Search

The amplification effect of anthropogenic‐biogenic interactions on secondary organic aerosol (SOA) formation remains debated, particularly regarding the impact of anthropogenic emissions on biogenic SOA (BSOA) formation in forests near megacities. This study concurrently measured typical biogenic and anthropogenic SOA tracers during day and night at the summit (1,690 m a.s.l.) and foot (200 m a.s.l.) of the Nanling mountains, a large subtropical forest adjacent to the Pearl River Delta (PRD) in southern China. Results revealed unexpectedly high concentrations of BSOA tracers (149.9 ± 70.5 ng m−3 at the summit and 109.7 ± 51.2 ng m−3 at the foot), surpassing those at most other background sites worldwide. Daytime BSOA tracer levels at the foot were consistent with nighttime levels, whereas the summit showed significantly higher concentrations at night. Nighttime correlations between O₃ and BSOA tracers at the summit suggest that high O₃ levels stimulate BSOA formation. Conversely, a negative correlation between O₃ and isoprene derived SOA (SOAI) tracers at the foot indicates that other oxidants may also influence SOAI formation. BSOA tracer concentrations rose significantly with the arrival of anthropogenic pollutants (e.g., SO₂ and NO₂), indicating that anthropogenic pollution amplifies BSOA formation by enhancing aerosol acidity (pH < 3). This amplification effect could be mitigated by the reduction of aerosol acidity due to increased NH₃ and relative humidity (RH). Our findings provide valuable insights into the interactions between anthropogenic and biogenic emissions on SOA formation and vertical distribution in forests surrounding megacities. Plain Language Summary: Secondary organic aerosol (SOA) makes up a significant portion of global submicron‐sized atmospheric organic aerosols (OA), reaching up to 90% by mass. Understanding its composition and sources is essential for improving air quality and adapting climate change. However, the role of interactions between human‐made (anthropogenic) and natural (biogenic) emissions in enhancing SOA formation is still debated, especially near megacities. To investigate this, we measured biogenic and anthropogenic SOA tracers simultaneously at the summit (1,690 m a.s.l.) and foot (200 m above sea level) of the Nanling mountains, a subtropical forest near the PRD in southern China, during both day and night. Our results showed unexpectedly high concentrations of SOA tracers compared to most global sites. Isoprene‐derived SOA tracers were predominant at the summit, while monoterpene‐derived SOA tracers were more prevalent at the foot. Interactions between anthropogenic and biogenic emissions can enhance biogenic SOA formation in forested areas near megacities, although this effect can be mitigated by increase of ammonia (NH3) and RH. Also, ozone played a crucial role in nighttime biogenic SOA formation at the summit. These findings highlight the impact of anthropogenic‐biogenic interactions on SOA formation and its vertical distribution in urban‐adjacent forests. Key Points: Diurnal patterns of secondary organic aerosol (SOA) tracers were simultaneously investigated at the summit and foot of Mt. NanlingSOA tracer concentrations were found to be significantly higher than those at most other background sites worldwideInteractions between anthropogenic and biogenic emissions amplified SOA formation in forests near megacities, particularly during pollution periods [ABSTRACT FROM AUTHOR]

To mitigate climate change, China is striving to reduce its carbon dioxide (CO 2) emissions before 2030 and has derived a series of national environmental policies to advocate green development. Analysing the changes in regional atmospheric CO 2 concentrations could be more convincing in evaluating the impact of the associated strategies. In this study, a three-year continuous observation campaign of the atmospheric CO 2 mole fraction was first conducted at the summit of the Nanling Mountains, southern China in 2015–2017 to probe the timely feedback of the implementation of the green policies of the government. The effects of regional emissions and removals on the CO 2 mole fraction were subsequently analysed to explore the primary processes and regional contributions driving the background CO 2 concentration. Approximately 86.4% of the observed values were filtered as background events, with average CO 2 concentrations of 395.9 ± 6.8 ppm. The curve-fitting CO 2 mole fraction showed a slight short-term descending trend (0.6–2.2 p.m. y−1) that was rarely seen against the backdrop of a continuous rise of the global average over the years. In addition to the possible impacts of the changes in regional-scale CO 2 sources and sinks, we inferred that the vigorously enforced sustainable development policies of the Chinese government should be accentuated to reduce CO 2 emissions. Although the conclusion relies heavily on a relatively short dataset, this study may globally help the people to reduce carbon emissions. [Display omitted] • Systemic measurement of atmospheric CO 2 concentration in southern China. • Monitored a low background CO 2 concentration below global and China's average. • Reported a rare regional descending event of atmospheric CO 2 concentration. • Verified the feasibility of the 2030 peak CO 2 emission targets for China. • Emphasized the contribution of green development policies to CO 2 reduction. [ABSTRACT FROM AUTHOR]

