Vertical column abundances and seasonal cycle of acetylene,C2H2, above the Jungfraujoch station,derived from IR solar observations

Monthly mean total vertical column abundances of acetylene have been determined from series of infrared solar spectra recorded at the Jungfraujoch station, Switzerland, between June 1986 and April 1991. The data have been obtained by nonlinear least-squares fittings of the ₅ band R19 transition of C₂H₂ at 776.0818 cm^-1. The average of 22 monthly mean total vertical columns of C₂H₂ retrieved during that time interval of almost 5 years was found to be equal to (1.81±0.12)×10¹⁵ molec/cm², which corresponds to an average mixing ratio of (0,22±0.013) ppbv (parts per billion by volume) in a troposphere extending from the altitude of the station (3.58 km), up to 10.5 km. Despite the large variability found from year to year, a least-squares sine fit to the data reveals a seasonal variation with an amplitude of about ±40% of the mean; the maximum occurs during mid-winter and the minimum in the summer. The present results are compared critically with similar in-situ data found in the literature. A sinusoidal fit to all such free troposphere measurements made in-situ between 30°N and 60°N indicates good agreement in shape and phase with the seasonal variation derived above the Jungfraujoch, but their average column abundance, 2.3×10¹⁵ molec/cm², is about 30% higher; this difference is explained on the basis of non-upwelling meteorological conditions generally prevailing during ground-based remote solar observations.     

Simultaneous Measurements of Black Carbon, PM10, Ozone and NOx Variability at a Locally Polluted Island in the Southern Tropics

This paper shows a comparative study of particle and surface ozone concentration measurements undertaken simultaneously at two distinct semi-urban locations distant by 4 km at Saint-Denis, the main city of La Réunion island (21.5° S, 55.5° E) during austral autumn (May 2000). Black carbon (BC) particles measured at La Réunion University, the first site situated in the suburbs of Saint-Denis, show straight-forward anti-correlation with ozone, especially during pollution peaks ( 650 ng/m³ and 15 ppbv, for BC and ozone respectively) and at night-time (90 ng/m³ and 18.5 ppbv, for BC and ozone respectively). NO_x (NO and NO₂) and PM₁₀ particles were also measured in parallel with ozone at Lislet Geoffroy college, a second site situated closer to the city centre. NO_x and PM₁₀ particles are anti-correlated with ozone, with noticeable ozone destruction during peak hours (mean 6 and 9 ppbv at 7 a.m. and 8 p.m. respectively) when NO_x and PM₁₀ concentrations exhibit maximum values. We observe a net daytime ozone creation (19 ppbv, O₃ +4.5 ppbv), following both photochemical and dynamical processes. At night-time however, ozone recovers (mean 11 ppbv) when anthropogenic activities are lower ([BC] 100 ng/m³). BC and PM₁₀ concentration variation obtained during an experiment at the second site shows that the main origin of particles is anthropogenic emission (vehicles), which in turn influences directly ozone variability. Saint-Denis BC and ozone concentrations are also compared to measurements obtained during early autumn (March 2000) at Sainte-Rose (third site), a quite remote oceanic location. Contrarily to Saint-Denis observations, a net daytime ozone loss (14.5 ppbv at 4 p.m.) is noticed at Sainte-Rose while ozone recovers (17 ppbv) at night-time, with however a lower amplitude than at Saint-Denis. Preliminary results presented here are handful data sets for modelling and which may contribute to a better comprehension of ozone variability in relatively polluted areas.     

Tropospheric ozone and oxides of nitrogen over the north-western Pacific in summer

In summer, atmospheric ozone was measured from an aircraft platform simultaneously with nitric oxide (NO), oxides of nitrogen (NO _y ), and water vapor over the Pacific Ocean in east Asia from 34° N to 19° N along the longitude of 138±3°E. NO _y was measured with the aid of a ferrous sulfate converter. The altitude covered was from 0.5 to 5 km. A good correlation in the smoothed meridional distributions between ozone and NO _y was seen. In particular, north of 25° N, ozone and NO _y mixing ratios were considerably higher than those observed in tropical marine air south of 25° N. NO _y and O₃ reached a minimum of 50 pptv and 4 ppbv respectively in the boundary layer at a latitude of 20° N. The NO concentration between 2 and 5 km at the same latitude was 30 pptv. The profiles of ozone and water vapor mixing ratios were highly anti-correlated between 25° N and 20° N. In contrast, it was much poorer at the latitude of 33° N, suggesting a net photochemical production of ozone there.     

