (OFP) showed that spring and summer are the seasons where carbonyls contribute to the formation of tropospheric ozone.This study represents a first approach of the carbonyl concentration in the city and of the influence of meteorological parameters on the behavior of carbonyls.

Simultaneous observations of peroxyacetyl nitrate and ozone in Central China during static management of COVID-19: Regional transport and thermal decomposition

Peroxyacetyl nitrate (PAN) and ozone (O3) are two typical indicators of photochemical pollution, which are harmful to human body and environment. In this study, PAN and O3 were continuously monitored during static management (SM) of the COVID-19 epidemic in Zhengzhou. Briefly, SM refers to control policies in that all except for essential business are closed; work at home; and no people going out and no gathering, etc. During the SM, the temperature suddenly dropped from 26 °C to 14 °C, which provided a good experimental condition for the study of source transformation, accumulation, and consumption of PAN in the atmosphere. The concentrations of PAN were 0.6, 0.8, and 0.5 ppbv in three periods: before, during, and after the SM. During the SM, the lifetime of PAN was increased due to low temperature, and the accumulation time of PAN was longer, resulting in the increase of PAN concentration in daytime faster than the other two periods. During SM, especially after the temperature drops, the average atmospheric lifetime of PAN was 23.8 h, which was higher than 17.6 h before SM and 13.8 h after SM. This indicated that low temperature was more conducive to the accumulation of PAN. The high potential PAN source (CBPF>0.8) mainly came from the northeast of Zhengzhou, and the wind speed range was between 2.5 and 3 m/s. The backward trajectory analysis showed that 83.3% of the air mass from the northeast and northwest had a greater impact on the PAN concentration in Zhengzhou.

Significant roles of aged dust aerosols on rapid nitrate formation under dry conditions in a semi-arid city

Mineral dust can accelerate secondary aerosol formation under humid conditions. However, it is unclear whether it can promote secondary aerosol formation under dry conditions. To investigate this issue, two years of comprehensive observations was conducted at a semi-arid site, near the dust source regions. Three types of episodes were selected: dust, anthropogenic-dominated, and mixed (mixed with dust and anthropogenic aerosols). Compared to anthropogenic-dominated episodes under humid conditions, rapid nitrate formation was still observed in mixed episodes under dry conditions, suggesting that active metallic oxides in dust, such as titanium dioxide, could promote photochemical reactions of nitrogen dioxide. The detailed evolutionary processes are further illustrated by a typical dust-to-mixed episode. After the arrival of the dust, titanium sharply increased ten-fold and rapid nitrate formation was observed, together with a rapid increase in the two most important photochemical pollutants, ozone and peroxyacetyl nitrate. The increased secondary organic carbon further illustrated that the suspended dust particles accelerated the atmospheric oxidative capacity, thereby enhancing secondary aerosol formation and eventually leading to haze pollution. These results differ from those in humid regions and therefore expand the scientific understanding of the impact of dust aerosols on haze pollution under dry conditions.