Global variability in atmospheric new particle formation mechanisms.

A key challenge in aerosol pollution studies and climate change assessment is to understand how atmospheric aerosol particles are initially formed1,2. Although new particle formation (NPF) mechanisms have been described at specific sites3-6, in most regions, such mechanisms remain uncertain to a large extent because of the limited ability of atmospheric models to simulate critical NPF processes1,7. Here we synthesize molecular-level experiments to develop comprehensive representations of 11 NPF mechanisms and the complex chemical transformation of precursor gases in a fully coupled global climate model. Combined simulations and observations show that the dominant NPF mechanisms are distinct worldwide and vary with region and altitude. Previously neglected or underrepresented mechanisms involving organics, amines, iodine oxoacids and HNO3 probably dominate NPF in most regions with high concentrations of aerosols or large aerosol radiative forcing; such regions include oceanic and human-polluted continental boundary layers, as well as the upper troposphere over rainforests and Asian monsoon regions. These underrepresented mechanisms also play notable roles in other areas, such as the upper troposphere of the Pacific and Atlantic oceans. Accordingly, NPF accounts for different fractions (10-80%) of the nuclei on which cloud forms at 0.5% supersaturation over various regions in the lower troposphere. The comprehensive simulation of global NPF mechanisms can help improve estimation and source attribution of the climate effects of aerosols.

Coping with the concurrent heatwaves and ozone extremes in China under a warming climate.

Intensive human activity has brought about unprecedented climate and environmental crises, in which concurrent heatwaves and ozone extremes pose the most serious threats. However, a limited understanding of the comprehensive mechanism hinders our ability to mitigate such compound events, especially in densely populated regions like China. Here, based on field observations and climate-chemistry coupled modelling, we elucidate the linkage between human activities and the climate system in heat-related ozone pollution. In China, we have observed that both the frequency and intensity of heatwaves have almost tripled since the beginning of this century. Moreover, these heatwaves are becoming more common in urban clusters with serious ozone pollution. Persistent heatwaves during the extremely hot and dry summers of 2013 and 2022 accelerated photochemical ozone production by boosting anthropogenic and biogenic emissions, and aggravated ozone accumulation by suppressing dry deposition due to water-stressed vegetation, leading to a more than 30% increase in ozone pollution in China's urban areas. The sensitivity of ozone to heat is demonstrated to be substantially modulated by anthropogenic emissions, and China's clean air policy may have altered the relationship between ozone and temperature. Climate model projections further highlight that the high-emission climate-socioeconomic scenario tends to intensify the concurrent heat and ozone extremes in the next century. Our results underscore that the implementation of a strict emission strategy will significantly reduce the co-occurrence of heatwaves and ozone extremes, achieving climate and environmental co-benefits.

Air quality improvements can strengthen China's food security.

Air pollution exerts crucial influence on crop yields and impacts regional and global food supplies. Here we employ a statistical model using satellite-based observations and flexible functional forms to analyse the synergistic effects of reductions in ozone and aerosols on China's food security. The model consistently shows that ozone is detrimental to crops, whereas aerosol has variable effects. China's maize, rice and wheat yields are projected to increase by 7.84%, 4.10% and 3.43%, respectively, upon reaching two air quality targets (60 µg m-3 for peak-season ozone and 35 µg m-3 for annual fine particulate matter). Average calories produced from these crops would surge by 4.51%, potentially allowing China to attain grain self-sufficiency 2 years earlier than previously estimated. These results show that ozone pollution control should be a high priority to increase staple crop edible calories, and future stringent air pollution regulations would enhance China's food security.

Investigation on the budget of peroxyacetyl nitrate (PAN) in the Yangtze River Delta: Unravelling local photochemistry and regional impact.

