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1.
The effect of temperature on the solubility of PAN and on its hydrolysis rate in near-neutral and slightly acidic water were studied in a bubble column apparatus. The results obtained are a Henry's law coefficient H=10–9.04±0.6 exp[(6513±376)/T] M atm–1, and a first-order hydrolysis rate constant k=106.60±1.0 exp[(–6612±662)/T] s-1, which was independent of pH in the range 3.2pH6.7. The products formed are nitrite and nitrate in approximately equal proportions under near-neutral conditions. At a pH<4, nitrite is oxidized in a secondary reaction, and nitrate becomes the only product at low pH. Previously measured deposition velocities of PAN on stagnant water surfaces are shown to be hydrolysis rate limited.  相似文献   

2.
In this paper we describe a gas-chromatographic method for PAN measurements in the background atmosphere, which has been adapted to the special requirements of aircraft based campaigns. The instrument is installed in a 1.21 m high, 19 inch rack which has a total weight of 70 kg and a power consumption of 750 VA. The gas chromatograph is equipped with a commercial liquid injector and a valve system for injection of gaseous samples. The gas-inlet system allows automatic injection of samples with defined and constant mass, independent from ambient pressure variations. Two different methods are used for calibration: Liquid PAN calibration samples and a diffusion source for gas-phase calibrations. Both methods have reproducibilities better than 90% and agree with each other to better than 85%. An optimum selectivity of the gas-chromatographic separation is obtained by a combination of two short megabore capillary columns of different polarity. The flow rates are 15 cm3/min, the column temperature is 26°C. For detection an electron-capture detector, operated at 30°C, is used. To allow a reliable control of these relatively low temperatures the instrument is equipped with peltier cooling. To avoid baseline or signal drifts caused by pressure variations in the aircraft cabin an electronic control of the system pressure is integrated into the instrument. The lower limit of detection is better than 15 ppt (3 ), the time needed for one measurement is less than 4 min. Preliminary results from a flight campaign conducted in June 1994 demonstrate the suitability of the instrument for airborne PAN measurements.  相似文献   

3.
During the POPCORN campaign between 3 and 24 August 1994 we measured peroxyacetyl nitrate (PAN) in a rural area of Mecklenburg-Vorpommern (North-Eastern Germany) above a corn field. A total of about 5000 PAN measurements were carried out within the three weeks of the campaign. Measured PAN mixing ratios ranged from below the detection limit of 10 ppt up to an afternoon maximum of 1 ppb. The mean value of all data was 140 ppt. The daily mean PAN mixing ratios were typically in the range of 50 to 250 ppt, but during a clean air episode PAN mixing ratios of well below 40 ppt were observed. The characteristic relative diurnal variation of the PAN mixing ratios with a late night/early morning minimum and an afternoon maximum persisted during these episodes. The daily averages of the PAN mixing ratios showed clear episodic variations which coincided with the duration of typical synoptic episodes of two to six days duration. Based on the measurements of the various parameters determining the PAN formation and destruction rates, the local budget for PAN was calculated. During daytime the calculated net photochemical formation rate of PAN was nearly always significantly higher than the observed change of the PAN concentration. This demonstrates that substantial amounts of PAN (often in the range of several hundred ppt/h) were exported from the corn field. The resulting removal of NOx to some extent effects the budget of nitrogen oxides (NOx), but the export of odd oxygen radicals in the form of PAN during daytime often amounted up to 30–50% of the OH-radical formation by ozone photolysis. Thus the importance of PAN as reservoir and transport medium for odd oxygen radicals can be very substantial and may have a significant impact on the budget and distribution of odd oxygen radicals.  相似文献   

4.
The effect of sunlight on air containing hydrocarbons and nitrogen oxides leads to a very complex series of reactions which form, among other secondary pollutants, peroxyacetylnitrate (PAN). This compound is believed to be the most useful indicator of photochemical pollution, and has been monitored for several months at the University of Creteil (Paris, France). Although it is commonly accepted that high PAN levels occur more frequently in summer, our results show elevated PAN concentrations during nonsummer periods, precisely during two episodes in October 1985 and February 1986. A close examination of these episodes indicates that, in addition to local photochemical production, long-range transport of polluted air masses can occur in winter, revealing the influence of emissions from central Europe.  相似文献   

