Analysis of aerosol ammonium nitrate: Departures from equilibrium during SCAQS

The size distribution of the inorganic components of atmospheric aerosols measured during the 1987 Southern California Air Quality Study (SCAQS) are used to investigate the hypothesis that transport limits equilibration of gas- and aerosol-phase ammonium nitrate and influences their size distribution. Estimates of the equilibration time constants at four sites in southern California show a wide range of values; at small values equilibrium is expected whereas at large values departures from equilibrium are expected. An equilibrium indicator is proposed based on the size distributions of aerosol ammonium and nitrate that shows when particles of different size are in mutual equilibrium with respect to ammonium nitrate. Values of the indicator range from unity, demonstrating equilibrium, to less than 0.5, demonstrating that different size particles are not in mutual equilibrium. Comparison of the time constant values to the equilibrium indicator values show a significant correlation, so it is concluded that different size aerosol particles are often not in mutual equilibrium due to transport limitations, supporting the hypothesis. It is concluded that both thermodynamics and mass transport must be considered to predict accurately the size distribution of the volatile inorganics in atmospheric aerosol.     

Kinetic and thermodynamic behaviour of volatile ammonium compounds in industrial and marine atmospheres

Measurements of volatile ammonium aerosol compounds and respective acidic and basic gaseous precursors were taken at an industrial site emitting HCl, HNO₃ and NH₃ and at a marine suburban location.Because of fresh industrial emissions the gaseous acid and base concentration products show values orders of magnitude higher than thermodynamic equilibrium previsions, at the industrial site. To our knowledge these are the first published field measurements that strongly confirm that gas-particle equilibrium conditions are not attained instantaneously in the atmosphere and that kinetic constraints play an important role on gas-particle conversion for ammonium chloride and ammonium nitrate compounds. The results permit to conclude that, for temperature conditions lower than 15°C, transformation rates are not high, several minutes being necessary, at least, for the equilibrium between gaseous precursors and ammonium particulate products to be reached.At the marine suburban location a diurnal variation was observed for gaseous and particulate compounds in agreement with known emission and transformation mechanisms. The behaviour of nitric and hydrochloric acids in the marine atmosphere can be better explained if kinetic limitations are considered for the reaction of HNO₃ with NaCl aerosol particles and for the transference of acids and ammonia to the particulate phase.     

Second-generation inorganic aerosol model

Accurate prediction of the size distribution of the inorganic components of atmospheric aerosols must account for both therthermodynamic properties of the aerosol particles and transport between the gas and aerosol phases. For volatile inorganic species the transport rate is governed by the particle surface partial pressures which, in turn, is determined by the phase state and composition of the aerosol. We develop a model of the temporal composition of atmospheric aerosol particles based on their transport and thermodynamic properties. Included in the model is an improved theory of the temperature and composition dependence of deliquescence. Components of the model are tested against measurements of activity coefficients in single- and multicomponent aqueous solutions and general agreement is found. Aerosol water predictions are significantly higher under conditions of low relative humidity due to the improved theory of deliquescence.     

Determination of aerosol strong acidity losses due to interactions of collected particles: Results from laboratory and field studies

Existing methods of measuring atmospheric aerosol strong acidity adequately prevent neutralization of fine-particle acidity by removing course alkaline particles and gaseous ammonia from air samples. However, these techniques do not consider particle interactions on the collection medium; therefore, they may still underestimate the actual aerosol acidity. Assessment of acid neutralization due to such interactions is made possible using annular denuder technology in conjuction with a newly designed filter pack. The amount of sulfate-related acidity neutralized by the collected ammonium nitrate (and possibly ammonium chloride and organic acid ammonium salts) is determined. Laboratory data suggest that large fractions of sulfate-related aerosol acidity are neutralized by ammonium nitrate particles during collection on filter media. Field data from the Harvard Acid Aerosol Health Effects Study also suggest that ammonium nitrate and possibly other ammonium salts, such as ammonium chloride, neutralize collected acid aerosols. For low-acid aerosol concentrations, the correction factor is significant; whereas, for high-acid concentrations, correction is negligible.     