Toluene is a typical anthropogenic pollutant that has profound impacts on air quality, climate change, and human health, but its sources and sinks over forests surrounding megacities remain unclear. The Nanling Mountains (NM) is a large subtropical forest and is adjacent to the Pearl River Delta (PRD) region, a well-known hotspot for toluene emissions in southern China. However, unexpectedly low toluene concentrations (0.16 ± 0.20 ppbv) were observed at a mountaintop site in NM during a typical photochemical period. A backward trajectory analysis categorized air masses received at the site into three groups, namely, air masses from the PRD, those from central China, and from clean areas. The results revealed more abundant toluene and its key oxidation products, for example, benzaldehyde in air masses mixed with urban plumes from the PRD. Furthermore, a more than three times faster degradation rate of toluene was found in this category of air masses, indicating more photochemical consumption in NM under PRD outflow disturbance. Compared to the categorized clean and central China plumes, the simulated OH peak level in the PRD plumes (15.8 ± 2.2 × 106 molecule cm−3) increased by approximately 30% and 55%, respectively, and was significantly higher than the reported values at other background sites worldwide. The degradation of toluene in the PRD plumes was most likely accelerated by increased atmospheric oxidative capacity, which was supported by isoprene ozonolysis reactions. Our results indicate that receptor forests around megacities are not only highly polluted by urban plumes, but also play key roles in environmental safety by accelerating the degradation rate of anthropogenic pollutants. [Display omitted] • Unexpected low levels of toluene were observed over forests around the Pearl River Delta megacities. • Fastest degradation rate of toluene was first reported at the background site of Nanling Mountains. • Enhancement of atmospheric oxidative capacity over Nanling Mountains accelerated toluene degradation. [ABSTRACT FROM AUTHOR]

Biogenic secondary organic aerosols (BSOA) play a crucial role in atmospheric chemistry, with significant implications for air quality and human health. However, the mechanisms by which anthropogenic emissions influence the formation of BSOA in the real atmosphere have not been fully understood. In this study, fine aerosol (PM 2.5) samples were collected during both the wet and dry seasons at a high-altitude (1690 m) background site in the Nanling Mountains. Eleven typical secondary organic aerosols (SOA) tracers derived from isoprene (SOA I), α/β-pinene (SOA M), β-caryophyllene (SOA S), and toluene (SOA A), as well as water-soluble inorganic ions and the ambient concentrations of isoprene and its two primary oxidation products, were measured. The results showed that the concentrations and composition of SOA tracers exhibited significant seasonal variations. The total concentration of SOA tracers in the wet season (159 ± 100 ng m−3) was almost three times higher than that in the dry season (61 ± 68 ng m−3). SOA I dominated in both seasons, followed by SOA M , SOA S , and SOA A. Compared with other studies, the concentrations of SOA I and SOA A in the wet season were relatively high, which was mainly attributed to the rapid oxidation of their precursors due to the higher atmospheric oxidative capacity. C 5 -alkene triols had a significantly higher proportion in SOA I species than in other mountaintop sites. Temperature was the main factor causing the seasonal difference in the concentration of SOA I. Anthropogenic pollutants significantly promoted the formation of SOA I in the wet season. The influence of anthropogenic pollutants on the reaction pathway of IEPOX was consistent in both seasons, favoring the formation of C 5 -alkene triols. Our study provides vital insights into the molecular characteristics and formation mechanisms of BSOA in a high-altitude background region. It also highlights that the complex air pollution not only affects BSOA concentrations but also the reaction pathways of biogenic volatile organic compounds (BVOCs) transforming into BSOA. • BSOA tracers were firstly measured in Nanling Mountains. • Quick oxidation of locally emitted isoprene was the main contributor to isoprene SOA. • Strong atmospheric oxidation capacity in Mt. Nanling was evidenced by low isoprene and high SOA tracer levels. • In the wet season, anthropogenic pollutants markedly enhanced isoprene SOA formation. • C5-alkene triols were more prevalent in isoprene SOA tracers at our site than at other mountaintops. [ABSTRACT FROM AUTHOR]

