Current atmospheric quality models usually underestimate the level of ambient secondary organic aerosol(SOA), one of the possible reasons is that the precursors at different concentrations may undergo different oxidat...Current atmospheric quality models usually underestimate the level of ambient secondary organic aerosol(SOA), one of the possible reasons is that the precursors at different concentrations may undergo different oxidation processes and further affect SOA formation. Therefore, there is a need to perform more chamber studies to disclose the influence. In this work, SOA formation over a wide range of initial precursor concentrations(tens of ppb to hundreds of ppb levels) was investigated in a 30 m3 indoor smog chamber,and mainly through the analysis of multiple generations of VOCs detected from HR-To FPTRMS to expound the difference in the oxidation process between low and high precursor concentrations. Compared to high initial concentrations, gas-phase intermediates formed at low concentrations had a higher intensity by about one order of magnitude, and the lowvolatility compounds also had a higher formation potential due to the competition between semi-volatile intermediates and precursors with oxidants. In addition, the formed SOA was more oxidized with higher f44 value(0.14 ± 0.02) and more relevant to real atmosphere than that formed at high concentrations. This work should help to deeply understand SOA formation and improve the performance of air quality models for SOA simulation.展开更多
In order to evaluate the secondary aerosol formation potential at a suburban site of Beijing,in situ perturbation experiments in a potential aerosol mass（PAM） reactor were carried out in the winter of 2014.The varia...In order to evaluate the secondary aerosol formation potential at a suburban site of Beijing,in situ perturbation experiments in a potential aerosol mass（PAM） reactor were carried out in the winter of 2014.The variations of secondary aerosol formation as a function of time,OH exposure,and the concentrations of gas phase pollutants and particles were reported in this study.Two periods with distinct secondary aerosol formation potentials,marked as Period Ⅰ and Period Ⅱ,were identified during the observation.In Period Ⅰ,the secondary aerosol formation potential was high,and correlated well to the air pollutants,i.e.,SO2,NO2,and CO.The maximal secondary aerosol formation was observed with an aging time equivalent to about 3 days of atmospheric oxidation.In period Ⅱ,the secondary aerosol formation potential was low,with no obvious correlation with the air pollutants.Meanwhile,the aerosol mass decreased,instead of showing a peak,with increasing aging time.Backward trajectory analysis during the two periods confirmed that the air mass in Period Ⅰwas mainly from local sources,while it was attributed mostly to long distance transport in Period Ⅱ.The air lost its reactivity during the long transport and the particles became highly aged,resulting in a low secondary aerosol formation potential.Our experimental results indicated that the in situ measurement of the secondary aerosol formation potential could provide important information for evaluating the contributions of local emission and long distance transport to the aerosol pollution.展开更多
Air pollution is a major challenge to the improvement of urban environmental quality.The control of air pollution still faces severe challenges,especially in developing countries,such as ozone pollution control.Ozone ...Air pollution is a major challenge to the improvement of urban environmental quality.The control of air pollution still faces severe challenges,especially in developing countries,such as ozone pollution control.Ozone is a typical secondary air pollutant,and its formation chemistry from its precursors(NOx and volatile organic compounds)is highly nonlinear,which caused the emission reduction of its precursors is not always effective and therefore new assisted approaches to control of ozone pollution are needed.Photocatalysis and ambient catalysis technology are expected to be applied in open atmosphere as a new booster to the direct purification of air pollutants in emission sources.In this perspective,we summarize the current knowledge about the photocatalysis and ambient catalysis technology for the removal of air pollutants under natural photothermal conditions.Based on these technologies,we propose the concept of“Environmental Catalytic City”,which refers to the spontaneous purification of low concentration urban air pollutants in the atmosphere by catalytic materials coating on the artificial surfaces,such as building surfaces in the city.In this way,the urban city with self-purification function can remove air pollution without additional energy consumption.The further improvement,development,and application of the“Environmental Catalytic City”is also discussed.展开更多
