Progress in quantitative research on the relationship between atmospheric oxidation and air quality

Atmospheric oxidizing capacity(AOC)is an essential driving force of troposphere chemistry and self-cleaning,but the definition of AOC and its quantitative representation remain uncertain.Driven by national demand for air pollution control in recent years,Chinese scholars have carried out studies on theories of atmospheric chemistry and have made considerable progress in AOC research.This paper will give a brief review of these developments.First,AOC indexes were established that represent apparent atmospheric oxidizing ability(AOIe)and potential atmospheric oxidizing ability(AOIp)based on aspects of macrothermodynamics and microdynamics,respectively.A closed study refined the quantitative contributions of heterogeneous chemistry to AOC in Beijing,and these AOC methods were further applied in Beijing-Tianjin-Hebei and key areas across the country.In addition,the detection of ground or vertical profiles for atmospheric OH·,HO_(2)·,NO_(3)·radicals and reservoir molecules can now be obtained with domestic instruments in diverse environments.Moreover,laboratory smoke chamber simulations revealed heterogeneous processes involving reactions of O_(3)and NO_(2),which are typical oxidants in the surface/interface atmosphere,and the evolutionary and budgetary implications of atmospheric oxidants reacting under multispecies,multiphase and multi-interface conditions were obtained.Finally,based on the GRAPES-CUACE adjoint model improved by Chinese scholars,simulations of key substances affecting atmospheric oxidation and secondary organic and inorganic aerosol formation have been optimized.Normalized numerical simulations of AOIe and AOIp were performed,and regional coordination of AOC was adjusted.An optimized plan for controlling O_(3)and PM2.5was analyzed by scenario simulation.

Characterizing oxygenated volatile organic compounds and their sources in rural atmospheres in China

Oxygenated volatile organic compounds(OVOCs) are important precursors and products of atmospheric secondary pollution. The sources of OVOCs, however, are still quite uncertain,especially in the atmosphere with much pollution in China. To study the sources of OVOCs in rural atmospheres, a proton transfer reaction mass spectrometry(PTR-MS) was deployed at a northern rural site(WD) and a southern rural site(YMK) in China during the summer of 2014 and 2016, respectively. The continuous observation showed that the mean concentration of TVOCs(totally 17 VOCs) measured at WD(52.4 ppbv) was far higher than that at YMK(11.1 ppbv), and the OVOCs were the most abundant at both the two sites. The diurnal variations showed that local sources of OVOCs were still prominent at WD, while regional transport influenced YMK much. The photochemical age-based parameterization method was then used to quantitatively apportion the sources of ambient OVOCs. The anthropogenic primary sources at WD and YMK contributed less(2%–16%) to each OVOC species. At both the sites, the atmospheric background had a dominant contribution(～ 50%) to acetone and formic acid, while the anthropogenic secondary formation was the main source(～ 40%) of methanol and MEK. For acetaldehyde and acetic acid, the biogenic sources were their largest source(～ 40%) at WD, while the background(39%) and anthropogenic secondary formation(42%) were their largest sources at YMK, respectively. This study reveals the complexity of sources of OVOCs in China, which urgently needs explored further.

Understanding primary and secondary sources of ambient oxygenated volatile organic compounds in Shenzhen utilizing photochemical age-based parameterization method

Oxygenated volatile organic compounds(OVOCs) are key intermediates in the atmospheric photooxidation process. To further study the primary and secondary sources of OVOCs,their ambient levels were monitored using a proton-transfer reaction mass spectrometer(PTR-MS) at an urban site in the Pearl River Delta of China. Continuous monitoring campaigns were conducted in the spring, summer, fall, and winter of 2016. Among the six types of OVOC species, the mean concentrations of methanol were the highest in each season(up to 13–20 ppbv), followed by those of acetone, acetaldehyde and acetic acid(approximately 2–4 ppbv), while those of formic acid and methyl ethyl ketone(MEK) were the lowest(approximately 1–2 ppbv). As observed from a diurnal variation chart, the OVOCs observed in Shenzhen may have been affected by numerous factors such as their primary and secondary sources and photochemical consumption. The photochemical age-based parameterization method was used to apportion the sources of ambient OVOCs. Methanol had significant anthropogenic primary sources but negligible anthropogenic secondary sources during all of the seasons. Acetone, MEK and acetic acid were mostly attributed to anthropogenic primary sources during each season with smaller contributions from anthropogenic secondary sources. Acetaldehyde had similar contributions from both anthropogenic secondary and anthropogenic primary sources throughout the year.Meanwhile, anthropogenic primary sources contributed the most to formic acid.

