Surface ozone (O3) is a crucial air pollutant that affects air quality, human health, agricultural production, and climate change. Studies on long-term O3 variations and their influencing factors are ...essential for understanding O3 pollution and its impact. Here, we conducted an analysis of long-term variations in O3 during 2006–2022 at the Longfengshan Regional Atmosphere Background Station (LFS; 44.44°N, 127.36°E, 330.5 m a.s.l.) situated on the northeastern edge of the Northeast China Plains. The maximum daily 8-h average (MDA8) O3 fluctuated substantially, with the annual MDA8 decreasing significantly during 2006–2015 (−0.62 ppb yr−1, p < 0.05), jumping during 2015–2016 and increasing clearly during 2020–2022. Step multiple linear regression models for MDA8 were obtained using meteorological variables, to decompose anthropogenic and meteorological contributions to O3 variations. Anthropogenic activities acted as the primary drivers of the long-term trends of MDA8 O3, contributing 73% of annual MDA8 O3 variability, whereas meteorology played less important roles (27%). Elevated O3 at LFS were primarily associated with airflows originating from the North China Plain, Northeast China Plain, and coastal areas of North China, primarily occurring during the warm months (May–October). Based on satellite products of NO2 and HCHO columns, the O3 photochemical regimes over LFS revealed NOx-limited throughout the period. NO2 increased first, reaching peak in 2011, followed by substantial decrease; while HCHO exhibited significant increase, contributing to decreasing trend in MDA8 O3 during 2006–2015. The plateauing NO2 and decreasing HCHO may contribute to the increase in MDA8 O3 in 2016. Subsequently, both NO2 and HCHO exhibited notable fluctuations, leading to significant changes in O3. The study results fill the gap in the understanding of long-term O3 trends in high-latitude areas in the Northeast China Plain and offer valuable insights for assessing the impact of O3 on crop yields, forest productivity, and climate change.
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•Surface O3 at LFS fluctuated substantially during 2006–2022.•Anthropogenic impacts dominated the long-term O3 trends and variations.•Changes in meteorology played a less important role in LFS O3.
Tropospheric ozone (O3) and peroxyacetyl nitrate (PAN) are both photochemical pollutants harmful to the ecological environment and human health. In this study, measurements of O3 and PAN as well as ...their precursors were conducted from May to July 2019 at Nam Co station (NMC), a highly pristine high-altitude site in the southern Tibetan Plateau (TP), to investigate how distinct transport processes and photochemistry contributed to their variations. Results revealed that, despite highly similar diurnal variations with steep morning rises and flat daytime plateaus that were caused by boundary layer development and downmixing of free-tropospheric air, day-to-day variations in O3 and PAN were in fact controlled by distinct physicochemical processes. During the dry spring season, air masses rich in O3 were associated with high-altitude westerly air masses that entered the TP from the west or the south, which frequently carried high loadings of stratospheric O3 to NMC. During the summer monsoon season, a northward shift of the subtropical jet stream shifted the stratospheric downward entrainment pathway also to the north, leading to direct stratospheric O3 entrainment into the troposphere of the northern TP, which traveled southwards to NMC within low altitudes via northerly winds in front of ridges or closed high pressures over the TP.
Westerly and southerly air masses, however, revealed low O3 levels due
to the overall less stratospheric O3 within the troposphere of low-latitude regions. PAN, however, was only rich in westerly or southerly air
masses that crossed over polluted regions such as northern India, Nepal or
Bangladesh before entering the TP and arriving at NMC from the south during
both spring and summer. Overall, the O3 level at NMC was mostly
determined by stratosphere–troposphere exchange (STE), which explained
77 % and 88 % of the observed O3 concentration in spring and
summer, respectively. However, only 0.1 % of the springtime day-to-day
O3 variability could be explained by STE processes, while 22 % was
explained during summertime. Positive net photochemical formation was
estimated for both O3 and PAN based on observation-constrained box
modeling. Near-surface photochemical formation was unable to account for
the high O3 level observed at NMC, nor was it the determining
factor for the day-to-day variability of O3. However, it was able to
capture events with elevated PAN concentrations and explain its day-to-day
variations. O3 and PAN formation were both highly sensitive to NOx levels, with PAN being also quite sensitive to volatile organic compound (VOC) concentrations. The rapid development of transportation networks and urbanization within the TP may lead to increased emissions and loadings in NOx and VOCs, resulting in strongly enhanced O3 and PAN formation in downwind pristine regions, which should be given greater attention in future studies.