The strict control measures and social lockdowns initiated to combat COVID-19 epidemic have had a notable impact on air pollutant concentrations.According to observation data obtained from the China National Environme...The strict control measures and social lockdowns initiated to combat COVID-19 epidemic have had a notable impact on air pollutant concentrations.According to observation data obtained from the China National Environmental Monitoring Center,compared to levels in 2019,the average concentration of NO_(2) in early 2020 during COVID-19 epidemic has decreased by 53%,50%,and 30%in Wuhan city,Hubei Province(Wuhan excluded),and China(Hubei excluded),respectively.Simultaneously,PM_(2.5) concentration has decreased by 35%,29%,and 19%in Wuhan,Hubei(Wuhan excluded),and China(Hubei excluded),respectively.Less significant declines have also been found for SO_(2) and CO concentrations.We also analyzed the temporal variation and spatial distribution of air pollutant concentrations in China during COVID-19 epidemic.The decreases in PM_(2.5) and NO_(2) concentrations showed relatively consistent temporal variation and spatial distribution.These results support control of NO x to further reduce PM_(2.5) pollution in China.The concurrent decrease in NOx and PM_(2.5) concentrations resulted in an increase of O3 concentrations across China during COVID-19 epidemic,indicating that coordinated control of other pollutants is needed.展开更多
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 ...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 24000 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.展开更多
Mineral dust comprises a great fraction of the global aerosol loading,but remains the largest uncertainty in predictions of the future climate due to its complexity in composition and physico-chemical properties.In th...Mineral dust comprises a great fraction of the global aerosol loading,but remains the largest uncertainty in predictions of the future climate due to its complexity in composition and physico-chemical properties.In this work,a case study characterizing Asian dust storm particles was conducted by multiple analysis methods,including SEM-EDS,XPS,FT-IR,BET,TPD/mass and Knudsen cell/mass.The morphology,elemental fraction,source distribution,true uptake coefficient for SO 2,and hygroscopic behavior were studied.The major components of Asian dust storm particles are aluminosilicate,SiO 2 and CaCO 3,with organic compounds and inorganic nitrate coated on the surface.It has a low reactivity towards SO 2 with a true uptake coefficient,5.767×10-6,which limits the conversion of SO 2 to sulfate during dust storm periods.The low reactivity also means that the heterogeneous reactions of SO 2 in both dry and humid air conditions have little effect on the hygroscopic behavior of the dust particles.展开更多
As an important precursor of hydroxyl radical, nitrous acid （HONO） plays a key role in the chemistry of the lower atmosphere. Recent atmospheric measurements and model calculations show strong enhancement for HONO f...As an important precursor of hydroxyl radical, nitrous acid （HONO） plays a key role in the chemistry of the lower atmosphere. Recent atmospheric measurements and model calculations show strong enhancement for HONO formation during daytime, while they are inconsistent with the known sources in the atmosphere, suggesting that current models are lacking important sources for HONO. In this article, heterogeneous photochemical reactions of nitric acid/nitrate anion and nitrogen oxide on various aerosols were reviewed and their potential contribution to HONO formation was also discussed. It is demonstrated that HONO can be formed by photochemical reaction on surfaces with deposited HNO3 , by photocatalytic reaction of NO2 on TiO2 or TiO2 -containing materials, and by photochemical reaction of NO2 on soot, humic acids or other photosensitized organic surfaces. Although significant uncertainties still exist in the exact mechanisms and the yield of HONO, these additional sources might explain daytime observations in the atmosphere.展开更多
