Characterization of organic aerosols in Beijing using an aerodyne high-resolution aerosol mass spectrometer

Fine particle of organic aerosol(OA), mostly arising from pollution, are abundant in Beijing. To achieve a better understanding of the difference in OA in summer and autumn, a high-resolution time-of-flight aerosol mass spectrometer(HRTo F-AMS, Aerodyne Research Inc., USA) was deployed in urban Beijing in August and October 2012. The mean OA mass concentration in autumn was 30 ± 30 μg m-3, which was higher than in summer(13 ± 6.9 μg m-3). The elemental analysis found that OA was more aged in summer(oxygen-to-carbon(O/C) ratios were 0.41 and 0.32 for summer and autumn,respectively). Positive matrix factorization(PMF) analysis identified three and five components in summer and autumn, respectively. In summer, an oxygenated OA(OOA), a cooking-emission-related OA(COA), and a hydrocarbon-like OA(HOA)were indentified. Meanwhile, the OOA was separated into LV-OOA(low-volatility OOA) and SV-OOA(semi-volatile OOA);and in autumn, a nitrogen-containing OA(NOA) was also found. The SOA(secondary OA) was always the most important OA component, accounting for 55% of the OA in the two seasons. Back trajectory clustering analysis found that the origin of the air masses was more complex in summer. Southerly air masses in both seasons were associated with the highest OA loading, while northerly air masses were associated with the lowest OA loading. A preliminary study of OA components,especially the POA(primary OA), in different periods found that the HOA and COA all decreased during the National Day holiday period, and HOA decreased at weekends compared with weekdays.     

Determination of rate constants for reactions of some hydrohaloalkanes with OH radicals and their atmospheric lifetimes

Rate constants have been measured for the gas-phase reactions of hydroxyl radical with partly halogenated alkanes using the discharge-flow-EPR technique over the temperature range 298–460 K. The following Arrhenius expressions have been derived (units 10^–13 cm³ molecule^–1 s^–1): (8.1 _–1.2 ^+1.5 ) exp{–(1516±53)/T} for CHF₂Cl (HCFC-22); (10.3 _–1.5 ^+1.8 ) exp{–(1588±52)/T} for CH₂FCF₃ (HFC-134a); (11.3 _–1.6 ^+2.1 ) exp{–(918±52)/T} for CHCl₂CF₂Cl (HCFC-122); (9.2 _–2.0 ^+2.5 ) exp{–(1281±85)/T} for CHFClCF₂Cl (HCFC-123a).The atmospheric lifetimes for the substances have been estimated to be 12.6, 12.9, 1.05, and 4.8 years, respectively, and the accuracy of the estimates is discussed.     

Flow reactor and triple quadrupole mass spectrometer investigations of negative ion reactions involving nitric acid: Implications for atmospheric HNO3 detection by chemical ionization mass spectrometry

Atmospheric nitric acid measurements by ACIMS (Active Chemical Ionization Mass Spectrometry) are based on ion-molecule reactions of CO₃ ^-(H₂O) _n and NO₃ ^-(H₂O) _n with HNO₃. We have studied these reactions in the laboratory using a flow tube apparatus with mass spectrometric detection of reactant and product ions. Both product ion distributions and rate coefficients were measured. All reactions were investigated in an N₂-buffer (1–3 hPa) at room temperature. The reaction rate coefficients of OH^-, O₂ ^-, O₃ ^-, CO₄ ^-, CO₃ ^-, CO₃ ^-H₂O, NO₃ ^-, and NO₃ ^-H₂O were measured relative to the known rate k=3.0×10^-9 cm³ s^-1 for the reaction of O^- with HNO₃. The main product ion of the reaction of CO₃ ^-H₂O with HNO₃ was found to be (CO₃HNO₃)^- supporting a previous suggestion made on the basis of balloon-borne ACIMS measurements. For the reaction of bare CO₃ ^- with HNO₃ three product ions were observed, namely NO₃ ^-, (NO₃OH)^-, and (CO₃HNO₃)^-. The reaction rate coefficients for CO₃ ^-H₂O (1.7×10^-9 cm³ s^-1) and NO₃ ^-H₂O (1.6×10^-9 cm³ s^-1) were found to be close to the collision rate. The measured k values for bare CO₃ ^- (1.3×10^-9 cm³ s^-1) and NO₃ ^- (0.7×10^-9 cm³ s^-1) are somewhat smaller. The collisional dissociations of CO₃ ^-(H₂O) _n , NO₃ ^-(H₂O) _n (n=1, 2), (CO₃HNO₃)^- and (NO₃HNO₃)^-, occasionally influencing ACIMS measurements, were also studied. Fragment ion distributions were measured using a triple quadrupole mass spectrometer. The results showed that previous stratospheric nitric acid measurements were unimpaired from collisional dissociation processes whereas these processes played a major role during previous tropospheric measurements leading to an underestimation of nitric acid concentrations. Previous ACIMS HNO₃ detection was also affected by the conversion of CO₃ ^-(H₂O) _n to NO₃ ^-(H₂O) _n due to ion source-produced neutral radicals. A novel ACIMS ion source was developed in order to avoid these problems and to improve the ACIMS method.     