Hydrochloric acid: A regional perspective on concentrations and formation in the atmosphere of Southern California

Atmospheric gaseous hydrochloric acid (HCl) concentrations and water-soluble species in the aerosol phase were measured at nine sites in Southern California throughout the year 1986. Annual average HCl concentrations measured by the denuder difference method ranged from 0.39 ppb at an offshore island to 1.25 ppb onshore at Hawthorne, California. An ion balance on the aerosol shows that coarse particle chloride begins as sea salt over the ocean and is depleted relative to aerosol sodium with transport inland. Total chloride and sodium balances show that chloride depletion from the aerosol is matched by a comparable increase in gaseous HCl concentrations, consistent with the proposition that acid gas reactions with sea salt are the principal source of gaseous HCl in the Southern California atmosphere. Fine aerosol chloride exceeds fine particle sodium on a number of occasions, particularly at one inland site known for extraordinarily high NH₃ levels. There is evidence that coarse aerosol chloride from sea salt is being processed by atmospheric reactions through HCl to form fine aerosol, possibly NH₄Cl.     

A numerical simulation of kinetic constraints upon achievement of the ammonium nitrate dissociation equilibrium in the troposphere

Various mechanisms and associated rate expressions for the reversible evaporation of volatile ammonium salts are presented, and experimental evidence for them discussed. The literature concerned with the existence of stable NH₄⁺ salt monomers in the gas phase in highlighted. Four kinetic mechanisms are presented: monomer formation; adsorption of one precursor species on the particle surface; biomolecular surface reaction; and transport-limited particle growth. No mechanism emerges as the rate-limiting process for all experimental studies. Rate constant ratios for the first two mechanisms are calculated from the literature and shown to differ greatly from the thermodynamic equilibrium constant.A simple box model is developed to determine the importance of kinetic constraints on aerosol growth and evaporation in the tropospheric boundary layer. No attempt is made to model actual tropospheric processes other than the daytime oxidation of NO₂ and the kinetics of aerosol growth itself, so that model output is representative rather than definitive.Substantial departures from equilibrium are seen, giving gas concentration products ranging from −200 to 5000% of the theoretical value, Ke. At low temperatures and high relative humidities (r.h.) a large proportion of the potential condensable NO₃⁻ remains in the gas phase. The behaviour is general over a range of initial aerosol loadings, temperatures, r.h. and model formulations. Both pure NH₄NO₃ aerosol and a hypothetical equimolar mixture with (NH₄)₂SO₄, conform to the general case.     

Second organic aerosol formation from the ozonolysis of α-pinene in the presence of dry submicron ammonium sulfate aerosol

An indoor chamber facility is described for investigation of atmospheric aerosol chemistry. Two sets of α-pinene ozonolysis experiments were conducted in the presence of dry ammonium sulfate seed particle: ozone limited experiments and α-pinene limited experiments. The concentration of gas phase and particle phase species was monitored continuously by on-line instruments and recorded automatically by data sampling system. The evolution of size distribution was measured by a scanning mobility particle sizer ...     

Second organic aerosol formation from the ozonolysis of -pinene in the presence of dry submicron ammonium sulfate aerosol

An indoor chamber facility is described for investigation of atmospheric aerosol chemistry. Two sets of α-pinene ozonolysisexperiments were conducted in the presence of dry ammonium sulfate seed particle: ozone limited experiments and α-pinene limitedexperiments. The concentration of gas phase and particle phase species was monitored continuously by on-line instruments andrecorded automatically by data sampling system. The evolution of size distribution was measured by a scanning mobility particlesizer (SMPS), and α-pinene consumed was measured using GC-FID. Secondary organic aerosol (SOA) produced for seed-free systemis 100% organic in content, resulting from a sufficient supersaturation of low volatility organics to produce homogeneous nucleationfollowed by condensation to the aerosol. Secondary organic aerosol produced in seeded system is a mixture of organic and inorganicconstituents, initially forms via condensation onto the inorganic particles, and subsequent growth occurs via absorption into the organicsurface coating the inorganic core. Although the formation process and the size distribution for seed-free system and seeded system isdifferent, the ultimate mass of SOA formed is equal, and SOA yield for the two system located in the same regression line when usingone-product model, suggesting that the presence of dry ammonium sulfate seed has no measurable effect on the total aerosol yield, and the dry seed particle acts solely as a site upon which organic deposition occurs.     