• Systemic measured the effectiveness of LDAR surveys addressed fugitive VOCs emissions. • Reported an obvious reduction of the fugitive VOCs leaks after LDAR implementation. • Quantified and characterized the process-based fugitive VOC emissions from a local petroleum refinery. • Emphasized the contribution of the LDAR technology in economic and environmental benefits. Fugitive volatile organic compound (VOC) emissions from the petroleum-refining industry constitute a complex issue in China. This problem has a wide range of implications that require comprehensive measures, including a series of critical policing and legal injunctions in response to regional atmospheric pollution and the resulting safety hazards. In particular, process-based leak detection and repair (LDAR) surveys commonly used in developed countries should be vigorously promoted for fugitive VOC emission reduction. In this study, a campaign was conducted to measure the effectiveness of LDAR surveys by quantifying fugitive VOC emissions caused by equipment leaks in a local petroleum refinery in the Pearl River Delta (PRD) region of China. The leakage points detected in the initial survey accounted for 0.63 % of all the components within the refinery, among which open-ended pipes and valve packing had the highest ratio. After the procedure, the leakage rate was reduced to 0.23 %, suggesting a satisfactory repair performance. The process-based fugitive emission characteristics of each refining unit, storage tank, and loading area were investigated, and the corresponding composite profiles were estimated using the correlation equation method and data from the LDAR survey. Results demonstrated that the total emission of the refinery was 12,595.83 kg/a, with dominant VOC species of alkanes being emitted in nearly all units. Finally, the secondary organic aerosol formation potential (SOAP) and ozone formation potential (OFP) were estimated. All the above results were process-oriented and demonstrated that establishing a local LDAR system that considers the differences in VOC emissions from various manufacturing facilities should be the key strategy for future VOC emission reduction from the entire petroleum refining industry in China. [ABSTRACT FROM AUTHOR]

Over the past decade, secondary pollution characterized by active photochemistry has sharply increased and become the major contributor to air pollution in China, despite the great reduction of primary emissions. Peroxyacetyl nitrate (PAN) is an excellent indicator of photochemical pollution. Observation of PAN in high-elevation atmosphere offers a rare opportunity to understand the degree of photochemical activity in a wide region. In this study, we conducted a field campaign at a high-altitude (1690 m a.s.l.) national background site on the border of South and Central China during photochemically polluted seasons (Sep–Nov 2018). PAN showed significantly higher concentrations than other high-elevation sites worldwide, with hourly mean and maximum values of 0.52 ± 0.45 ppbv and 2.33 ppbv, respectively. Episodes with much higher PAN levels (1.03 ± 0.40 ppbv) than backgrounds (0.24 ± 0.13 ppbv) were captured. Nighttime peaks suggested mixed impacts of regional transport and VOCs oxidation by nitrate radical and O 3. High background O 3 (44.30 ± 0.44 ppbv) was derived from the significant positive correlation of O 3 with PAN. Contributions of downward transported PAN from upper troposphere were found to be non-negligible. Further analyses revealed that regional transport from Central China contributed substantially to the high levels of PAN, with only a minor contribution coming from the south where the Pearl River Delta (PRD) metropolitan region is located. Our results might indicate the great achievement in air quality improvement in the PRD, and also suggest that a strategic shift of control focus from metropolitan to developing areas is urgently needed for mitigating the severe photochemical pollution in China. [Display omitted] • First observations of PAN in the high-elevation background atmosphere of South-Central China. • Higher PAN concentrations than those at other high-elevation sites worldwide were observed. • Relatively high background O 3 was obtained from linear regression of O 3 and PAN. • Air masses coming from Central China significantly enhance the PAN levels. • Strategic shift of control focus from metropolitan to developing areas in China is suggested. [ABSTRACT FROM AUTHOR]