Heterogeneous reactions of NO2 on different surfaces play an important role in atmospheric NOxremoval and HONO formation,having profound impacts on photochemistry in polluted urban areas.Previous studies have suggeste...Heterogeneous reactions of NO2 on different surfaces play an important role in atmospheric NOxremoval and HONO formation,having profound impacts on photochemistry in polluted urban areas.Previous studies have suggested that the NO2 uptake on the ground or aerosol surfaces could be a dominant source for elevated HONO during the daytime.However,the uptake behavior of NO2 varies with different surfaces,and different uptake coefficients were used or derived in different studies.To obtain a more holistic picture of heterogeneous NO2 uptake on different surfaces,a series of laboratory experiments using different flow tube reactors was conducted,and the NO2 uptake coefficients(γ)were determined on inorganic particles,sea water and urban grime.The results showed that heterogeneous reactions on those surfaces were generally weak in dark conditions,with the measuredγvaried from<10-8 to 3.2×10-7 under different humidity.A photo-enhanced uptake of NO2 on urban grime was observed,with the obvious formation of HONO and NO from the heterogeneous reaction.The photo-enhancedγwas measured to be 1.9×10-6 at 5%relative humidity(RH)and 5.8×10-6 at 70%RH on urban grime,showing a positive RH dependence for both NO2 uptake and HONO formation.The results demonstrate an important role of urban grime in the daytime NO2-to-HONO conversion,and could be helpful to explain the unknown daytime HONO source in the polluted urban area.展开更多
To investigate the sensitivity of secondary aerosol formation and oxidation capacity to NOx in homogeneous and heterogeneous reactions, a series of irradiated toluene/NOx/air and ?-pinene/NOx/air experiments were cond...To investigate the sensitivity of secondary aerosol formation and oxidation capacity to NOx in homogeneous and heterogeneous reactions, a series of irradiated toluene/NOx/air and ?-pinene/NOx/air experiments were conducted in smog chambers in the absence or presence of Al2O3 seed particles. Various concentrations of NOx and volatile organic compounds(VOCs) were designed to simulate secondary aerosol formation under different scenarios for NOx. Under "VOC-limited" conditions, the increasing NOx concentration suppressed secondary aerosol formation, while the increasing toluene concentration not only contributed to the increase in secondary aerosol formation, but also led to the elevated oxidation degree for the organic aerosol. Sulfate formation was suppressed with the increasing NOx due to a decreased oxidation capacity of the photooxidation system. Secondary organic aerosol(SOA) formation also decreased with the presence of high concentration of NOx, because organo-peroxy radicals(RO2) react with NOx instead of with peroxy radicals(RO2 or HO2), resulting in the formation of volatile organic products. The increasing concentration of NOx enhanced the formation of sulfate, nitrate and SOA under "NOx-limited" conditions, in which the heterogeneous reactions played an important role. In the presence of Al2O3 seed particles, a synergetic promoting effect of mineral dust and NOx on secondary aerosol formation in heterogeneous reactions was observed in the photooxidation. This synergetic effect strengthened the positive relationship between NOx and secondary aerosol formation under "NOx-limited" conditions but weakened or even overturned the negative relationship between NOx and secondary aerosol formation under "VOC-limited" conditions. Sensitivity of secondary aerosol formation to NOx seemed different in homogeneous and heterogeneous reactions, and should be both taken into account in the sensitivity study. The sensitivity of secondary aerosol formation to NOx was further investigated under "winter-like" and NH3-rich conditions. No obvious difference for the sensitivity of secondary aerosol formation except nitrate to NOx was observed.展开更多
Ammonium is an important atmospheric particulate component that dictates many environmental processes.The promotion of the heterogeneous conversion of NH_(3) to NH_(4)^(+) by SO_(2) on different mineral dust surfaces ...Ammonium is an important atmospheric particulate component that dictates many environmental processes.The promotion of the heterogeneous conversion of NH_(3) to NH_(4)^(+) by SO_(2) on different mineral dust surfaces displays remarkable discrepancies,especially on MgO and α-Fe2O3 surfaces,however,the underlying mechanisms are not well known.Here,using periodic density functional theory(DFT)calculation and Born-Oppenheimer molecular dynamics(BOMD)simulation,we explored the hetero-geneous adsorption of NH_(3) on MgO(110)and α--Fe2O3(001)surfaces in the presence and absence of SO_(2).The results show that on MgO(110)surface,hydrogen-bonding interactions of NH_(3) on both adsorbed hydroxyl or bisulfite/bisulfate sites are observed no matter whether SO_(2) is present or not.While,on theα-Fe2O3(001)surface,significant conversion of NH_(3) to NH_(4)^(+)occurs with the coexistence of SO_(2),which is due to the hydrogen transfer reaction from surface HSO4 to N in NH_(3).The fundamental reason may be that the stronger electron affinity of Fe3+than Mg2+results in adsorbed bisulfate and/or bisulfite with greater acidity on α-Fe2O3 surface than MgO surface.Our results give a molecular-level explanation for the heterogeneous conversion of NH_(3) to NH_(4)^(+)on different mineral dust surfaces under complex air pollution conditions.Considering the fact that ammonium is abundant in secondary particulates,this work would help in understanding the rapid conversion of ammonia to ammonium and in developing classification governance policies for the key precursor pollutants in China.展开更多