Peroxyacetyl nitrate (PAN) is a significant indicator of atmospheric photochemical pollution, which can influence the regional distribution of ozone (O3) and hydroxyl radical (OH) through long-range transport. However, investigations of PAN incorporating comprehensive measurement and explicit modeling analysis are limited, hindering complete understandings of its temporal behavior, sources, and impacts on photochemistry. Here we conducted a 1-year continuous observation of PAN and relative atmospheric species in Nanjing located in Yangtze River Delta (YRD). The annual mean concentration of PAN was 0.62 ± 0.49 ppbv and showed a bimodal monthly variation, peaking in April-June and November-January, respectively. This pattern is different from the typical pattern of photochemistry, suggesting important contributions of other non-photochemical processes. We further analyzed the PAN budget using an observation-based model, by which, PAN from local photochemical production and regional source could be decoupled. Our results revealed that local photochemical production of PAN is the sole contributor to PAN in summer, whereas about half of the total PAN concentration is attributed to regional source in winter. Although the formation of PAN can suppress the atmospheric oxidation capacity by consuming the peroxyacetyl radical and nitrogen dioxide (NO2), our analyses suggested this effect is minor at our station (-3.2 ± 1.1 % in summer and - 7.2 ± 2.8 % in winter for O3 formation). However, it has the potential to enhance O3 and OH formation by 14.16 % and 5.93 %, if transported to cleaner environments with air pollutants halved. Overall, our study highlights the importance of both local photochemistry and regional process in PAN budget and provides a useful evaluation on the impact of PAN on atmospheric oxidation capacity.

Modeling the Formation of Organic Compounds across Full Volatility Ranges and Their Contribution to Nanoparticle Growth in a Polluted Atmosphere.

Nanoparticle growth influences atmospheric particles' climatic effects, and it is largely driven by low-volatility organic vapors. However, the magnitude and mechanism of organics' contribution to nanoparticle growth in polluted environments remain unclear because current observations and models cannot capture organics across full volatility ranges or track their formation chemistry. Here, we develop a mechanistic model that characterizes the full volatility spectrum of organic vapors and their contributions to nanoparticle growth by coupling advanced organic oxidation modeling and kinetic gas-particle partitioning. The model is applied to Nanjing, a typical polluted city, and it effectively captures the volatility distribution of low-volatility organics (with saturation vapor concentrations <0.3 µg/m3), thus accurately reproducing growth rates (GRs), with a 4.91% normalized mean bias. Simulations indicate that as particles grow from 4 to 40 nm, the relative fractions of GRs attributable to organics increase from 59 to 86%, with the remaining contribution from H2SO4 and its clusters. Aromatics contribute much to condensable organic vapors (∼37%), especially low-volatility vapors (∼61%), thus contributing the most to GRs (32-46%) as 4-40 nm particles grow. Alkanes also contribute 19-35% of GRs, while biogenic volatile organic compounds contribute minimally (<13%). Our model helps assess the climatic impacts of particles and predict future changes.

An overlooked oxidation mechanism of toluene: computational predictions and experimental validations.

Secondary organic aerosols (SOAs) influence the Earth's climate and threaten human health. Aromatic hydrocarbons (AHs) are major precursors for SOA formation in the urban atmosphere. However, the revealed oxidation mechanism dramatically underestimates the contribution of AHs to SOA formation, strongly suggesting the importance of seeking additional oxidation pathways for SOA formation. Using toluene, the most abundant AHs, as a model system and the combination of quantum chemical method and field observations based on advanced mass spectrometry, we herein demonstrate that the second-generation oxidation of AHs can form novel epoxides (TEPOX) with high yield. Such TEPOX can further react with H2SO4 or HNO3 in the aerosol phase to form less-volatile compounds including novel non-aromatic and ring-retaining organosulfates or organonitrates through reactive uptakes, providing new candidates of AH-derived organosulfates or organonitrates for future ambient observation. With the newly revealed mechanism, the chemistry-aerosol box modeling revealed that the SOA yield of toluene oxidation can reach up to 0.35, much higher than 0.088 based on the original mechanism under the conditions of pH = 2 and 0.1 ppbv NO. This study opens a route for the formation of reactive uptake SOA precursors from AHs and significantly fills the current knowledge gap for SOA formation in the urban atmosphere.

Recent Progress in Atmospheric Chemistry Research in China: Establishing a Theoretical Framework for the "Air Pollution Complex".