Characterization of submicron aerosols in the urban outflow of the central Pearl River Delta region of China

Submicron aerosol particles （with aerody- namic diameters less than 1 pm, PM1） were sampled and measured in Heshan, an urban outflow site of Guangzhou megacity in Pearl River Delta in South China, using an Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer （HR-ToF-AMS） in November 2010 during 2010 Guangzhou Asian Games. The mean PM~ mass concentration measured was 47.9 ± 17.0 μg.m3 during the campaign, with organic aerosol （OA） and sulfate being the two dominant species, accounting for 36.3% and 20.9% of the total mass, respectively, followed by black carbon （17.1%, measured by an aethalometer）, nitrate （12.9%）, ammonium （9.6%） and chloride （3.1%）. The average size distributions of the species （except black carbon） were dominated by an accumulation mode peaking at -550 nm. Calculations based on high-resolution organic mass spectrum showed that, C, H, O and N on average contributed 58.1%, 7.3%, 30.7%, and 3.9% to the total organic mass, respectively. The average ratio of organic mass over organic carbon mass （OM/OC） was 1.73 ± 0.08. Four components of OA were identified by the Positive Matrix Factorization （PMF） analysis, including a hydro- carbon-like （HOA）, a biomass burning （BBOA） and two oxygenated （SV-OOA and LV-OOA） organic aerosol components, which on average accounted for 18.0%, 14.3%, 28.8% and 38.9% of the total organic mass, respectively.

Source apportionment of PM_(2.5)light extinction in an urban atmosphere in China

Haze in China is primarily caused by high pollution of atmospheric fine particulates（PM2.5）.However, the detailed source structures of PM2.5 light extinction have not been well established, especially for the roles of various organic aerosols, which makes haze management lack specified targets. This study obtained the mass concentrations of the chemical compositions and the light extinction coefficients of fine particles in the winter in Dongguan, Guangdong Province, using high time resolution aerosol observation instruments. We combined the positive matrix factor（PMF） analysis model of organic aerosols and the multiple linear regression method to establish a quantitative relationship model between the main chemical components, in particular the different sources of organic aerosols and the extinction coefficients of fine particles with a high goodness of fit（R^2= 0.953）. The results show that the contribution rates of ammonium sulphate,ammonium nitrate, biomass burning organic aerosol（BBOA）, secondary organic aerosol（SOA） and black carbon（BC） were 48.1%, 20.7%, 15.0%, 10.6%, and 5.6%, respectively. It can be seen that the contribution of the secondary aerosols is much higher than that of the primary aerosols（79.4% versus 20.6%） and are a major factor in the visibility decline. BBOA is found to have a high visibility destroying potential, with a high mass extinction coefficient, and was the largest contributor during some high pollution periods. A more detailed analysis indicates that the contribution of the enhanced absorption caused by BC mixing state was approximately 37.7% of the total particle absorption and should not be neglected.

Characterization of particle number size distribution and new particle formation in Southern China

Knowledge of particle number size distribution（PND） and new particle formation（NPF）events in Southern China is essential for mitigation strategies related to submicron particles and their effects on regional air quality,haze,and human health.In this study,seven field measurement campaigns were conducted from December 2013 to May 2015 using a scanning mobility particle sizer（SMPS） at four sites in Southern China,including three urban sites and one background site.Particles were measured in the size range of15-515 nm,and the median particle number concentrations（PNCs） were found to vary in the range of 0.3× 10~4-2.2 × 10~4 cn^（-3） at the urban sites and were approximately 0.2 × 10~4 cm^（-3） at the background site.The peak diameters at the different sites varied largely from 22 to 102 nm.The PNCs in the Aitken mode（25-100 nm） at the urban sites were up to 10 times higher than they were at the background site,indicating large primary emissions from traffic at the urban sites.The diurnal variations of PNCs were significantly influenced by both rush hour traffic at the urban sites and NPF events.The frequencies of NPF events at the different sites were0%-30%,with the highest frequency occurring at an urban site during autumn.With higher SO_2 concentrations and higher ambient temperatures being necessary,NPF at the urban site was found to be more influenced by atmospheric oxidizing capability,while NPF at the background site was limited by the condensation sink.This study provides a unique dataset of particle number and size information in various environments in Southern China,which can help understand the sources,formation,and the climate forcing of aerosols in this quickly developing region,as well as help constrain and validate NPF modeling.