Nitrate is an important component of atmospheric particulate matter and affects air quality,climate,human health,and the ecosystem.Nitrate was previously considered a permanent sink for nitrogen oxides(NO_(x)).However...Nitrate is an important component of atmospheric particulate matter and affects air quality,climate,human health,and the ecosystem.Nitrate was previously considered a permanent sink for nitrogen oxides(NO_(x)).However,this viewpoint has been challenged in recent years because growing research evidence has shown the transformation of nitrate into NO_(x)(i.e.,renoxification).The photolysis of nitrate/HNO3,especially in the particulate phase or adsorbed on particles,can be a significant renoxification process in the atmosphere.The formation and photolysis of nitrate in aerosol not only change the diurnal variation of NO_(x),but also provide long-distance transport of NO_(x)in the form of nitrate,which affects local and regional atmospheric chemistry and air quality.This review summarizes recent advances in the fundamental understanding of the photolysis of nitrate/HNO3 under various atmospheric conditions,with a focus on mechanisms and key factors affecting the process.The atmospheric implications are discussed and future research is recommended.展开更多
Soot particles,composed of elemental carbon and organic compounds,have attracted widespread attention in recent years due to their significant impacts on climate,the environment and human health.Soot has been found to...Soot particles,composed of elemental carbon and organic compounds,have attracted widespread attention in recent years due to their significant impacts on climate,the environment and human health.Soot has been found to be chemically and physically active in atmospheric aging processes,which leads to alterations in its composition,morphology,hygroscopicity and optical properties and thus changes its environmental and health effects.The heterogeneous reactions on soot also have a significant impact on the transformation of gaseous pollutants into secondary aerosols.Therefore,the interactions between soot and atmospheric substances have been widely investigated to better understand the environmental behaviors of soot.In this review,we systematically summarize the progress and developments in the heterogeneous chemistry on soot over the past_(3)0 years.Atmospheric trace constituents such as NO_(2),O_(3),SO_(2),N_(2)O_(5),HNO_(3),H_(2)SO_(4),OH radical,HO_(2)radical,peroxyacetyl nitrate etc.,are presented in detail from the aspect of their heterogeneous reactions on soot.The possible mechanisms and the effects of environmental conditions on these heterogeneous reactions are also addressed.Further,the impacts of the heterogeneous reactions of soot on the atmospheric environment are discussed,and some aspects of soot-related research which require further investigation are proposed as well.展开更多
基金supported by the National Key R&D Program of China(No.2016YFC0202700)the National Natural Science Foundation of China(No.91543109 and 41877306)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Nos.XDB05040100,XDB05010300)the Youth Innovation Promotion Association,CAS(No.2018060)
文摘Current atmospheric quality models usually underestimate the level of ambient secondary organic aerosol(SOA), one of the possible reasons is that the precursors at different concentrations may undergo different oxidation processes and further affect SOA formation. Therefore, there is a need to perform more chamber studies to disclose the influence. In this work, SOA formation over a wide range of initial precursor concentrations(tens of ppb to hundreds of ppb levels) was investigated in a 30 m3 indoor smog chamber,and mainly through the analysis of multiple generations of VOCs detected from HR-To FPTRMS to expound the difference in the oxidation process between low and high precursor concentrations. Compared to high initial concentrations, gas-phase intermediates formed at low concentrations had a higher intensity by about one order of magnitude, and the lowvolatility compounds also had a higher formation potential due to the competition between semi-volatile intermediates and precursors with oxidants. In addition, the formed SOA was more oxidized with higher f44 value(0.14 ± 0.02) and more relevant to real atmosphere than that formed at high concentrations. This work should help to deeply understand SOA formation and improve the performance of air quality models for SOA simulation.