Atmospheric chemistry research has been growing rapidly in China in the last 25 years since the concept of the "air pollution complex" was first proposed by Professor Xiaoyan TANG in 1997. For papers published in 2021 on air pollution (only papers included in the Web of Science Core Collection database were considered), more than 24 000 papers were authored or co-authored by scientists working in China. In this paper, we review a limited number of representative and significant studies on atmospheric chemistry in China in the last few years, including studies on (1) sources and emission inventories, (2) atmospheric chemical processes, (3) interactions of air pollution with meteorology, weather and climate, (4) interactions between the biosphere and atmosphere, and (5) data assimilation. The intention was not to provide a complete review of all progress made in the last few years, but rather to serve as a starting point for learning more about atmospheric chemistry research in China. The advances reviewed in this paper have enabled a theoretical framework for the air pollution complex to be established, provided robust scientific support to highly successful air pollution control policies in China, and created great opportunities in education, training, and career development for many graduate students and young scientists. This paper further highlights that developing and low-income countries that are heavily affected by air pollution can benefit from these research advances, whilst at the same time acknowledging that many challenges and opportunities still remain in atmospheric chemistry research in China, to hopefully be addressed over the next few decades.

Unified theoretical framework for black carbon mixing state allows greater accuracy of climate effect estimation.

Black carbon (BC) plays an important role in the climate system because of its strong warming effect, yet the magnitude of this effect is highly uncertain owing to the complex mixing state of aerosols. Here we build a unified theoretical framework to describe BC's mixing states, linking dynamic processes to BC coating thickness distribution, and show its self-similarity for sites in diverse environments. The size distribution of BC-containing particles is found to follow a universal law and is independent of BC core size. A new mixing state module is established based on this finding and successfully applied in global and regional models, which increases the accuracy of aerosol climate effect estimations. Our theoretical framework links observations with model simulations in both mixing state description and light absorption quantification.

Atmospheric Reactive Nitrogen Deposition from 2010 to 2021 in Lake Taihu and the Effects on Phytoplankton.

The effects of nitrogen deposition reduction on nutrient loading in freshwaters have been widely studied, especially in remote regions. However, understanding of the ecological effects is still rather limited. Herein, we re-estimated nitrogen deposition, both of wet and dry deposition, in Lake Taihu with monthly monitoring data from 2010 to 2021. Our results showed that the atmospheric deposition of reactive nitrogen (namely NH4+ and NO3-) in Lake Taihu was 4.94-11.49 kton/yr, which equaled 13.9%-27.3% of the riverine loading. Dry deposition of NH4+ and NO3- contributed 53.1% of the bulk deposition in Lake Taihu. Ammonium was the main component of both wet and dry deposition, which may have been due to the strong agriculture-related activities around Lake Taihu. Nitrogen deposition explained 24.9% of the variation in phytoplankton community succession from 2010 to 2021 and was the highest among all the environmental factors. Atmospheric deposition offset the effects of external nitrogen reduction during the early years and delayed the emergence of nitrogen-fixing cyanobacterial dominance in Lake Taihu. Our results implied that a decrease in nitrogen deposition due to a reduction in fertilizer use, especially a decrease in NH4+ deposition, could limit diatoms and promote non-nitrogen-fixing cyanobacterial dominance, followed by nitrogen-fixing taxa. This result was also applied to other shallow eutrophic lakes around the middle and lower reaches of the Yangtze River, where significant reduction of fertilizer use recorded during the last decades.

Salmonella enterica serovar Paratyphi A-induced immune response in Caenorhabditis elegans depends on MAPK pathways and DAF-16.

Salmonella enterica serovar Paratyphi A (S. Paratyphi A) is a pathogen that can cause enteric fever. According to the recent epidemic trends of typhoid fever, S. Paratyphi A has been the major important causative factor in paratyphoid fever. An effective vaccine for S. Paratyphi A has not been developed, which made it a tricky public health concern. Until now, how S. Paratyphi A interacts with organisms remain unknown. Here using lifespan assay, we found that S. Paratyphi A could infect Caenorhabditis elegans (C. elegans) at 25°C, and attenuate thermotolerance. The immune response of C. elegans was mediated by tir-1, nsy-1, sek-1, pmk-1, mpk-1, skn-1, daf-2 and daf-16, suggesting that S. Paratyphi A could regulate the MAPK and insulin pathways. Furthermore, we observed several phenotypical changes when C. elegans were fed S. Paratyphi A, including an accelerated decline in body movement, reduced the reproductive capacity, shortened spawning cycle, strong preference for OP50, arrested pharyngeal pumping and colonization of the intestinal lumen. The virulence of S. Paratyphi A requires living bacteria and is not mediated by secreting toxin. Using hydrogen peroxide analysis and quantitative RT-PCR, we discovered that S. Paratyphi A could increase oxidative stress and regulate the immune response in C. elegans. Our results sheds light on the infection mechanisms of S. Paratyphi A and lays a foundation for drugs and vaccine development.

