Validation of Ground-Based Visible Measurements of Total Ozone by Comparison with Dobson and Brewer Spectrophotometers

Comparisons of total column ozone measurements from Dobson, Brewer and SAOZ instruments are presented for the period 1990 to 1995 at seven stations covering the mid- and the high northern latitudes, as well as the Antarctic region. The main purpose of these comparisons is to assess, by reference to the well established Dobson network, the accuracy of the zenith-sky visible spectroscopy for the measurement of total ozone. The strengths and present limitations of this latter technique are investigated. As a general result, the different instruments are found to agree within a few percent at all stations, the best agreement being obtained at mid-latitudes. On average, for the mid-latitudes, SAOZ O₃ measurements are approximately 2% higher than Dobson ones, with a scatter of about 5%. At higher latitudes, both scatter and systematic deviation tend to increase. In all cases, the relative differences between SAOZ and Dobson or Brewer column ozone are characterised by a significant seasonal signal, the amplitude of which increases from about 2.5% at mid-latitude to a maximum of 7.5% at Faraday, Antarctica. Although it introduces a significant contribution to the seasonality at high latitude, the temperature sensitivity of the O₃ absorption coefficients of the Dobson and Brewer instruments is shown to be too small to account for the observed SAOZ/Dobson differences. Except for Faraday, these differences can however be largely reduced if SAOZ AMFs are calculated with realistic climatological profiles of ozone, pressure and temperature. Other sources of uncertainties that might affect the comparison are investigated. Evidence is found that the differences in the air masses sampled by the SAOZ and the other instruments contribute significantly to the scatter, and the impact of the tropospheric clouds on SAOZ measurements is displayed.     

Meteorological Aspects, Ozone, and Solar Radiation Measurements During POPCORN 1994

Meteorological data, ozone mixing ratios, and photolysis frequencies for the period August 2 to August 24, 1994, are presented and discussed in support of the field campaign POPCORN (Photochemistry of Plant Emitted Compounds and OH Radicals in Northeastern Germany). Measurements of temperature, ozone, and wind speed at different heights are used to evaluate micro-meteorological parameters. The observations provide information about local influences on the air mass composition. The analysis of radio sonde data of nearby stations provides the height of the planetary boundary layer.     

CALCULATION OF AIR-MASS FACTORS FOR O_3

In conversion of the integrated slant column amount of atmospheric ozone(O_3)measured bythe ground-based spectrometer technique during twilight to the vertical quantity,the air-massfactor(AMF)is an important parameter.In this work,calculations of AMF for ozone wereperformed for different atmospheres.It is shown that the O_3 AMF has seasonal variations with theminimum at the beginning of spring and the maximum in summer due to the seasonal change in thevertical distributions of O_3.A parameterization relation is obtained between O_3 AMF and opticalthickness of stratospheric volcanic aerosols based on the Monte-Carlo radiative transfersimulations.     

EFFECTS OF SOLAR FLARE ON THE MIDDLE ATMOSPHERE

The SME satellite data of solar UV radiation and mesospheric ozone during solar flare in 1982are analyzed.The results show that the Ha line index used in the solar flare classification is not aproper parameter for studying the effects of solar activity on the photochemical process in themiddle atmosphere.     

EFFECTS OF SOLAR FLARE ON THE MIDDLE ATMOSPHERE*

The SME satellite data of solar UV radiation and mesospheric ozone during solar flare in 1982 are analyzed.The results show that the Ha line index used in the solar flare classification is not a proper parameter for studying the effects of solar activity on the photochemical process in the middle atmosphere.     

东亚地区夏季风活动与对流层顶臭氧含量变化的关系探讨

利用1976～2001年东亚地区的风场、气压场和对流层顶臭氧浓度观测资料,选取并计算了3种当前使用较为广泛的东亚季风指数,分析了夏季期间上述指数与对流层顶臭氧的相关,从而对东亚地区季风活动与对流层顶臭氧含量分布的关系进行了探讨.分析表明:(1)东亚SMI夏季风指数的强弱与西太平洋副热带高压区的对流层顶臭氧之间存在着正相关,且相关性较好;(2)指数EAMI与对流层顶臭氧存在相关,具体表现为在南海热带季风区存在着负相关、在大陆--日本副热带季风区存在正相关、西太平洋副热带高压区存在较好的正相关;(3)而在副热带梅雨锋区,EASMI指数的强弱与对流层顶臭氧含量变化存在较好的正相关,在热带季风槽区,EASMI指数的强弱与对流层顶臭氧含量变化存在较好的负相关.     