基金supported by the Key Research Program of Chinese Academy of Sciences (No. KJZD-EW-TZ-G06-01-15)the National Natural Science Foundation of China (No. 21407158)the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (No. XDB05010300)
文摘In order to evaluate the secondary aerosol formation potential at a suburban site of Beijing,in situ perturbation experiments in a potential aerosol mass（PAM） reactor were carried out in the winter of 2014.The variations of secondary aerosol formation as a function of time,OH exposure,and the concentrations of gas phase pollutants and particles were reported in this study.Two periods with distinct secondary aerosol formation potentials,marked as Period Ⅰ and Period Ⅱ,were identified during the observation.In Period Ⅰ,the secondary aerosol formation potential was high,and correlated well to the air pollutants,i.e.,SO2,NO2,and CO.The maximal secondary aerosol formation was observed with an aging time equivalent to about 3 days of atmospheric oxidation.In period Ⅱ,the secondary aerosol formation potential was low,with no obvious correlation with the air pollutants.Meanwhile,the aerosol mass decreased,instead of showing a peak,with increasing aging time.Backward trajectory analysis during the two periods confirmed that the air mass in Period Ⅰwas mainly from local sources,while it was attributed mostly to long distance transport in Period Ⅱ.The air lost its reactivity during the long transport and the particles became highly aged,resulting in a low secondary aerosol formation potential.Our experimental results indicated that the in situ measurement of the secondary aerosol formation potential could provide important information for evaluating the contributions of local emission and long distance transport to the aerosol pollution.
基金the support of the National Natural Science Foundation of China(NSFC)(Nos.52425003,22188102,and 52400144)the Project funded by China Postdoctoral Science Foundation(Nos.BX20220325 and 2023M743707)the Youth Innovation Promotion Association,CAS(Nos.Y2021020 and Y2022023).
文摘Air pollution is a major challenge to the improvement of urban environmental quality.The control of air pollution still faces severe challenges,especially in developing countries,such as ozone pollution control.Ozone is a typical secondary air pollutant,and its formation chemistry from its precursors(NOx and volatile organic compounds)is highly nonlinear,which caused the emission reduction of its precursors is not always effective and therefore new assisted approaches to control of ozone pollution are needed.Photocatalysis and ambient catalysis technology are expected to be applied in open atmosphere as a new booster to the direct purification of air pollutants in emission sources.In this perspective,we summarize the current knowledge about the photocatalysis and ambient catalysis technology for the removal of air pollutants under natural photothermal conditions.Based on these technologies,we propose the concept of“Environmental Catalytic City”,which refers to the spontaneous purification of low concentration urban air pollutants in the atmosphere by catalytic materials coating on the artificial surfaces,such as building surfaces in the city.In this way,the urban city with self-purification function can remove air pollution without additional energy consumption.The further improvement,development,and application of the“Environmental Catalytic City”is also discussed.