Response of organic aerosol characteristics to emission reduction in Yangtze River Delta region.

Organic aerosol (OA) is a major component of atmospheric particulate matter (PM) with complex composition and formation processes influenced by various factors. Emission reduction can alter both precursors and oxidants which further affects secondary OA formation. Here we provide an observational analysis of secondary OA (SOA) variation properties in Yangtze River Delta (YRD) of eastern China in response to large scale of emission reduction during Chinese New Year (CNY) holidays from 2015 to 2020, and the COVID-19 pandemic period from January to March, 2020. We found a 17% increase of SOA proportion during the COVID lockdown. The relative enrichment of SOA is also found during multi-year CNY holidays with dramatic reduction of anthropogenic emissions. Two types of oxygenated OA (OOA) influenced by mixed emissions and SOA formation were found to be the dominant components during the lockdown in YRD region. Our results highlight that these emission-reduction-induced changes in organic aerosol need to be considered in the future to optimize air pollution control measures. Electronic Supplementary Material: Supplementary material is available in the online version of this article at 10.1007/s11783-023-1714-0 and is accessible for authorized users.

Ionic Strength Enhances the Multiphase Oxidation Rate of Sulfur Dioxide by Ozone in Aqueous Aerosols: Implications for Sulfate Production in the Marine Atmosphere.

Multiphase oxidation of sulfur dioxide (SO2) by ozone (O3) in alkaline sea salt aerosols is an important source of sulfate aerosols in the marine atmosphere. However, a recently reported low pH of fresh supermicron sea spray aerosols (mainly sea salt) would argue against the importance of this mechanism. Here, we investigated the impact of ionic strength on the kinetics of multiphase oxidation of SO2 by O3 in proxies of aqueous acidified sea salt aerosols with buffered pH of ∼4.0 via well-controlled flow tube experiments. We find that the sulfate formation rate for the O3 oxidation pathway proceeds 7.9 to 233 times faster under high ionic strength conditions of 2-14 mol kg-1 compared to the dilute bulk solutions. The ionic strength effect is likely to sustain the importance of multiphase oxidation of SO2 by O3 in sea salt aerosols in the marine atmosphere. Our results indicate that atmospheric models should consider the ionic strength effects on the multiphase oxidation of SO2 by O3 in sea salt aerosols to improve the predictions of the sulfate formation rate and the sulfate aerosol budget in the marine atmosphere.

Rapid decline of carbon monoxide emissions in the Fenwei Plain in China during the three-year Action Plan on defending the blue sky.

The Fenwei Plain is one of China's most polluted regions, with poor atmospheric dispersion conditions and an outdated energy structure. After implementing multiple policies in recent years, significant reductions in air pollutant concentrations were observed. In this study, based on the Lagrangian-Bayesian inversion framework FLEXINVERT, we constructed a variable resolution inversion system focusing on the Fenwei Plain and inferred the carbon monoxide (CO) emissions using in-situ atmospheric CO observations from April 2014 to March 2020. We analyzed the spatiotemporal variations of the CO emissions and discussed their causes, especially the effect of the "Three-year Action Plan on Defending the Blue Sky" (TAPDBS). Before the policy, CO emissions temporarily increased, and the overall decrease in CO emissions per unit of Gross Domestic Product (GDP) slowed down. When the policy was implemented, CO emission fluxes declined sharply, with an average drop of 28%, accompanied by an even higher 37% decrease of CO emission per GDP. The reasons for the decline in CO emissions in Shanxi, Shaanxi and Henan are diverse. The decrease in energy intensity is the reason for CO emission reduction in Shannxi and Henan province but not in Shanxi province. This research fills the gap in emission information in recent years and confirms that TAPDBS has brought a breakthrough in both economic development and air quality protection in the Fenwei Plain.

Smoke-weather interaction affects extreme wildfires in diverse coastal regions.