南京北郊大气气溶胶的吸湿性观测研究

大气气溶胶的吸湿性不仅影响气溶胶的光学特性进而影响大气能见度,并且影响气溶胶的直接和间接气候效应.本文利用加湿串联差分迁移分析仪H-TDMA,于2012年5~7月在南京地区,对40~200nm大气气溶胶粒子在不同相对湿度下的吸湿增长因子进行了观测研究.统计结果表明:在90%相对湿度下,颗粒物的吸湿增长因子GF多为双峰分布,分为GF1.15的强吸湿组分.弱吸湿组分的吸湿增长因子(GFLH)在1.10~1.14之间;对应的强吸湿组分增长因子(GFMH )范围在1.47~1.58之间变化.相同粒径下的离散程度(σ)强吸湿组大于弱吸湿组,说明强吸湿组的粒子化学成分更复杂,异质性更强.相对湿度的变化对粒子吸湿增长的影响与粒子大小及化学组分有关,爱根核模态和积聚模态粒子在相同的相对湿度下潮解点不同,硝酸铵和硫酸铵是颗粒物中的主要吸湿成分.对不同天气条件下的气溶胶吸湿性分析,发现污染期间的吸湿增长因子(GF)和强吸湿组的数目比例(NFMH)都高于清洁期间,这与当时的气象条件以及粒子的内外部混合状态相关.观测还发现气溶胶粒子的吸湿性有明显的日变化特征,白天光照所引发的光化学反应以及混合层演变而造成粒子的吸湿性较强.机动车尾气排放的黑碳等不吸湿或弱吸湿颗粒物也会因为影响颗粒物的化学成分并进而对气溶胶吸湿性产生影响.     

广州气溶胶中有机物的分布及其与人体健康关系的研究

使用大流量采样器加分级采样头在广州市区和郊区设点进行了采样,用GC/ITD和GC/FID对大气气溶胶中的正构烷烃和多环芳烃做了定性和定量分析,并用回归法进行了数据处理,探求了气溶胶中有机物的含量与颗粒物粒径之间的分布关系。结果表明:34~46%的气溶胶颗粒物,31~49%的正构烷烃,50~70%的多环芳烃能穿透和滞留在肺泡;78~79%的气溶胶颗粒物,87~88%的正构烷烃,95~98%的多环芳烃能进入呼吸道,对人体健康的危害很大。研究还发现:大气颗粒物、正构烃和多环芳烃的粒径分布符合对数正态分布规律。      

Characteristics of mass distributions of aerosol particle and its inorganic water-soluble ions in summer over a suburb farmland in Beijing

Agricultural activity is one of the most important sources of aerosol particles. To understand the mass distribution and sources of aerosol particles and their inorganic water-soluble ions in a suburb farmland of Beijing, particle samples were collected using a microorifice uniform deposit impactor (MOUDI) in the summer of 2004 in a suburb vegetable field. The distribution of the particles and their inorganic water-soluble ions in the diameter range of 0.18–18 μm were measured. The dominant fine particle ions were SO₄ ²⁻, NO₃ ⁻, and NH₄ ⁺. The association of day-to-day variation of the concentration of these ions with temperature, humidity, and solar radiation suggested that they are formed by the reaction of NH₃ released from the vegetable field with the acid species produced from photochemical reactions. Fine particle K⁺ is likely from vegetation emission and biomass burning. Coarse particles like Ca²⁺, Mg²⁺, NO₃ ⁻, and SO₄ ²⁻ are suggested to come from the mechanical process by which the soil particle entered the atmosphere, and from the reaction of the acid species at the surface of the soil particle. The results show that fertilizer and soil are important factors determining the aerosol particle over agricultural fields, and vegetable fields in suburban Beijing contribute significantly to the aerosol particle. Translated from Environmental Science, 2006, 27(2): 193–199 [译自: 环境科学]     

南京冬季大气气溶胶粒子谱分布及其对能见度的影响

2009年11～12月采用宽范围气溶胶粒径谱仪（WPS）、自动气象站和能见度仪等高分辨率仪器对南京北郊气溶胶粒子的谱分布特征与气象因子的关系及其对大气能见度的影响进行研究.结果表明,数浓度谱呈双峰分布,主峰集中在0.04～0.1μm;质量浓度谱的2个主峰位于0.5～0.7μm和2.7μm左右;表面积谱的2个主峰分别位于...     