基金the National Natural Science Foundation of China(No.41877304)the National Key R&D Program of China(No.2018YFC0506901)the Youth Innovation Promotion Association,CAS(Nos.2018060 and 2018055)。
文摘The strict control measures and social lockdowns initiated to combat COVID-19 epidemic have had a notable impact on air pollutant concentrations.According to observation data obtained from the China National Environmental Monitoring Center,compared to levels in 2019,the average concentration of NO_(2) in early 2020 during COVID-19 epidemic has decreased by 53%,50%,and 30%in Wuhan city,Hubei Province(Wuhan excluded),and China(Hubei excluded),respectively.Simultaneously,PM_(2.5) concentration has decreased by 35%,29%,and 19%in Wuhan,Hubei(Wuhan excluded),and China(Hubei excluded),respectively.Less significant declines have also been found for SO_(2) and CO concentrations.We also analyzed the temporal variation and spatial distribution of air pollutant concentrations in China during COVID-19 epidemic.The decreases in PM_(2.5) and NO_(2) concentrations showed relatively consistent temporal variation and spatial distribution.These results support control of NO x to further reduce PM_(2.5) pollution in China.The concurrent decrease in NOx and PM_(2.5) concentrations resulted in an increase of O3 concentrations across China during COVID-19 epidemic,indicating that coordinated control of other pollutants is needed.
基金funded by the National Natural Science Foundation of China(Grant No.91844000)。
文摘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 24000 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.
基金supported by the National Natural Science Foundation of China (No. 21107129,20937004,50921064)
文摘Mineral dust comprises a great fraction of the global aerosol loading,but remains the largest uncertainty in predictions of the future climate due to its complexity in composition and physico-chemical properties.In this work,a case study characterizing Asian dust storm particles was conducted by multiple analysis methods,including SEM-EDS,XPS,FT-IR,BET,TPD/mass and Knudsen cell/mass.The morphology,elemental fraction,source distribution,true uptake coefficient for SO 2,and hygroscopic behavior were studied.The major components of Asian dust storm particles are aluminosilicate,SiO 2 and CaCO 3,with organic compounds and inorganic nitrate coated on the surface.It has a low reactivity towards SO 2 with a true uptake coefficient,5.767×10-6,which limits the conversion of SO 2 to sulfate during dust storm periods.The low reactivity also means that the heterogeneous reactions of SO 2 in both dry and humid air conditions have little effect on the hygroscopic behavior of the dust particles.
基金supported by the National Natural Science Foundation of China (No.21207145, 20937004)the Strategic Priority Research Program of the Chinese Academy of Sciences (No.XDB05050600)supported by the Special Co-construction Project of the Beijing Municipal Commission of Education
文摘As an important precursor of hydroxyl radical, nitrous acid （HONO） plays a key role in the chemistry of the lower atmosphere. Recent atmospheric measurements and model calculations show strong enhancement for HONO formation during daytime, while they are inconsistent with the known sources in the atmosphere, suggesting that current models are lacking important sources for HONO. In this article, heterogeneous photochemical reactions of nitric acid/nitrate anion and nitrogen oxide on various aerosols were reviewed and their potential contribution to HONO formation was also discussed. It is demonstrated that HONO can be formed by photochemical reaction on surfaces with deposited HNO3 , by photocatalytic reaction of NO2 on TiO2 or TiO2 -containing materials, and by photochemical reaction of NO2 on soot, humic acids or other photosensitized organic surfaces. Although significant uncertainties still exist in the exact mechanisms and the yield of HONO, these additional sources might explain daytime observations in the atmosphere.