Extreme wildfires threaten human lives, air quality, and ecosystems. Meteorology plays a vital role in wildfire behaviors, and the links between wildfires and climate have been widely studied. However, it is not fully clear how fire-weather feedback affects short-term wildfire variability, which undermines our ability to mitigate fire disasters. Here, we show the primacy of synoptic-scale feedback in driving extreme fires in Mediterranean and monsoon climate regimes in the West Coast of the United States and Southeastern Asia. We found that radiative effects of smoke aerosols can modify near-surface wind, air dryness, and rainfall and thus worsen air pollution by enhancing fire emissions and weakening dispersion. The intricate interactions among wildfires, smoke, and weather form a positive feedback loop that substantially increases air pollution exposure.

Radial growth of Korshinsk peashrub and its response to drought in different sub-arid climate regions of northwest China.

The increased frequency and intensity of droughts have seriously affected the stability of plantation ecosystems in the Chinese Loess Plateau. Caragana korshinskii Kom. was the dominant afforested shrub species in this region. Evaluating the radial growth of C. korshinskii and its response to drought can provide valuable information for sustainable management of plantations in the context of climate change. In this study, based on 237 shrub C. korshinskii annual ring samples from nine sites in different climate regions, we investigated the response of C. korshinskii radial growth to climate (temperature, precipitation, and monthly resolved standardized precipitation evapotranspiration index (SPEI_01)), and evaluated the differences between them using calculated indices of drought resistance, recovery, and resilience. The results demonstrate that the radial growth of C. korshinskii was mainly limited by drought stress in the previous September in arid regions and in March and June in semi-arid regions, whereas C. korshinskii in semi-humid regions was less influenced by drought stress. Recovery after drought decreased with increasing resistance, and resilience increased significantly with increasing resistance and recovery. Differences in precipitation were found to be the main factor generating variations in shrub resilience; with an increase in precipitation, the recovery and resilience after drought gradually increased. For plantation management, this study suggests that efficient utilization of precipitation resources and site-specific afforestation in different climate and site conditions may help to enhance resilience and improve the ecological service function of plantation forests in the Loess Plateau.

Dust emission reduction enhanced gas-to-particle conversion of ammonia in the North China Plain.

Ammonium salt is an important component of particulate matter with aerodynamic diameter less than 2.5 µm (PM2.5) and has significant impacts on air quality, climate, and natural ecosystems. However, a fundamental understanding of the conversion kinetics from ammonia to ammonium in unique environments of high aerosol loading is lacking. Here, we report the uptake coefficient of ammonia (γNH3) on ambient PM2.5 varying from 2.2 × 10-4 to 6.0 × 10-4 in the North China Plain. It is significantly lower than those on the model particles under simple conditions reported in the literature. The probability-weighted γNH3 increases obviously, which is well explained by the annual decrease in aerosol pH due to the significant decline in alkali and alkali earth metal contents from the emission source of dust. Our results elaborate on the complex interactions between primary emissions and the secondary formation of aerosols and the important role of dust in atmospheric chemistry.

Weakened Haze Mitigation Induced by Enhanced Aging of Black Carbon in China.

A great challenge for haze pollution mitigation with the existing emission control measures in China is ozone (O3) increase. The chemical processes leading to weakened haze mitigation are still poorly understood. Our work identifies the enhanced aging chemistries of black carbon (BC) with increasing O3 as an essential driver to weaken haze mitigation based on field observations during autumn/winter haze periods in 2014 and 2018 in North China Plain. The enhanced atmospheric oxidation capacity induced by increasing O3 promotes the initial aging of accumulated fresh BC from continuous emission under haze pollution conditions and consequently improves the hygroscopicity of BC-containing particles to provide more particulate surfaces and volumes for aqueous and heterogeneous chemistries. The enhanced BC aging amplifies PM2.5 concentrations by ∼20%, which can be broken by concurrent reductions in multipollutant emissions (i.e., BC, nitrogen oxides, and volatile organic compounds), especially from residential and industrial sources. Moreover, enhanced BC aging implies an adverse effect of O3 increase on climate change. Observationally enhanced BC aging will help to constrain estimations of the interactions among O3 increase, haze pollution, and climate warming in recent years in China.