Size distribution of the secondary organic aerosol particles from the photooxidation of toluene

In a smog chamber, the photooxidation of toluene was initiated by hydroxyl radical （OH.） under different experimental conditions. The size distribution of secondary organic aerosol（SOA） particles from the above reaction was measured using aerodynamic particle sizer spectrometer. It was found from our experimental results that the number of SOA particles increased with increasing the concentration of toluene. As the reaction time prolonged, the sum of SOA particles was also increased. After a reaction time of 130 min, the concentration of secondary organic aerosol particles would be kept constant at 2300 particles/cm^3. Increasing illumination power of blacklamps could significantly induce a higher concentration of secondary organic aerosol particle. The density of SOA particles would also be increased with increasing concentration of CH30NO, however, it would be decreased as soon as the concentration of CH30NO was larger than 225.2 ppm. Nitrogen oxide with initial concentration higher than 30. 1 ppm was also found to have little effect on the formation of secondary organic aerosol.     

Size distribution and chemical composition of secondary organic aerosol formed from Cl-initiated oxidation of toluene

Secondary organic aerosol (SOA) formed from Cl-initiated oxidation of toluene was investigated in a home-made smog chamber. The size distribution and chemical composition of SOA particles were measured using aerodynamic particle sizer spectrometer and the aerosol laser time-of-flight mass spectrometer (ALTOFMS), respectively. According to a large number of single aerosol diameter and mass spectra, the size distribution and chemical composition of SOA were obtained statistically. Experimental results showed that SOA particles created by Cl-initiated oxidation of toluene is predominantly in the form of fine particles, which have diameters less than 2.5 m (i.e., PM2.5), and glyoxal, benzaldehyde, benzyl alcohol, benzoquinone, benzoic acid, benzyl hydroperoxide and benzyl methyl nitrate are the major products components in the SOA. The possible reaction mechanisms leading to these products are also proposed.     

在线单颗粒气溶胶质谱SPAMS对细颗粒物中主要组分提取方法的研究

在对美国气溶胶飞行时间质谱仪(aerosol time-of-flight mass spectrometer,ATOFMS)和中国单颗粒气溶胶质谱仪(single particle aerosol mass spectrometer,SPAMS)前期研究调研的基础上,总结并比较了国内外飞行时间质谱(time-of-flight mass spectrometry,TOF-MS)研究中含硫酸盐、硝酸盐、铵盐、有机碳(OC)和元素碳(EC)等5种主要组分颗粒的典型提取条件.结合SPAMS单颗粒谱图的特点,本研究通过限定示踪离子,对5种主要组分的提取方法进行改进,提出了新的SPAMS组分示踪离子提取方法.以北京市2013年1月SPAMS实测数据为例,对不同提取方法的结果进行对比分析.并将本研究方法 SPAMS主要组分结果与离线滤膜样品的实验数据进行对比,验证了本研究所提出的优化方案的合理性.同时指出SPAMS在未来的应用研究中需考虑的因素及进一步深入的研究方向.     

浙江金华秋季干气溶胶中主要化学组分的消光贡献解析

造成雾霾事件的主要原因是高浓度的大气细颗粒物污染.为了深入研究大气细颗粒物的消光来源,本研究采用高时间分辨率气溶胶观测仪器获得了浙江金华秋季PM1主要化学组分浓度及干气溶胶吸收系数和散射系数演变情况.结合有机气溶胶正矩阵因子解析模型(PMF)和多元线性回归方法,建立了拟合优度很高(R2=0.977)的细颗粒物中主要化学组分与干气溶胶消光系数间的定量关系模型.结果表明,观测期间消光贡献最大的是硫酸铵,贡献率为35.1%;其次是硝酸铵,贡献率为26.7%;二次有机气溶胶(SOA)、生物质燃烧有机气溶胶(BBOA)、黑碳(BC)及氯化铵的消光贡献率分别为14.3%、11.2%、8.7%、4.0%.在一些特定污染时段,BBOA具有最大的消光贡献,是导致此时大气能见度大幅度衰减的首要因子.     