The light scattering enhancement factor f (RH), defined as the ratio of the light scattering coefficient (σSP) observed under an elevated relative humidity (RH) conditions to that under dry ...conditions, is a crucial parameter for estimating aerosol direct radiative effects and atmospheric visibility. In this paper, a new f (RH) parameterization scheme considering both the influence of aerosol chemical compositions and that of particle number size distribution (PNSD) is proposed based on in situ measurements in the North China Plain. The development of this parameterization scheme includes three steps. First, aerosol hygroscopicity parameter κ is parameterized with aerosol chemical compositions. Then, the ratio between f (RH) fitted parameter κsca (f(RH)=1+κscaRH100−RH) and κ is introduced to correlate f (RH) with κ. The ratio, influenced mostly by PNSD, is described as a function of scattering Ångström exponent (SAE) because the SAE can represent the predominant size of aerosol particles to some extent. Finally, f (RH) cycle is parameterized with κsca. Validation results show that a good consistency between the parameterized and measured f (RH = 80%) is achieved and the correlation coefficient is 0.80. This parameterization scheme between aerosol chemistry and f (RH) can be used in chemical transport models for reducing uncertainties in estimations of direct aerosol radiative forcing and air quality assessments.
•A relationship between the f(RH) fitted parameter (κsca) and the aerosol hygroscopicity parameter (κf(RH)) is found.•The ratio of κsca and κf(RH) increases linearly with the increase of the scattering Ångström exponent.•A new parameterization of f (RH) considering the aerosol chemical compositions is developed.
Laboratory experiments suggest acid-catalyzed aqueous-phase production can promote the formation of isoprene SOA, i.e., 2-methyltetrols. In this study we use ambient observations of the ...2-methyltetrols along with other chemical measurements, as well as meteorological factors to investigate the relative importance of environmental influence for isoprene epoxydiols (IEPOX) SOA formation under atmospheric humidity conditions. The 2-Methyltetrols revealed good relationships with temperature and total solar radiation, but were weakly correlated with aerosol acidity and SO42−. EC-scaled 2-methyltetrols were observed to vary in a narrow pH range (1.5–2.0), indicating aerosol acidity was not a limiting factor for 2-methyltetrols formation. High values of 2-methyltetrols were consistently observed at high total solar radiation, the strong dependence of total solar radiation demonstrated that photochemical processes dominated 2-methyltetrols formation in humid environments. Although 2-methyltetrols can be enhanced by acid-catalyzed aqueous-phase reactions, it is not sufficient to compensate the synchronously weakened photochemical activity influence, leading to an obvious net decrease in the formation of 2-methyltetrols in the ambient. Moreover, aerosol droplet acidity was reduced under high liquid water content (LWC) condition, subsequently diminishing the enhancement of SOA formation by acidity. Overall, our results highlight that the environmental impact factors are highly variable and interplay, influencing the production of 2-methyltetrols, and suggest that the formation pathway of 2-methyltetrols is insensitive to aerosol acidity but dominated by photochemical production process in humid environments.
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•EC scaled 2-methyltetrols show weak relationship with aerosol acidity and SO42−.•2-Methyltetrols formation is insensitive to acidity under humid ambient condition.•2-Methyltetrols formation is strong dependent on temperature in environment.•Environmental factors are integrated influencing the production of 2-methyltetrols.