5.
过氧乙酰硝酸酯（PAN）是由VOCs和NOx的光化学反应生成的一种典型二次污染物,比O3更适合作为光化学污染的指示剂.2019年6—10月对浙江中部盆地金华市大气中PAN进行了在线监测,并对影响其体积分数变化的因素进行了分析,同时还分析了一次典型的光化学污染过程.结果表明,观测期间PAN的平均体积分数为0.656×10-9,最高体积分数为4.348×10-9,日均体积分数水平在0.130×10-9~2.203×10-9之间.PAN日变化特征显著,9月为明显的双峰变化,其他月份均为单峰.受气象条件的影响,夏季的污染程度显著低于秋季.9月27—30日典型污染时段内,PAN的小时均值是整个观测期均值的2.8倍,污染以本地积累为主.前体物浓度水平差异与去除机制的不同是影响PAN和O3相关性的重要因素,此外NO/NO2的比值是影响PAN生成速率的重要因素,PAN的峰值基本出现在NO/NO2比值较低的时段.在生成PAN的VOCs物种中,丙烷、乙烷和间/对二甲苯所占比例较大.  相似文献   

6.
Springtime measurements of NOx, ozone, PAN,J(NO2), and other compounds were made near Ny-Ålesund,Svalbard (78°54N, 11°53E), in 1994 and Poker Flat,Alaska (65°08N, 147°29W), in 1995. At Svalbard medianmixing ratios for PAN and NOx of 237 and 23.7 pptv,respectively, were observed. The median mixing ratios at Poker Flat for PANand NOx were 79.5 and 85.9 pptv, respectively. These data areused to estimate thermal PAN decomposition using several differentapproaches. At Svalbard PAN decomposition was very small, while at PokerFlat up to 30 pptv/h PAN decomposed. At both sites the NOx/PANratio increased with temperature between –10 and 20°C implyingthat PAN decomposition is an important NOx source. In-situozone production was calculated from the measured NO, NO2,O3, J(NO2), and temperature data, using thesteady state assumption Median ozone production was 605 pptv/h at PokerFlat, and one order of magnitude smaller at Svalbard during the daytime.Only at Poker Flat could a direct influence on the diurnal ozone cycle beobserved from in-situ production. These results imply that PAN decompositionis a major source of NOx in the high latitude troposphere, andthat this contributes to the observed spring maximum in surface ozone.  相似文献   

7.
A model with spectral microphysics was developed to describe the scavenging of nitrate aerosol particles and HNO3 gas. This model was incorporated into the dynamic framework of an entraining air parcel model with which we computed the uptake of nitrate by cloud drops whose size distribution changes with time because of condensation, collision-coalescence and break-up. Significant differences were found between the scavenging behavior of nitrate and our former results on the scavenging behavior of sulfate. These reflect the following chemical and microphysical differences between the two systems:
  1. nitrate particles occur in a larger size range than sulfate particles.
  2. HNO3 has a much greater solubility than SO2 and is taken up irreversibly inside the drops in contrast to SO2.
  3. nitric acid in the cloud water is formed directly on uptake of HNO3 gas whereas on uptake of SO2 sulfuric acid is formed only after the reaction with oxidizing agents such as e.g., H2O2 or O3.
  4. nitrate resulting from uptake of HNO3 is confined mainly to small drops, whereas sulfate resulting from uptake of SO2 is most concentrated in the largest, oldest drops, which have had the greatest time for reaction.
Sensitivity studies showed that the nitrate concentration of small drops is significantly affected by the mass accommodation coefficient.  相似文献   

