Rate constant measurement for the reactions of OH and Cl with peroxyacetyl nitrate at 298 K

The gas phase reactions of peroxyacetyl nitrate (PAN) with OH and Cl have been studied using the discharge-flow EPR method. The rate constants are found to be k ₃=(7.5±1.4)×10^-14 and k ₄=(3.7±1.7)×10^-13 cm³ molecule^-1 s^-1 at 298 K, respectively. These results confirm that the OH+PAN reaction will be the dominant sink of PAN in the middle and upper troposphere, whereas the reaction Cl+PAN will be negligible in contrast with previous estimations.     

Estimation of aerosol deposition rate from the data of geochemical studies and atmospheric radioactive pollution monitoring

The aerosol deposition rate is computed for some chemical elements from the resuits of studies on the elemental composition of atmospheric aerosol and snow cover in the background and anthropogenic areas in the Primorskii krai as well as for the radionuclide ¹³⁷Cs and suspended matter from the data of atmospheric radioactive pollution monitoring. Taking into account the differences in sampling methods, the rather close values of deposition rate were obtained for chemical elements and radionuclide.     

Laser desorption/ionization mass spectrometric study of secondary organic aerosol formed from the photooxidation of aromatics

Five aromatic hydrocarbons – benzene, toluene, ethylbenzene, p-xylene and 1,2,4-trimethylbenzene – were selected to investigate the laser desorption/ionization mass spectra of secondary organic aerosols (SOA) resulting from OH-initiated photooxidation of aromatic compounds. The experiments were conducted by irradiating aromatic hydrocarbon/CH₃ONO/NO _X mixtures in a home-made smog chamber. The aerosol time-of-flight mass spectrometer (ATOFMS) was used to measure the aerodynamic size and chemical composition of individual secondary organic aerosol particles in real-time. Experimental results showed that aerosol created by aromatics photooxidation is predominantly in the form of fine particles, which have diameters less than 2.5 μm (i.e. PM2.5), and different aromatic hydrocarbons SOA mass spectra have eight same positive laser desorption/ionization mass spectra peaks: m/z = 18, 29, 43, 44, 46, 57, 67, 77. These mass spectra peaks may come from the fragment ions of the SOA products: oxo-carboxylic acids, aldehydes and ketones, nitrogenated organic compounds, furanoid and aromatic compounds. The possible reaction mechanisms leading to these products were also discussed.     

A discharge flow mass-spectrometric study of the reaction between the NO3 radical and isoprene

The kinetics and mechanism of the reactionNO₃+CH₂=C(CH₃)–CH=CH₂productswere studied in two laboratories at 298 K in the pressure range 0.7–3 torr using the discharge-flow mass-spectrometric method. The rate constant obtained under pseudo-first-order conditions with excess of either NO₃ or isoprene was: k ₁=(7.8±0.6)×10^–13 cm³ molecule^–1 s^–1. The product analysis indicated that the primary addition of NO₃ occurred on both -bonds of the isprene molecule.     

中国南方地基雨量计观测与星载测雨雷达探测降水的比较分析

利用热带测雨卫星(TRMM)上搭载的测雨雷达(PR)探测结果和中国40°N以南地区约430个台站雨量计观测结果,分析研究了1998-2005年中国南方地区这两种降水资料气候分布的异同.研究结果表明两种降水资料在2.5°空间水平分辨率上,所描述的中国南方降水率气候分布在多年年平均和季平均上具有较好的一致性,但在降水率极值和极值区范围大小等细节上两者还存在一定的差异,主要是地面雨量计结果相对PR结果偏高,其中中同南方50%以上地区两者相差在1 mm/d以内、30%的地区两者相差在1-2 mm/d,夏季差异可超过2 mm/d.对两种降水资料差异的原因分析表明,地面雨量计空间分布密度是影响两者差异的决定性因素,当格子内雨量计超过6个时,两者的相关系数大于0.7;夏季两种降水资料的相关性都比其他季节差,不论格子内的雨量计数量多与少;对流降水多发地区,两种降水资料之间的差异大于层云降水多发地.利用PR探测结果对夏季青藏高原多年月平均降水率分布及高原东、西部的降水特点的分析表明,6月高原东部出现2 mm/d左右的降水区,而在7和8月1 mm/d的降水区域基本覆盖了除高原西部以外的整个高原,其中高原中部地区出现降水率近3mm/d的大值区.月降水距平的时间演变表明,高原降水偏少月份要多于偏多月份.     