Chemical characterization and source apportionment of atmospheric submicron particles on the western coast of Taiwan Strait, China

Taiwan Strait is a special channel for subtropical East Asian Monsoon and its western coast is an important economic zone in China. In this study, a suburban site in the city of Xiamen on the western coast of Taiwan Strait was selected for fine aerosol study to improve the understanding of air pollution sources in this region. An Aerodyne high-resolution time-of-flight aerosol mass spectrometer（HR-To F-AMS） and an Aethalometer were deployed to measure fine aerosol composition with a time resolution of 5 min from May 1to 18, 2015. The average mass concentration of PM1 was 46.2 ± 26.3 μg/m^3 for the entire campaign. Organics（28.3%）, sulfate（24.9%）, and nitrate（20.6%） were the major components in the fine particles, followed by ammonium, black carbon（BC）, and chloride. Evolution of nitrate concentration and size distribution indicated that local NOx emissions played a key role in high fine particle pollution in Xiamen. In addition, organic nitrate was found to account for 9.0%–13.8% of the total measured nitrate. Positive Matrix Factorization（PMF）conducted with high-resolution organic mass spectra dataset differentiated the organic aerosol into three components, including a hydrocarbon-like organic aerosol（HOA） and two oxygenated organic aerosols（SV-OOA and LV-OOA）, which on average accounted for 27.6%,28.8%, and 43.6% of the total organic mass, respectively. The relationship between the mass concentration of submicron particle species and wind further confirmed that all major fine particle species were influenced by both strong local emissions in the southeastern area of Xiamen and regional transport through the Taiwan Strait.

老化过程对大气黑碳颗粒物性质及其气候效应的影响

黑碳颗粒物是人类活动排放到大气中的重要温室物种,但对其气候效应的认知仍然存在很大的不确定性.老化过程对黑碳颗粒物性质的改变,是造成这种不确定性的重要来源.针对黑碳老化这一研究热点,本文综述了国内外基于实验室和外场研究的进展,从影响黑碳微观性质的角度出发,总结梳理了老化过程对黑碳混合态,包括形貌和化学组分的影响,并在此基础上,探讨了与气候效应相关的黑碳颗粒物的吸光性、吸湿性、云凝结核与冰核活性在老化过程中的变化.伴随着老化过程的进行,黑碳颗粒物由初始的外混态向内混态转变,形貌由枝杈状结构经填充-塌缩-持续被包裹的过程逐渐演变成近似球形的核壳结构.黑碳颗粒物中的化学组分在排放初期会受到共同排放组分的影响,并在老化过程中表现出二次组分增加的趋势.由于包裹物在黑碳外层的累积,老化过程会导致黑碳颗粒物吸光性的增强,但增强倍数受到包裹物厚度、形貌和化学组分的共同影响.并且,在讨论颗粒物群体的吸光增强倍数时,黑碳颗粒物之间混合态的非均一性也需要纳入考虑.老化过程会增强黑碳颗粒物的吸湿性与云凝结核活性,这与包裹物本身的性质密切相关,但相关的外场研究还十分缺乏.针对黑碳颗粒物是否具有冰核活性以及老化过程是否会改变其活性的问题,现有研究仍然没有定论.在此基础上,本文提出了黑碳老化未来的研究方向:探究真实燃烧条件下不同来源黑碳颗粒物的理化特性与老化特征;在不同大气环境中开展综合观测,识别出复杂大气条件下影响黑碳老化的关键因素;推动黑碳老化促进区域大气污染的机制研究;加强黑碳颗粒物与间接气候效应相关的性质研究.

大气气溶胶液态水中二次有机气溶胶生成机制研究进展

大气二次有机气溶胶是PM2.5的主要组分,具有重要的环境和气候效应.在其主要生成途径中,气溶胶液态水中的液相生成是当前大气化学研究领域的前沿科学问题之一.液相二次有机气溶胶(aqueous secondary organic aerosol, aqSOA)前体物通过摄取进入湿气溶胶后,参与气溶胶内部的液相反应,生成有机硫、有机氮等aqSOA.本文对aqSOA前体物的摄取过程、生成的化学机制以及当前主要的研究手段进行详细总结,并对该领域未来研究进行展望. aqSOA前体物的摄取受到相对湿度、气溶胶水溶性等因素的影响,从而影响其进入气溶胶的后续反应.aqSOA生成的化学机制可分为自由基反应和非自由基反应,其中,自由基反应以OH自由基液相化学为主;非自由基反应则多为羰基化合物的液相反应.近年来,先进的离线和在线质谱技术的发展推动了对实际环境大气中aqSOA生成机制的认识,并从分子层面识别出aqSOA产物,但aqSOA生成的大气化学过程仍未明晰.未来研究中,开发新的分析技术,扩充aqSOA反应动力学数据库,进一步完善模型模拟,为aqSOA生成研究提供新思路.