8.
Simultaneous measurements of peroxy and nitrate radicals at Schauinsland   总被引：3，自引：0，他引：3  
We present simultaneous field measurements of NO3 and peroxy radicals made at night in a forested area (Schauinsland, Black Forest, 48° N, 8° N, 1150 ASL), together with measurements of CO, O3, NO x , NO y , and hydrocarbons, as well as meteorological parameters. NO2, NO3, HO2, and (RO2) radicals are detected with matrix isolation/electron spin resonance (MIESR). NO3 and HO2 were found to be present in the range of 0–10 ppt, whilst organic peroxy radicals reached concentrations of 40 ppt. NO3, RO2, and HO2 exhibited strong variations, in contrast to the almost constant values of the longer lived trace gases. The data suggest anticorrelation between NO3 and RO2 radical concentrations at night.The measured trace gas set allows the calculation of NO3 and peroxy radical concentrations, using a chemical box model. From these simulations, it is concluded that the observed anthropogenic hydrocarbons are not sufficient to explain the observed RO2 concentrations. The chemical budget of both NO3 and RO2 radicals can be understood if emissions of monoterpenes are included. The measured HO2 can only be explained by the model, when NO concentrations at night of around 5 ppt are assumed to be present. The presence of HO2 radicals implies the presence of hydroxyl radicals at night in concentrations of up to 105 cm–3.  相似文献   

9.
Products and mechanisms for the gas-phase reactions of NO3 radicals with CH2=CHCl, CH2=CCl2, CHCl=CCl2,cis-CHCl=CHCl andtrans-CHCl=CHCl in air have been studied. The experiments were carried out at 295±2 K and 740±5 Torr in a 480-L Teflon-coated reaction chamber and at 295±2 K and 760±5 Torr in a 250-L stainless steel reactor. NO3 was generated by the thermal dissociation of N2O5. Experiments with15NO3 and CD2CDCl have also been performed. The initially formed nitrate peroxynitrates decay into carbonyl compounds, nitrates, HCl and ClNO2. In adidtion, there are indications of nitrooxy acid chlorides being produced. The reactions with CH2=CCl2 and CHCl=CCl2 are more complex due to release of chlorine atoms which eventually lead to formation of chloroacid chlorides.A general reaction mechanism is proposed and the observed concentration-time profiles of reactants and products are simulated for each compound. The rate constants for the initial step of NO3 addition to the chloroethenes are determined as: (2.6±0.5, 9.4±0.9, 2.0±0.4 and 1.4±0.4) × 10–16 cm3 molecule–1 s–1 for CH2=CHCl, CH2=CCl2, CHCl=CCl2 andcis-CHCl=CHCl, respectively.  相似文献   

10.
During the BERLIOZ field phase on 20 July 1998 a 40 km wide ozone-plume 30 to 70 km north of Berlin in the lee of the city was detected. The ozone mixing ratio inside the plume was app. 15 ppb higher than outside, mainly caused by high ozone precursor emissions in Berlin, resulting in a net chemical ozone production of 6.5 ppb h–1, which overcompensates ozone advection of –3.6 ppb h–1 andturbulent diffusion of –1.1 ppb h–1. That means, although moreozone leaves the control volume far in the lee of Berlin than enters it at the leeside cityborder and although turbulent diffusion causes a loss of ozone in the leeside control volume the chemical production inside the volume leads to a net ozone increase. Using a semi-Lagrangian mass budget method to estimate the net ozone production, 5.0 ppb h–1 are calculated for theplume. This means a fraction of about 20% of ozone in the plume is producedby local emissions, therefore called `home made' by the Berlin emissions. For the same area KAMM/DRAIS simulations using an observation based initialisation, results in a net production rate between 4.0 and 6.5 ppbh–1, while the threefold nested EURAD model gives 6.0 ppbh–1. The process analysis indicates in many cases goodagreement (10% or better) between measurements and simulations not only in the ozone concentrations but also with respect to the physical and chemical processes governing the total change. Remaining differences are caused by different resolution in time and space of the models and measurements as well as by errors in the emission calculation.The upwind-downwind differences in PAN concentrations are partly similar to those of ozone, because in the BERLIOZ case they are governed mainly by photochemical production. While in the stable boundary layer at night and windward of Berlin 0.1 to 0.3 ppb are detected, in the centre of the plume at noon concentrations between 0.75 ppb and 1.0 ppb are measured. The O3/PAN ratio is about 80 to 120 and thus due to the relatively lowPAN concentrations significantly higher than found in previous studies. The low PAN formation on 20 July, was mainly restricted by the moderate nonmethane hydrocarbon levels, whereas high PAN concentrations of 3.0 ppb on 21 July, are caused by local production in the boundary layer and by large scale advection aloft.  相似文献   