The Characteristics of Radial Growth and Ecological Response of Caragana korshinskii Kom. Under Different Precipitation Gradient in the Western Loess Plateau, China.

Understanding the temporal-spatial variability of tree radial growth and ecological response is the basis for assessing forest vulnerability in sight of climate change. We studied stands of the shrub Caragana korshinskii Kom. at four sampling sites (natural forest CL and plantation forests XZJ, CK and TPX) that spanned the different precipitation gradient (180-415 mm) across China's western Loess Plateau, and demonstrated its radial growth dynamics and ecological response. We found that the growth of natural C. korshinskii in arid regions have adapted and cope with regional environmental changes and radial growth was less affected by drought stress. However, the growth of planted C. korshinskii was significantly affected by drought stress in arid and semi-arid regions, especially during the growing season (from June to September). Variations in radial growth rates and growth indicators such as shrub height, canopy area are consistent with the climate-growth relationship. With increase of precipitation, the limiting of drought on the growth of planted C. korshinskii gradually decreased and the amount of radial growth variation explained by drought decreased from 53.8 to 34.2% and 22.3% from 270 to 399 and 415 mm of precipitation, respectively. The age-related radial growth trend shows that radial growth increased until 4 years of age, then decreased rapidly until 12-14 years of age, and then eventually tend to stabilized. In the context of climate warming and humidification, increased precipitation and regular branch coppicing management at around 12 years old will help to mitigate the limitation of drought on the growth of C. korshinskii. Moreover, the initial planting density should be tailored to local precipitation conditions (below 5,000 shrubs per hectare). The above results have important practical significance for the maintenance of the stability and sustainable management of plantation forests in the western Loess Plateau.

The striking effect of vertical mixing in the planetary boundary layer on new particle formation in the Yangtze River Delta.

New particle formation (NPF) induces a sharp increase in ultrafine particle number concentrations and potentially acts as an important source of cloud condensation nuclei (CCN). As the densely populated area of China, the Yangtze River Delta (YRD) region shows a high frequency of observed NPF events at the ground level, especially in spring. Although recent observational studies suggested a possible connection between NPF at the higher altitudes and ground level, the role played by vertical mixing, particularly in the planetary boundary layer (PBL) is not fully understood. Here we integrate measurements in Nanjing on 15-20 April 2018, and the NPF-explicit Weather Research and Forecast coupled with chemistry (WRF-Chem) model simulations to better understand the governing mechanisms of the NPF and CCN. Our results indicate that newly formed particles at the boundary layer top could be transported downward by vertical mixing as the PBL develops. A numerical sensitivity simulation created by eliminating aerosol vertical mixing suppresses both the downward transport of particles formed at a higher altitude and the dilution of particles at the ground level. The resulting higher Fuchs surface area at the ground level, together with the lack of downward transport, yields a sharp weakening of NPF strength and delayed start of NPF therein. The aerosol vertical mixing, therefore, leads to a more than double increase of surface CN10-40 and a one third decrease of boundary layer top CN10-40. Additionally, the continuous growth of nucleated ultrafine particles at the boundary layer top is strongly steered by the upward transport of condensable gases, with close to half increase of particle number concentrations in Aitken mode and CCN at a supersaturation rate of 0.75%. The findings may bridge the gap in understanding the complex interaction between PBL dynamics and NPF events, reducing the uncertainty in assessing the climate impact of aerosols.

Air quality and health co-benefits of China's carbon dioxide emissions peaking before 2030.

Recent evidence shows that carbon emissions in China are likely to peak ahead of 2030. However, the social and economic impacts of such an early carbon peak have rarely been assessed. Here we focus on the economic costs and health benefits of different carbon mitigation pathways, considering both possible socio-economic futures and varying ambitions of climate policies. We find that an early peak before 2030 in line with the 1.5 °C target could avoid ~118,000 and ~614,000 PM2.5 attributable deaths under the Shared Socioeconomic Pathway 1, in 2030 and 2050, respectively. Under the 2 °C target, carbon mitigation costs could be more than offset by health co-benefits in 2050, bringing a net benefit of $393-$3,017 billion (in 2017 USD value). This study not only provides insight into potential health benefits of an early peak in China, but also suggests that similar benefits may result from more ambitious climate targets in other countries.