Oxidation of sulphur compounds in the atmosphere: I. Rate constants of OH radical reactions with sulphur dioxide,hydrogen sulphide,aliphatic thiols and thiophenol

The reactions of OH radicals with SO₂, H₂S, thiophenol, and a series of aliphatic thiols (1–5 C-atoms) have been investigated in 201 and 381 reaction chambers at 1 atm total pressure and 300 K using a competitive kinetic technique. Initially, OH radicals were produced by photolysis of CH₃ONO/NO mixtures in air. Applying this OH source rate constants for OH with SO₂, H₂S, and thiophenol in synthetic air were determined to be (1.1±0.2)×10^-12, (5.5±0.8)×10^-12 and (1.1±0.2)×10^-11 cm³ s^-1, respectively. However, when this method was applied to the aliphatic thiols the rate constants obtained were found to be dependent on the partial pressures of O₂ and NO. These effects have been attributed to the built-up of a radical species, not yet identified, which leads to uncontrolled chain reactions in the system. Using the photolysis of H₂O₂ at wavelengths greater than 260 nm as the OH source in 1 atm N₂, rate constants for the 1–5 aliphatic thiols in the range 2.9 to 5.6×10^-11 cm³ s^-1 were obtained. The rate constants obtained in the present study are compared with recent literature values.     

Seasonal variations of number size distributions and mass concentrations of atmospheric particles in Beijing

Particle number and mass concentrations were measured in Beijing during the winter and summer periods in 2003, together with some other parameters including black carbon (BC) and meteorological conditions. Particle mass concentrations exhibited low seasonality, and the ratio of PM2.5/PM10 in winter was higher than that in summer. Particle number size distribution (PSD) was characterized by four modes and exhibited low seasonality. BC was well correlated with the number and mass concentrations of accumulation and coarse particles, indicating these size particles are related to anthropogenic activities.Particle mass and number concentrations (except ultra-fine and nucleation particles) followed well the trends of 13C concentration for the majority of the day, indicating that most particles were associated with primary emissions. The diurnal number distributions of accumulation and coarse mode particles were characterized by two peaks.     

Size distributions of aerosol number concentrations and water-soluble constituents in Toyama, Japan: A comparison of the measurements during Asian dust period with non-dust period

Size-separated aerosol number concentrations and water-soluble constituents were measured in Toyama, the Hokuriku district, near the coast of the Japan Sea, during the spring and summer in 2003. The number concentrations of coarse particles were significantly high in April, which was due to Asian dust events called Kosa in Japanese. Particulate nssCa²⁺, which is mostly present in the coarse-mode particles, was significantly high in April. On the other hand, the concentrations of NH₄⁺ and nssSO₄²⁻, which mainly exist as the accumulation-mode particles were not high in April. The mass-size distributions of water-soluble constituents were compared with the size-separated number concentrations of particles. Backward trajectory analysis was also employed to examine the transport process of the air mass in Toyama.     