Tropospheric ozone (O.sub.3) and peroxyacetyl nitrate (PAN) are both photochemical pollutants harmful to the ecological environment and human health. In this study, measurements of O.sub.3 and PAN as ...well as their precursors were conducted from May to July 2019 at Nam Co station (NMC), a highly pristine high-altitude site in the southern Tibetan Plateau (TP), to investigate how distinct transport processes and photochemistry contributed to their variations. Results revealed that, despite highly similar diurnal variations with steep morning rises and flat daytime plateaus that were caused by boundary layer development and downmixing of free-tropospheric air, day-to-day variations in O.sub.3 and PAN were in fact controlled by distinct physicochemical processes. During the dry spring season, air masses rich in O.sub.3 were associated with high-altitude westerly air masses that entered the TP from the west or the south, which frequently carried high loadings of stratospheric O.sub.3 to NMC. During the summer monsoon season, a northward shift of the subtropical jet stream shifted the stratospheric downward entrainment pathway also to the north, leading to direct stratospheric O.sub.3 entrainment into the troposphere of the northern TP, which traveled southwards to NMC within low altitudes via northerly winds in front of ridges or closed high pressures over the TP. Westerly and southerly air masses, however, revealed low O.sub.3 levels due to the overall less stratospheric O.sub.3 within the troposphere of low-latitude regions. PAN, however, was only rich in westerly or southerly air masses that crossed over polluted regions such as northern India, Nepal or Bangladesh before entering the TP and arriving at NMC from the south during both spring and summer. Overall, the O.sub.3 level at NMC was mostly determined by stratosphere-troposphere exchange (STE), which explained 77 % and 88 % of the observed O.sub.3 concentration in spring and summer, respectively. However, only 0.1 % of the springtime day-to-day O.sub.3 variability could be explained by STE processes, while 22 % was explained during summertime. Positive net photochemical formation was estimated for both O.sub.3 and PAN based on observation-constrained box modeling. Near-surface photochemical formation was unable to account for the high O.sub.3 level observed at NMC, nor was it the determining factor for the day-to-day variability of O.sub.3 . However, it was able to capture events with elevated PAN concentrations and explain its day-to-day variations. O.sub.3 and PAN formation were both highly sensitive to NO.sub.x levels, with PAN being also quite sensitive to volatile organic compound (VOC) concentrations. The rapid development of transportation networks and urbanization within the TP may lead to increased emissions and loadings in NO.sub.x and VOCs, resulting in strongly enhanced O.sub.3 and PAN formation in downwind pristine regions, which should be given greater attention in future studies.
The advanced data trading allows data generator's (DG) disturbed data to be traded as both initial and reselling trading modes, which meets DG's raw data privacy and data consumers' (DCs) vast data ...requirement. However, the traded data truthfulness verifiability cannot be guaranteed in the privacy-preserved way. Firstly, due to DG's independent and random disturbance, DC cannot verify whether the traded data is disturbed under his required disturbance parameter without carrying privacy leakage on DG. Secondly, because the reselling trading is allowed, DC can hardly verify the traded data's origin truthfulness under the deceiving of data reseller (DR) while protecting his purchase privacy. Aiming at the above problems, we propose the privacy-preserved data disturbance and truthfulness verification for data trading. Specifically, an honest-but-curious trading server (TS) is introduced to assist our devised private-verifiable imprint-embedded disturbance method where imprint is blinding. Subsequently, TS implements the adaptive truthfulness verification by constructing imprint-embedded individual verification formula and requiring verified participants to decrypt the formula result. The verified participants cannot inform the blinding imprint value to forge the correct result, ensuring the accuracy of the devised verification method. Theoretical analysis proves that participants' privacy is preserved and the traded data's truthfulness can be guaranteed. Extensive experiments using the real-world dataset demonstrate that without any extra privacy cost, our scheme verifies 100% untruthful traded data compared with the existing solutions' 50%.