11.
Two procedures for the calibration of an electron capture detector (ECD) for peroxyacetyl nitrate (PAN) are discussed. One is based on the first-order decay rate of the the PAN mixing ratio in conditioned glass storage vessels. The other method makes use of the photochemical generation of PAN in mixtures of acetone and NO2 in air. For this purpose a Penray Hg lamp was inserted into a glass vessel filled with 1 atmosphere of air containing 10 ppm NO2 and 1% acetone. After 3 min of irradiation, the average PAN mixing ratio formed was 8.87±0.25 ppmv as determined in six separate runs.  相似文献   

12.
Free tropospheric measurements of ozone, peroxyacetylnitrate andprecursors (CO, NMHC) that were made within the framework of the EUROTRACsub-project TOR (Tropospheric Ozone Research) between 1990 and 1995 at theGAW station Izana, Tenerife (28°18N, 16°30W) arediscussed. The average annual cycles reveal the importance of transport fromnorthern mid-latitudes and the role of photo-chemistry. According toair-mass trajectories, which were supplied to us from AEROCE(Atmosphere/Ocean Chemistry Experiment), transport from northernmid-latitudes is associated with high precursor concentrations in winter,whereas ozone concentrations in winter are not much influenced by transportpatterns, suggesting a rather uniform distribution over the northern part ofthe Northern Hemisphere around mean value of 43 ± 5 ppb. In summer,high ozone concentrations of up to 90 ppb are often encountered duringtransport from north, while the levels of precursors are much lower than inwinter, because of photochemical destruction. Trajectories from southerlylatitudes and the Sahara usually have the lowest ozone concentrationsassociated with them.  相似文献   

13.
大气中硝酸盐、硫酸盐、铵和钙的浓度   总被引：2，自引：0，他引：2  
1985年10月,在中国的三个不同地点用太氟龙和尼龙滤膜采样系统观测了硝酸根、硫酸根、铵和钙的浓度。平均而言,硫酸根的摩尔浓度与硝酸根的摩尔浓度之比不到2。考虑到中国燃煤大量排放SO_2这一事实,这一低比值有点出乎预料。在北京钙是最重要的阳离子,而在华北山区的兴隆天文观测站和南方城市长沙气溶胶中铵离子多于钙离子。在北风条件下,兴隆的硫酸根和硝酸根浓度与文献中报道的欧洲和北美的本底值接近。因此,兴隆天文观测站是研究亚洲大陆本底空气的理想地点。  相似文献   

14.
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15.
The present study was carried out between October 2003 and September 2004 at an urban background station near the Mediterranean coast in southeastern Spain. The sulfate and nitrate content was determined in 332 PM10 and PM2.5 daily samples. The results show that the seasonal variation of nitrate measured in PM10 does not correspond with what has been observed at other locations in the Iberian Peninsula, where the minima are reached during the summer months due to decomposition of ammonium nitrate at high temperatures. The recorded levels of PM10 nitrate were slightly higher in summer due to an increase in the concentrations of coarse mode nitrate. On the contrary, both the concentrations and the percentages of nitrate in PM2.5 were lowest from June to September. The sulfate levels in both PM10 and PM2.5 were maxima in summer because the oxidation rate of SO2 increases with solar radiation. An elevated correlation (0.72 < r < 0.92) between the monthly average concentrations and percentages of sulfate and solar radiation has been found. We have also investigated the influence that Saharan dust intrusions and high pollution episodes have upon the sulfate and nitrate concentrations. Both types of events increased NO3− and SO42− levels, particularly the high pollution episodes.  相似文献   