基金supported by the French National Research Agency/Research Grants Council of Hong Kong Special Administrative Region,China(ANR/RGC)Joint Research Scheme(project A-PolyU502/16-SEAM)National Natural Science Foundation of China(Nos.91744204,91844301)+1 种基金the Research Grants Council of Hong Kong Special Administrative Region,China(Nos.T24/504/17,15265516,C5022-14G)。
文摘Heterogeneous reactions of NO2 on different surfaces play an important role in atmospheric NOxremoval and HONO formation,having profound impacts on photochemistry in polluted urban areas.Previous studies have suggested that the NO2 uptake on the ground or aerosol surfaces could be a dominant source for elevated HONO during the daytime.However,the uptake behavior of NO2 varies with different surfaces,and different uptake coefficients were used or derived in different studies.To obtain a more holistic picture of heterogeneous NO2 uptake on different surfaces,a series of laboratory experiments using different flow tube reactors was conducted,and the NO2 uptake coefficients(γ)were determined on inorganic particles,sea water and urban grime.The results showed that heterogeneous reactions on those surfaces were generally weak in dark conditions,with the measuredγvaried from<10-8 to 3.2×10-7 under different humidity.A photo-enhanced uptake of NO2 on urban grime was observed,with the obvious formation of HONO and NO from the heterogeneous reaction.The photo-enhancedγwas measured to be 1.9×10-6 at 5%relative humidity(RH)and 5.8×10-6 at 70%RH on urban grime,showing a positive RH dependence for both NO2 uptake and HONO formation.The results demonstrate an important role of urban grime in the daytime NO2-to-HONO conversion,and could be helpful to explain the unknown daytime HONO source in the polluted urban area.
基金supported by the National Natural Science Foundation of China(21407158)the"Strategic Priority Research Program"of the Chinese Academy of Sciences(XDB05010300,XDB05040100,XDB05010200)
文摘To investigate the sensitivity of secondary aerosol formation and oxidation capacity to NOx in homogeneous and heterogeneous reactions, a series of irradiated toluene/NOx/air and ?-pinene/NOx/air experiments were conducted in smog chambers in the absence or presence of Al2O3 seed particles. Various concentrations of NOx and volatile organic compounds(VOCs) were designed to simulate secondary aerosol formation under different scenarios for NOx. Under "VOC-limited" conditions, the increasing NOx concentration suppressed secondary aerosol formation, while the increasing toluene concentration not only contributed to the increase in secondary aerosol formation, but also led to the elevated oxidation degree for the organic aerosol. Sulfate formation was suppressed with the increasing NOx due to a decreased oxidation capacity of the photooxidation system. Secondary organic aerosol(SOA) formation also decreased with the presence of high concentration of NOx, because organo-peroxy radicals(RO2) react with NOx instead of with peroxy radicals(RO2 or HO2), resulting in the formation of volatile organic products. The increasing concentration of NOx enhanced the formation of sulfate, nitrate and SOA under "NOx-limited" conditions, in which the heterogeneous reactions played an important role. In the presence of Al2O3 seed particles, a synergetic promoting effect of mineral dust and NOx on secondary aerosol formation in heterogeneous reactions was observed in the photooxidation. This synergetic effect strengthened the positive relationship between NOx and secondary aerosol formation under "NOx-limited" conditions but weakened or even overturned the negative relationship between NOx and secondary aerosol formation under "VOC-limited" conditions. Sensitivity of secondary aerosol formation to NOx seemed different in homogeneous and heterogeneous reactions, and should be both taken into account in the sensitivity study. The sensitivity of secondary aerosol formation to NOx was further investigated under "winter-like" and NH3-rich conditions. No obvious difference for the sensitivity of secondary aerosol formation except nitrate to NOx was observed.
基金supported by National Natural Science Foundation of China(grant Nos.22006158,22188102 and 221222610)the China Postdoctoral Science Foundation(grant Nos.2019M660818 and 2020TQ0339)Special Research Assistant Project of the Chinese Academy of Sciences.