The light absorption black carbon (BC) and brown carbon (BrC) are two important sources of uncertainties in radiative forcing estimate. Here we investigated the light absorption enhancement (Eabs) of ...BC due to coated materials at an urban (Beijing) and a rural site (Gucheng) in North China Plain (NCP) in winter 2019 by using a photoacoustic extinctiometer coupled with a thermodenuder. Our results showed that the average (±1σ) Eabs was 1.32 (±0.15) at the rural site, which was slightly higher than that at the urban site (1.24 ± 0.15). The dependence of Eabs on coating materials was found to be relatively limited at both sites. However, Eabs presented considerable increases as a function of relative humidity below 70%. Further analysis showed that Eabs during non-heating period in Beijing was mainly caused by secondary components, while it was dominantly contributed by enhanced primary emissions in heating season at both sites. In particular, aerosol particles mixed with coal combustion emissions had a large impact on Eabs (>1.40), while the fresh traffic emissions and freshly oxidized secondary OA (SOA) had limited Eabs (1.00–1.23). Although highly aged or aqueous-phase processed SOA coated on BC showed the largest Eabs, their contributions to the bulk absorption enhancement were generally small. We also quantified the absorption of BrC and source contributions. The results showed the BrC absorption at the rural site was nearly twice that of urban site, yet absorption Ångström exponents were similar. Multiple linear regression analysis highlighted the major sources of BrC being coal combustion emissions and photochemical SOA at both sites with additional biomass burning at the rural site. Overall, our results demonstrated the relatively limited winter light absorption enhancement of BC in different chemical environments in NCP, which needs be considered in regional climate models to improve BC radiative forcing estimates.
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•Eabs has limited dependence on PM coatings in winter at both urban and rural sites in NCP.•Coal combustion emissions and aqueous-phase processing have large impacts on Eabs.•BrC was dominantly from coal combustion, photochemical SOA, and biomass burning.
An observational field campaign was carried out from 20 June to July 31, 2016 at Raoyang, a rural site in the North China Plain (NCP). In-situ measurements of O3 and related gases were obtained and ...analyzed in this work. Heavy photochemical pollution episodes lasting for a few days were observed in the campaign. The episodes could be divided into two categories, with one being influenced by plume from northeast (NE) via Beijing-Tianjin cities and the other from southeast (SE) via Shandong province. The SE episodes were more frequent with higher O3 concentrations and lagged daily peaks of O3 despite of lower concentrations of precursors. Such episodes could last for several days or even a week. In contrast, the NE episode was associated with relatively lower O3 levels and earlier daily O3 peaks though the levels of precursors were higher. The WRF-Chem model was used to study the differences between typical SE and NE episodes in regional distributions of O3 concentrations, chemical regimes of O3 formation, ozone production efficiency (OPE), photochemical age of plume, and evolution of O3 concentration within the boundary layer. Our results suggest that the O3 production regimes were different for the Raoyang site, with the NE episode being VOCs-sensitive and the SE episode in the VOC-sensitive to NOx-sensitive transition regime. In both episodes, a major part of the NCP was under the VOCs-sensitive regime. Plumes in the SE episodes were more aged than those in the NE episode. The OPE values were higher in more aged SE plumes, resulting in higher O3 concentrations despite of lower precursor concentrations. Our results also indicate that downward mixing of O3 in the nocturnal residual layer played an important role in rapid buildup of surface O3 in the next morning in both NE and SE episodes. The formation of photochemical smog seems to be particularly effective in the SE episode since O3 is rapidly produced during daytime, stored aloft at night, and mixed downward to the ground-level, and the process can circulate for several consecutive days. Our study highlights the complicated role of chemical reaction, transport and boundary layer processes in the formation of severe photochemical smog in the region.
•High O3 episodes observed at a rural site in the North China Plain (NCP) in summer 2016.•O3 rapidly produced during daytime and stored aloft at night under southeast winds.•Downward mixing of O3 in the residual layer prompted rapid buildup of surface O3.•O3 formation in the NCP was mainly VOCs-sensitive even after the NOx reduction.
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 (NOy) and their inter-relationship have been studied comparatively less in the winter. Here we measured atmospheric PAN, PPN, O3, NOx, and NOy 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 NOy, with a major constituent of NOx (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 NOx and NOy 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.
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•Low levels of PANs but high NOx and NOy were observed in Beijing during wintertime.•Regional transport acted different roles in shaping the pollutants distribution.•AVOCs dominated the photochemical formation of PANs in winter.•Negative correlation between PAN and O3 resulted from the weak photochemistry.