Development of an on-line measurement system for water-soluble organic matter in PM_(2.5) and its application in China

Water-soluble organic matter（WSOM） represents a critical fraction of fine particles（PM2.5）in the air, but its changing behaviors and formation mechanisms are not well understood yet, partly due to the lack of fast techniques for the ambient measurements. In this study,a novel system for the on-line measurement of water-soluble components in PM2.5, the particle-into-liquid sampler（PILS）–Nebulizer–aerosol chemical speciation monitor（ACSM）, was developed by combining a PILS, a nebulizer, and an ACSM. High time resolution concentrations of WSOM, sulfate, nitrate, ammonium, and chloride, as well as mass spectra, can be obtained with satisfied quality control results. The system was firstly applied in China for field measurement of WSOM. The mass spectrum of WSOM was found to resemble that of oxygenated organic aerosol, and WSOM agreed well with secondary inorganic ions. All evidence collected in the field campaign demonstrated that WSOM could be a good surrogate of secondary organic aerosol（SOA）. The PILS–Nebulizer–ACSM system can thus be a useful tool for intensive study of WSOM and SOA in PM2.5.

High-performance modified uni-traveling carrier photodiode integrated on a thin-film lithium niobate platform

Lithium niobate on insulator(LNOI)has become an intriguing platform for integrated photonics for applications in communications,microwave photonics,and computing.Whereas,integrated devices including modulators,resonators,and lasers with high performance have been recently realized on the LNOI platform,high-speed photodetectors,an essential building block in photonic integrated circuits,have not been demonstrated on LNOI yet.Here,we demonstrate for the first time,heterogeneously integrated modified uni-traveling carrier photodiodes on LNOI with a record-high bandwidth of 80 GHz and a responsivity of 0.6 A/W at a 1550-nm wavelength.The photodiodes are based on an n-down In GaAs/InP epitaxial layer structure that was optimized for high carrier transit time-limited bandwidth.Photodiode integration was achieved using a scalable wafer die bonding approach that is fully compatible with the LNOI platform.

Secondary organic aerosol formation from straw burning using an oxidation flow reactor

Herein,we use an oxidation flow reactor,Gothenburg:Potential Aerosol Mass(Go:PAM)reactor,to investigate the secondary organic aerosol(SOA)formation from wheat straw burning.Biomass burning emissions are exposed to high concentrations of hydroxyl radicals(OH)to simulate processes equivalent to atmospheric oxidation of 0-2.55 days.Primary volatile organic compounds(VOCs)were investigated,and particles were measured before and after the Go:PAM reactor.The influence of water content(i.e.5%and 11%)in wheat straw was also explored.Two burning stages,the flaming stage,and non-flaming stages,were identified.Primary particle emission factors(EFs)at a water content of 11%(~3.89 g/kg-fuel)are significantly higher than those at a water content of 5%(~2.26 g/kg-fuel)during the flaming stage.However,the water content showed no significant influence at the non-flaming stage.EFs of aromatics at a non-flaming stage(321.8±46.2 mg/kg-fuel)are larger than that at a flaming stage(130.9±37.1 mg/kg-fuel).The OA enhancement ratios increased with the increase in OH exposure at first and decreased with the additional increment of OH exposure.The maximum OA enhancement ratio is~12 during the non-flaming stages,which is much higher than~1.7 during the flaming stages.The mass spectrum of the primary wheat burning organic aerosols closely resembles that of resolved biomass burning organic aerosols(BBOA)based on measurements in ambient air.Our results show that large gap(0%-90%)still remains to estimate biomass burning SOA if only the oxidation of VOCs were included.

Spectral control of nonclassical light pulses using an integrated thin-film lithium niobate modulator

Manipulating the frequency and bandwidth of nonclassical light is essential for implementing frequency-encoded/multiplexed quantum computation,communication,and networking protocols,and for bridging spectral mismatch among various quantum systems.However,quantum spectral control requires a strong nonlinearity mediated by light,microwave,or acoustics,which is challenging to realize with high efficiency,low noise,and on an integrated chip.Here,we demonstrate both frequency shifting and bandwidth compression of heralded single-photon pulses using an integrated thin-film lithium niobate(TFLN)phase modulator.We achieve record-high electro-optic frequency shearing of telecom single photons over terahertz range(±641 GHz or±5.2 nm),enabling high visibility quantum interference between frequency-nondegenerate photon pairs.We further operate the modulator as a time lens and demonstrate over eighteen-fold(6.55 nm to 0.35 nm)bandwidth compression of single photons.Our results showcase the viability and promise of on-chip quantum spectral control for scalable photonic quantum information processing.