文摘Ammonium is an important atmospheric particulate component that dictates many environmental processes.The promotion of the heterogeneous conversion of NH_(3) to NH_(4)^(+) by SO_(2) on different mineral dust surfaces displays remarkable discrepancies,especially on MgO and α-Fe2O3 surfaces,however,the underlying mechanisms are not well known.Here,using periodic density functional theory(DFT)calculation and Born-Oppenheimer molecular dynamics(BOMD)simulation,we explored the hetero-geneous adsorption of NH_(3) on MgO(110)and α--Fe2O3(001)surfaces in the presence and absence of SO_(2).The results show that on MgO(110)surface,hydrogen-bonding interactions of NH_(3) on both adsorbed hydroxyl or bisulfite/bisulfate sites are observed no matter whether SO_(2) is present or not.While,on theα-Fe2O3(001)surface,significant conversion of NH_(3) to NH_(4)^(+)occurs with the coexistence of SO_(2),which is due to the hydrogen transfer reaction from surface HSO4 to N in NH_(3).The fundamental reason may be that the stronger electron affinity of Fe3+than Mg2+results in adsorbed bisulfate and/or bisulfite with greater acidity on α-Fe2O3 surface than MgO surface.Our results give a molecular-level explanation for the heterogeneous conversion of NH_(3) to NH_(4)^(+)on different mineral dust surfaces under complex air pollution conditions.Considering the fact that ammonium is abundant in secondary particulates,this work would help in understanding the rapid conversion of ammonia to ammonium and in developing classification governance policies for the key precursor pollutants in China.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.22188102 and 21922610)The authors appreciate the Ozone Formation Mechanism and Control Strategies Project of the Research Center for Eco-Environmental Sciences,CAS(China)(No.RCEES-CYZX-2020)+1 种基金the Cultivating Project of Strategic Priority Research Program of Chinese Academy of Sciences(China)(No.XDPB1901)the Young Talent Project of the Center for Excellence in Regional Atmospheric Environment,CAS(China)(No.CERAE201801).
文摘Nitrate is an important component of atmospheric particulate matter and affects air quality,climate,human health,and the ecosystem.Nitrate was previously considered a permanent sink for nitrogen oxides(NO_(x)).However,this viewpoint has been challenged in recent years because growing research evidence has shown the transformation of nitrate into NO_(x)(i.e.,renoxification).The photolysis of nitrate/HNO3,especially in the particulate phase or adsorbed on particles,can be a significant renoxification process in the atmosphere.The formation and photolysis of nitrate in aerosol not only change the diurnal variation of NO_(x),but also provide long-distance transport of NO_(x)in the form of nitrate,which affects local and regional atmospheric chemistry and air quality.This review summarizes recent advances in the fundamental understanding of the photolysis of nitrate/HNO3 under various atmospheric conditions,with a focus on mechanisms and key factors affecting the process.The atmospheric implications are discussed and future research is recommended.
基金This work was financially supported by the National Natural Science Foundation of China(22122610,22188102,41877304,21777171).
文摘Soot particles,composed of elemental carbon and organic compounds,have attracted widespread attention in recent years due to their significant impacts on climate,the environment and human health.Soot has been found to be chemically and physically active in atmospheric aging processes,which leads to alterations in its composition,morphology,hygroscopicity and optical properties and thus changes its environmental and health effects.The heterogeneous reactions on soot also have a significant impact on the transformation of gaseous pollutants into secondary aerosols.Therefore,the interactions between soot and atmospheric substances have been widely investigated to better understand the environmental behaviors of soot.In this review,we systematically summarize the progress and developments in the heterogeneous chemistry on soot over the past_(3)0 years.Atmospheric trace constituents such as NO_(2),O_(3),SO_(2),N_(2)O_(5),HNO_(3),H_(2)SO_(4),OH radical,HO_(2)radical,peroxyacetyl nitrate etc.,are presented in detail from the aspect of their heterogeneous reactions on soot.The possible mechanisms and the effects of environmental conditions on these heterogeneous reactions are also addressed.Further,the impacts of the heterogeneous reactions of soot on the atmospheric environment are discussed,and some aspects of soot-related research which require further investigation are proposed as well.