16.
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17.
在过去的20多年里,中外对硫酸盐气溶胶做了大量的研究,对它在大气中的排放、含量、光学特征和辐射强迫有了深入的认识;由于硝酸盐气溶胶在大气中平均含量比硫酸盐低很多,因此过去人们对硝酸盐的研究没有给予重视。然而,近年来的研究表明,硝酸盐气溶胶的散射性质在某些波段甚至强于硫酸盐;同时,由于未来对人为硫酸盐前体物的减排,硫酸盐气溶胶排放会大幅度减少,而硝酸盐气溶胶的排放却增长迅速,其在人为气溶胶中所占的比重越来越高,将会导致其在未来造成的辐射强迫有可能超过硫酸盐,使得其在地区范围内和季节尺度上成为重要的辐射强迫和气候影响因子。中国是硝酸盐气溶胶排放量较大的地区,硝酸盐对未来中国气候和气候变化的影响显得越来越重要。因此,就近年来有关硝酸盐气溶胶的排放和在大气中的浓度变化、光学厚度分布特征及其辐射强迫的研究进展做了回顾和介绍,并对其未来的研究做了展望。  相似文献   

18.
Peroxyacetyl nitrate (PAN,CH3C(O)O2NO2) has been measured inthe polluted boundary layer and free troposphere by thermal conversion tonitrogen dioxide (NO2) followed by detection of thedecomposition product with a Scintrex LMA-3 NO2-luminolinstrument. Following laboratory tests of the efficiency of PAN conversionand investigations of possible interferences, the technique was evaluated atthe West Beckham TOR (Tropospheric Ozone Research) Station near the northNorfolk coast in Eastern England between September 1989 and August 1990. PANmeasured by the new technique was reasonably well correlated with PANrecorded using electron capture gas chromatography (EC/GC). PAN was alsowell correlated with ozone (O3) in the summer months. Springand autumn episodes of simultaneously high concentrations of PAN andO3 were examined in conjunction with air parcelback-trajectories and synoptic- and local-scale meteorology in a study ofthe sources of photooxidants on the east coast of England. Spring-timemeasurements of PAN made in the free troposphere in a light aircraft ataltitudes up to 3.1 km showed the presence of 0.54 and 0.26 ppbv PAN inpolar maritime and mid-latitude oceanic air masses, respectively. Thetechnique is particularly suited to airborne applications because potentialinterferences are minimised and the frequency of measurements is higher thangenerally achieved with EC/GC methods.  相似文献   

19.
2007年6—8月T213与ECMWF及日本模式中期预报性能检验   总被引：1，自引：3，他引：1  
李勇 《气象》2007,33(11):93-100
对2007年6—8月T213模式进行天气学检验,并与欧洲中心ECMWF模式及日本模式进行了比较。结果表明:3种模式对亚洲中高纬环流形势的调整演变具有较好的预报性能。综合来看,ECMWF模式对各系统及要素的预报误差最小,最接近实况,日本模式和T213模式稍差,稳定性不如ECMWF模式,特别是T213模式对0709号台风圣帕路径及强度的预报与实况相差较大,而ECMWF模式及日本模式预报较为准确。  相似文献   

20.
Results from numerical investigations regarding the exchange of HNO3, NH3, and NH4NO3 between the atmosphere and the biosphere are presented. The investigations were performed with a modified inferential method which is based on the generally accepted micrometeorological ideas of the transfer of momentum, sensible heat and matter near the Earth's surface and the chemical reactions among these nitrogen compounds. This modified inferential method calculates the micrometeorological quantities (such as the friction velocity and the fluxes of sensible and latent heat), the height-invariant fluxes of the composed chemically conservative trace species with group concentrationsc 1=[HNO3]+[NH4NO3] (total nitrate),c 2=[NH3]+[NH4NO3] (total ammonia), andc 3=[HNO3]-[NH3] as well as the fluxes of the individual nitrogen compounds. The parameterization of the fluxes is based on the flux-gradient relationships in the turbulent region of the atmospheric surface layer. The modified inferential method requires only the data of wind velocity, temperature, humidity and concentrations (HNO3, NH3, and NH4NO3) measured at a reference height by stations of a monitoring network.  相似文献   

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