The annual cycle of peroxides and ozone in marine air at Cape Grim, Tasmania

The concentration of gas-phase peroxides has been measured almost continuously at the Cape Grim baseline station (41° S) over a period of 393 days (7702 h of on-line measurements) between February 1991 and March 1992. In unpolluted marine air a distinct seasonal cycle in concentration was evident, from a monthly mean value of>1.4 ppbv in summer (December) to <0.2 ppbv in winter (July). In the summer months a distinct diurnal cycle in peroxides was also observed in clean marine air, with a daytime build-up in concentration and decay overnight. Both the seasonal and diurnal cycles of peroxides concentration were anticorrelated with ozone concentration, and were largely explicable using a simple photochemical box model of the marine boundary layer in which the central processes were daytime photolytic destruction of ozone, transfer of reactive oxygen into the peroxides under the low-NO_x ambient conditions that favour self-reaction between peroxy radicals, and continuous heterogeneous removal of peroxides at the ocean surface. Additional factors affecting peroxides concentrations at intermediate timescales (days to a week) were a dependence on air mass origin, with air masses arriving at Cape Grim from higher latitudes having lower peroxides concentrations, a dependence on local wind speed, with higher peroxides concentrations at lower wind speeds, and a systematic decrease in peroxides concentration during periods of rainfall. Possible physical mechanisms for these synoptic scale dependencies are discussed.     

Boundary-Layer Ozone in Croatia

An analysis of ozone distribution in the atmosphericboundary layer based on monitoring data from two TORstations in Croatia is given. The levels were found tobe generally higher than expected for the continentalbackground. At the Puntijarka station, which can betaken as representative for the region, high valuesare mainly associated with transport from the west.The RBI station represents an urban site withoccasional photosmog situations. Short termmeasurements along the Adriatic coast have shown thatthere is a negative north to south gradient in ozoneconcentration as predicted by model calculations, butalso that some local photochemical production takesplace even at the remote Adriatic island far frompollution sources.     

On the Budget of OH Radicals and Ozone in an Urban Plume from the Decay of C5–C8 Hydrocarbons and NOx

Simultaneous measurements of ozone and ozoneprecursors were made during a field campaign atSchauinsland in the Black Forest and in the valleynorth of Schauinsland that channels the flow ofpolluted air from the city of Freiburg to the site.From the decay of hydrocarbons and NO_x between the twomeasuring sites and the known rate coefficients, theconcentration of OH radicals was calculated. From abudget analysis of OH and HO_x it is concluded that therelatively high OH concentrations (5–8 ×10⁶cm^-3) in the presence of high NO₂concentrations cannot be explained by the knownprimary sources. The budget can be closed if efficientrecycling of OH via HO₂ is assumed to occur andthat, based on the measured hydrocarbons, 2 HO₂molecules are formed for each OH radical that reactswith a hydrocarbon molecule. This assumption is inaccordance with the budget of O_x obtained from ourmeasurements and with results from earliermeasurements of alkylnitrates and peroxy radicals atSchauinsland. A possible conclusion is that the decayof precursors and production of photooxidants in urbanplumes proceeds at a faster rate than is currentlyassumed. The potential role of biogenichydrocarbons for the radical budget is alsodiscussed.     

High-Latitude Springtime Photochemistry. Part Ii: Sensitivity Studies of Ozone Production

A seven-year record of surface ozone measurements from Denali NationalPark, Alaska shows a persistent spring maximum. These data, combined withmeasurements of NO_x, hydrocarbons, O₃, and PANfrom a continental site in Alaska during the spring of 1995 are used as thebasis for a sensitivity study to explore tropospheric photochemistry in thisregion. Because of the relatively high concentrations of NO_x(mean of 116, median of 91 pptv), the net tendency was for photochemicalozone production. The range of net O₃ production for averageconditions measured at this site during spring is between 0.96–3.9ppbv/day depending on the assumptions used; in any case, this productionmust contribute to the observed springtime maximum in O₃.Model calculations showed that of the anthropogenic ozone precursors, onlyNO_x had a strong effect on the rate of ozone production; themeasured concentrations of anthropogenic hydrocarbons did not significantlyaffect the ozone budget. Naturally produced biogenic hydrocarbons, such asisoprene, may also have a significant effect on ozone production, even atconcentrations of a few 10's of pptv. An observed temperature-isoprenerelationship from a boreal site in Canada indicates that isoprene may bepresent during the Alaskan spring. Measurements of isoprene taken duringthe spring of 1996 suggest that reactive biogenic hydrocarbon emissionsbegin before the emergence of leaves on deciduous trees and that theconcentrations were sufficient to accelerate ozone production.