Five-year continuous O 3 measurements were conducted for the first time at the summit of Nanling Mountains (112.88° E, 24.68° N, 1690 m a.s.l), southern China in 2013–2017. Unlike most mountains over the world with O 3 maximum in spring or summer, Nanling showed O 3 maximum in mid-autumn (October; 62.8 ± 0.7 ppbv, ± 95% confidence intervals) and minimum in summer (July; 46.6 ± 0.7 ppbv). This distinct seasonal cycle of O 3 at Nanling was mainly caused by the special impact of Asian monsoon in southern China, which brought clean maritime background air and fresh emissions of the Pearl River Delta (PRD) region in spring/summer, and polluted northern continental air masses in autumn/winter, respectively. Further comparisons found that O 3 of Nanling in four seasons were all higher than other similar mountainous background sites, making the annual mean of O 3 (55.0 ± 0.2 ppbv) at Nanling the second highest that ever reported in the mountainous sites worldwide. Moreover, the diurnal variation showed the higher impact of regional transport during nighttime from the free troposphere (FT) and presented the potential air exchange between the FT and local atmosphere in the plenary boundary layer on the summit of Nanling. Both the seasonal variation and high O 3 level indicated a strong impact of anthropogenic emissions from alternatively PRD/northern China on O 3 pollution in this mountainous background region. This study diversifies the seasonal variations among mountains over the world, and also illustrates the complicated impact of anthropogenic emissions on the mountainous atmosphere in southern China. • The annual mean of O 3 (55 ± 18 ppbv) at Nanling was the second highest in the mountainous sites worldwide. • Different from others, Nanling showed O 3 maximum in mid-autumn and minimum in summer due to Asian monsoon. • Diurnal variations of O 3 at Nanling showed a minimum in the morning and a maximum at early night. [ABSTRACT FROM AUTHOR]

Glyoxal (Gly) and methylglyoxal (Mgly) are the intermediate products of several volatile organic compounds (VOCs) as well as the precursors of brown carbon and may play key roles in photochemical pollution and regional climate change in the Tibetan Plateau (TP). However, their sources and atmospheric behaviors in the TP remain unclear. During the second Tibetan Plateau Scientific Expedition and Research in the summer of 2020, the concentrations of Gly (0.40 ± 0.30 ppbv) and Mgly (0.57 ± 0.16 ppbv) observed in Lhasa, the most densely populated city in the TP, had increased by 20 and 15 times, respectively, compared to those measured a decade previously. Owing to the strong solar radiation, secondary formations are the dominant sources of both Gly (71%) and Mgly (62%) in Lhasa. In addition, primary anthropogenic sources also play important roles by emitting Gly and Mgly directly and providing abundant precursors (e.g., aromatics). During ozone pollution episodes, local anthropogenic sources (industries, vehicles, solvent usage, and combustion activities) contributed up to 41% and 45% in Gly and Mgly levels, respectively. During non-episode periods, anthropogenic emissions originating from the south of Himalayas also have non-negligible contributions. Our results suggest that in the previous decade, anthropogenic emissions have elevated the levels of Gly and Mgly in the TP dramatically. This study has important implications for understanding the impact of human activities on air quality and climate change in this ecologically fragile area., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Imidazoles are important constituents in atmospheric brown carbon and have gained increasing attention in the past decade. Although imidazoles have been studied widely in laboratories, the sparse field observations severely limit the understanding of imidazole's abundance and sources in the atmosphere. In this study, we measured particle-bound imidazoles and their precursors at a background forest site in the Nanling Mountains of southern China. The average concentration of imidazoles (4.17 ± 3.76 ng/m 3 ) was found to be significantly higher than other background sites worldwide. Further analyses revealed that a majority of imidazoles (59.1%) at the site originated from secondary formation through reactions of dicarbonyls (e.g., glyoxal and methylglyoxal) and reduced nitrogen species, with relatively minor contributions from regional transport (32.8%) and biomass burning (8.1%). In addition, the key factors influencing secondary formation of imidazoles, such as relative humidity, water-soluble inorganic ions, and pH, were analyzed. Our results indicated that the secondary formation of imidazoles can be greatly enhanced under high humidity conditions, particularly during fog events. Overall, this study offers valuable insights into potential sources and influencing factors of ambient imidazoles in background atmospheres., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)