Further studies of the temperature dependence of the rate coefficients for the reactions of OH with a series of ethers under simulated atmospheric conditions

The following temperature-dependent rate coefficients (k/cm³ molecule^–1 s^–1) of the reactions of hydroxyl radicals with aliphatic ethers have been determined over the temperature range 247–373 K by a competitive flow technique: diethyl ether,k _OH=5.2×10^–12 exp[(262±150)/T]; methyln-butyl ether,k _OH=5.4×10^–12 exp[(309±150)/T]; ethyln-butyl ether,k _OH=7.3×10^–12 exp[(335±150)/T]; di-n-butyl ether,k _OH=5.5×10^–12 exp[(502±150)/T] and di-n-pentyl ether,k _OH=8.5×10^–12 exp[(417±150)/T]. The data have been measured relative to the rate coefficientk(OH + 2,3-dimethylbutane)=6.2×10^–12 cm³ molecule^–1 s^–1 independent of temperature.Previous discrepancies in the room-temperature rate coefficients for the OH reactions with ethyln-butyl ether and di-n-butyl ether, obtained in the flow and static experiments of Bennett and Kerr (J. Atmos. Chem. 8, 87–94, 1989;10, 29–38, 1990) compared with those of Wallingtonet al. (Int. J. Chem. Kinet. 20, 541–547, 1988;21, 993–1001, 1989) and of Nelsonet al. (Int. J. Chem. Kinet. 22, 1111–1126, 1990) have been resolved. The results are considered in relation to the available literature data and evaluated rate expressions are deduced where possible. The data are also discussed in terms of structure-activity relationships.     

Observation of DMSO and CH3S(O)OH from the gas phase reaction between DMS and OH

Products and mechanisms have been investigated for the reactions between dimethylsulfide (DMS) and dimethylsulfoxide (DMSO) and the hydroxyl radical (OH) in the presence of NO_x. All of the experiments were performed in a 480 L reaction chamber, applying Fourier transform infrared spectroscopy (FT-IR) and ion chromatography as the analytical techniques.In addition to the sulfur containing products that are known to be produced from the gas phase reaction between DMS and OH (SO₂, dimethylsulfone, methylsulfonyl peroxynitrate, methanesulfonic acid, H₂SO₄), DMSO and methanesulfinic acid (CH₃S(O)OH) were also observed as products. Only SO₂, DMSO₂ and methylsulfonyl peroxynitrate were found as sulfur containing products in the reaction between DMSO and OH. Based on these new results we propose a mechanism for the atmospheric oxidation of DMS and DMSO by OH radical.     

Kinetics of the reactions of hydroxyl radicals with aliphatic ethers studied under simulated atmospheric conditions: Temperature dependences of the rate coefficients

Rate coefficients have been measured for the reactions of hydroxyl radicals with five aliphatic ethers over the temperature range 242–328 K. Competitive studies were carried out in an atmospheric flow reactor in which the hydroxyl radicals were generated by the photolysis of methyl nitrite in the presence of air containing nitric oxide. The reaction of OH with 2,3-dimethyl-butane was used as the reference reaction and the following Arrhenius parameters have been obtained for the reactions: OH+RORproducts:

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.     

2015—2019年太行山南麓O3浓度特征及其与气象因子的关系

利用2015—2019年太行山南麓(即山西省晋城市)O3浓度和中国太阳总辐射资料,分析了该地区O3浓度的时空变化特征,及其与风、相对湿度、降水、雾霾、气温、太阳总辐射等气象因子的关系.结果表明:O3浓度呈逐年增加趋势,夏季浓度明显高于冬季,月变化为单峰型,峰值出现在6月,谷值出现在1月,日变化白天高于夜间;O3浓度的空...     

The equilibrium constant of NO2 with N2O4 and the temperature dependence of the visible spectrum of NO2: A critical review and the implications for measurements of NO2 in the polar stratosphere

Measurements of stratospheric NO₂ by ground-based visible spectrometers rely on laboratory measurements of absorption cross-sections. We review low-temperature laboratory measurements, which disagree by amounts claimed to be significant. Our recalculation of their errors shows that in general disagreements are not significant and that errors in the ratios of cross-sections at low to room temperature are between ±3% and ±8.8%. Of these errors, up to ±3.5% was contributed by errors in the equilibrium constant,K _p, in those measurements where the pressure was above 0.1 mbar.We review measurements and calculations ofK _p, which were accurate to ±5% from 300 to 233 K. Each method was potentially flawed. For example, infrared measurements of the partial pressure of NO₂ ignored the dependence of absorption on total pressure. From thermodynamic theory, formulae forK _pcan be derived from expressions for the variation of heat capacity with temperature. Contrary to common belief, coefficients in the formulae used by spectroscopists were not derived from the thermodynamic quantities. Rather, they were fitted to measurements or to calculations. Hence, they are empirical and it is dangerous to extrapolate below 233 K, the lowest temperature of the measurements.There are no measurements of NO₂ cross-sections below 230 K. Extrapolation of these cross-sections to analysis of measurements of NO₂ at the low temperatures of the Arctic and Antarctic stratosphere is also dangerous. For satisfactory analysis of polar spectra, the NO₂ cross-sections should be measured at temperatures down to 190 K with a relative accuracy of ±1%. This difficult experiment would need a cell of minimum length 32 m whose length can be adjusted. Because their effects are circular, many errors cannot be removed simply. Although circular errors also arise in the measurements ofK _pand of the infrared spectrum, their weights differ from those in the visible spectrum. The optimum experiment might therefore simultaneously measure the visible and infrared spectra andK _p.