鹤山气溶胶光学性质和单颗粒化学组分的研究

2014年10~11月在广东省鹤山大气超级站利用单颗粒气溶胶质谱仪（SPAMS）、积分式浊度仪和黑碳仪在线观测了单颗粒气溶胶的化学组成与气溶胶光学特征.采用Art-2a分类法将单颗粒分为9类：有机碳-硫酸盐/硝酸盐颗粒（OC-Sulfate/Nitrate）、元素碳-硫酸盐/硝酸盐颗粒（EC-Sulfate/Nitrate）、元素碳有机碳-硫酸盐/硝酸盐颗粒（ECOC-Sulfate/Nitrate）、高分子有机碳颗粒（HOC）、海盐颗粒（Sea-salt）、硅酸盐颗粒（Si-rich）、左旋葡聚糖颗粒（Lev）、钾-硫酸盐/硝酸盐颗粒（K-Sulfate/Nitrate）、金属颗粒（Metal）.从清洁期到灰霾期气溶胶的吸收系数、散射系数和单次散射反照率（SSA）显著升高,气溶胶消光能力增强,同时EC-Sulfate/Nitrate颗粒占比从34.8%降至31%,OC-Sulfate/Nitrate颗粒从9.9%增加至23.6%,K-Sulfate/Nitrate二次颗粒从8.5%增加至14%,且灰霾期OC-Sulfate/Nitrate颗粒与硫酸盐、硝酸盐和铵盐的混合程度增强,因此老化的OC-Sulfate/Nitrate颗粒和二次组分颗粒对气溶胶消光系数的增加有重要贡献.在大气相对湿度从50%增加到70%以上的过程中,气溶胶散射系数和吸收系数升高,消光系数由326.1Mm^-1增加到362.9Mm^-1,SSA有所下降,PM_2.5质量消光效率由4.98增加到5.99,EC-Sulfate/Nitrate颗粒和K-Sulfate/Nitrate二次颗粒占比下降,而OC-Sulfate/Nitrate颗粒的占比由7.79%增加到14.29%,且OC-Sulfate/Nitrate颗粒中富含硫酸盐、硝酸盐和铵盐,表明高相对湿度下老化的OC-Sulfate/Nitrate颗粒数目增多对气溶胶消光系数的增强有重要影响.     

Global analysis of aerosol particle characteristics

A technique is presented for global analysis of aerosol optical depth using satellite detected radiance from the NOAA AVHRR sensor. The technique also produces a measure of the slope of the aerosol size distribution from the spectral variation of scattered radiance. Global-scale summaries of aerosol optical depth and an aerosol particle size index are presented from April 1982 and 1983. The aerosol particle size index pattern from 1982 is compared to ship-measured oceanic dimethylsulfide (DMS) concentrations. Increases in the aerosol particle size index in the tropical Pacific Ocean are shown to be consistent with oceanic concentrations of DMS and subsequent particles formed by oxidation of DMS in the atmosphere.     

北京郊区农田夏季大气颗粒物质量和离子成分谱分布特征

农业活动是大气颗粒物的重要来源之一.为了研究北京郊区农田大气颗粒物质量和离子成分的分布,探讨其来源,本研究使用8级串联撞击式采样器MOUDI采集了2004年夏季北京远郊菜地的大气颗粒物样品,测量了0.18～18μm粒径段颗粒物质量和水溶性无机离子的粒径分布.细粒子的主要离子成分是SO₄^2-、NO₃^-和NH₄⁺,与温度、湿度和光照等条件相关,推测主要来自农田释放的NH₃与光化学生成的酸性物种的反应.细粒子中的K⁺可能来自植物的排放和生物质的燃烧.粗粒子中Ca²⁺、Mg²⁺、NO₃^-和SO₄^2-可能主要来自土壤颗粒物通过机械过程进入大气,以及其后酸性物种和土壤颗粒物表面的化学反应.研究结果表明,施用的化肥和土壤可能是决定农田大气中颗粒物的重要因素,北京远郊菜地对大气颗粒物可能有着重要的贡献.