山东气溶胶光学厚度时空分布及其与地面大气污染物质量浓度的相关性分析

基于卫星的气溶胶光学厚度(aerosol optical thickness,AOT)是研究大气污染程度及时空变化的重要参考,由于大气污染物排放特征、地理和气候背景不同,不同区域AOT的时空分布及其与地面大气污染物质量浓度的相关性存在一定的差异。选取了2017年7月—2020年7月山东89个国家环境空气质量监测站数据、日本宇宙航空研究开发机构(Japan Aerospace Exploration Agency,JAXA)发布的葵花8号和9号气象卫星(Himawari-8／9)AOT产品、欧洲中期天气预报中心(European Center for Medium-Range Weather Forecasts,ECMWF)的ERA5再分析数据产品,研究了山东地区卫星AOT时空分布特征,AOT与地面污染物质量浓度的相关性,并得出了以下结论:1)山东存在两个主要的AOT低值区,分别位于鲁中山区一带,半岛丘陵并延伸到东部沿海一带,低值区的分布没有明显的季节变化;山东AOT年平均的高值区主要分布在山东西部、南部与外省接壤附近地区,以及渤海南部至莱州湾沿岸一带,在分析气溶胶跨省传输时值得关注。不同季节AOT的高值区分布存在差异。2)山东AOT白天变化呈现双峰结构,08时由峰值逐渐下降,11时转为上升,14时达全天最大值0.608;AOT的日变化趋势与细颗粒物(PM2.5)、O3等大气污染物质量浓度变化明显不同,是影响其相关性的重要因素。AOT月际变化中,存在两个显著的峰值6月(0.648)和10月(0.622),2月AOT最低。AOT的季节变化与地面污染物质量浓度的季节变化呈现一定的反位相特征。3)总体上AOT与PM2.5、O3等主要大气污染物质量浓度的相关性不高,一年之中,6月AOT与污染物的相关程度最低,1月的相关性最高;15—17时是AOT与污染物相关性最强的时间段,而10时相关性最差。单凭AOT难以定量反映污染物的分布特征,使用卫星开展地面大气污染监测分析还需纳入更多的因子进行分析。     

Gas phase measurements of hydrogen peroxide in Greenland and their meaning for the interpretation of H2O2 records in ice cores

The gas phase concentration of hydrogen peroxide at Summit, Central Greenland, has been measured continuously during June/July 1990 using a coil scrubber technique combined with liquid phase fluorometry. The concentrations ranged between 0.3 ppbv and 3.5 ppbv, which is considerably higher than expected from model calculations and can be explained by low deposition rates. The record shows pronounced diurnal variations with minimum concentrations during night and maximum concentrations in the afternoon. The nocturnal minima can be explained by scavenging of H₂O₂ by hoarfrost. The scavenging mechanisms of H₂O₂ by snow and the redistribution of H₂O₂ during firnification are discussed. There is indirect evidence, that H₂O₂ is uniformly distributed in the ice lattice and that the fractionation between H₂O₂ and H₂O is small during diffusional crystal growth from the vapor phase (co-condensation).     

江苏地区连续性雾霾天气的污染物浓度变化和特征分析

针对2013年1月江苏淮安地区发生的一次连续性雾霾天气过程,分析该天气过程中PM10和PM2.5的质量浓度演变特征、能见度与气象要素之间的关系、中低层环流特征以及污染物来源。结果表明:雾霾期间PM10和PM2.5质量浓度最低值出现在05:00至07:00(北京时间,下同)和13:00至17:00,最高值出现在21:00至23:00,PM10和PM2.5质量浓度并非同时达到极大值;持续变化较小的气压梯度、较低的风速、相对湿度的增大以及PM2.5和PM10质量浓度的增高是雾霾发生发展的必要条件;能见度与气压、相对湿度、PM2.5质量浓度的相关性较好,建立回归方程,对能见度的整体变化趋势拟合效果较好;高空环流形势平稳、中低层的暖平流、持续稳定少动的地面高压场分布为雾霾天气的持续发生发展提供了有利的形势背景;稳定的层结结构、中低层偏东及偏东北方向气团的输送、本地污染源以及严重的空气污染是此次过程中能见度偏低、霾天数较多的主要原因。     

Grab sampling for the determination of sulfur dioxide and dimethyl sulfide in air by isotope dilution gas chromatography/mass spectrometry

Developments allowing the direct determination of sulfur dioxide and dimethyl sulfide in grab samples by gas chromatography/mass spectrometry with isotopically labeled standards (GC/MS/ILS) are reported. Isotopomers of DMS and SO₂ are used as internal standards. Spiked air samples are dried to a dew point of <–60 °C and trapped cryogenically in loops of Teflon tubing. Sealed samples are transported to the laboratory under liquid nitrogen and later subjected to GC/MS analysis. Holding times of up to one month do not result in significant sample loss. For samples collected in a clean marine environment, concentrations of SO₂ and DMS greater than 5 and 8 pptv, respectively, are significantly different from blanks at the 95% confidence level. Average measurement precision derived from a propagation of errors are 9% for SO₂ and 42% for DMS at concentrations from 5–15 pptv.Improvements are outlined which should provide sensitivity and precision comparable to that of on-site GC/MS. The technique will allow increased flexibility for the determination of trace sulfur species in the field under conditions where deployment of a mass spectrometer is not possible.