Variations in atmospheric CO2 at the Meteorological Research Institute, Tsukuba, Japan

Since April 1986, measurements of the CO₂ concentration in the surface air have been conducted at the Meteorological Research Institure (MRI, 36°04 N, 140°07 E, 25 m above sea level) in Tsukuba, located 50 km northeast of Tokyo, Japan. The CO₂ data measured over times between 11:00 Japan Standard Time (JST) and 16:00 JST (C _N ) were considered to be representative of the air (within a few ppmv) in the planetary boundary layer. To evaluate the representative CO₂ level on a spatial scale larger than that of the C _N record, the CO₂ data with hour-to-hour variation less than 1 ppmv were selected (C _P ). Comparison of these data with those of Ryori (39°02 N, 141°50 E), a continental station operated by the Japan Meteorological Agency, indicates that the C _P record provides a representative CO₂ level in the air on spatial scales of at least a few hundred kilometers.The C _N record allows an investigation of the internanual changes in photosynthesis/respiration against changes in climatological parameters. Within a small temperature anomaly (ca.±1 °C) respiration is sensitive to the temperature change, while photosynthesis is less sensitive. When the temperature anomaly is large, however, photosynthesis and respiration tend to be competitive.     

Carbonyl sulfide emissions from biomass burning in the tropics

Carbonyl sulfide emissions from biomass burning have been studied during field experiments conducted both in an African savanna area (Ivory Coast) and rice fields, central highland pine forest and savanna areas in Viet-Nam. During these experiments CO₂, CO and C₂H₂ or CH₄ have also been also monitored. COS values range from 0.6 ppbv outside the fires to 73 ppbv in the plumes. Significant correlations have been observed between concentrations of COS and CO (R ²=0.92,n=25) and COS and C₂H₂ (R ²=0.79,n=26) indicating a COS production during the smoldering combustion. COS/CO₂ emission factors (COS/CO₂) during field experiments ranged from 1.2 to 61×10^–6 (11.4×10^–6 mean value). COS emission by biomass burning was estimated to be up to 0.05 Tg S/yr in tropics and up to 0.07 Tg S/yr on a global basis, contributing thus about 10% to the global COS flux. Based on the S/C ratio measured in the dry plant biomass and the COS/CO₂ emission factor, COS can account for only about 7% of the sulfur emitted in the atmosphere by biomass burning.     

Reactions of alkoxy radicals under atmospheric conditions: The relative importance of decomposition versus reaction with O2

The reactions of alkoxy radicals determine to a large extent the products formed during the atmospheric degradations of emitted organic compounds. Experimental data concerning the decompositions, 1,5-H shift isomerizations and reactions with O₂ of several classes of alkoxy radicals are inconsistent with literature estimations of their absolute or relative rate constants. An alternative, although empirical, method for assessing the relative importance under atmospheric conditions of the reactions of alkoxy radicals with O₂ versus decomposition was derived. This estimation method utilizes the differences in the heats of reaction, (H)=(H_{decomposition}–H_{O 2 reaction}), between these two reactions pathways. For (H)[22–0.5(H_{O 2 reaction})], alkoxy radical decomposition dominates over the reaction with O₂ at room temperature and atmospheric pressure of air, while for (H)[25-0.5(H_{O 2 reaction})], the O₂ reaction dominates over decomposition (where the units of H are in kcal mol^–1). The utility and shortcomings of this approach are discussed. It is concluded that further studies concerning the reactions of alkoxy radicals are needed.     

Stratospheric N2O5, CH4, and N2O profiles from IR solar occultation spectra

Stratospheric volume mixing ratio profiles of N₂O₅, CH₄, and N₂O have been retrieved from a set of 0.052 cm^–1 resolution (FWHM) solar occultation spectra recorded at sunrise during a balloon flight from Aire sur l'Adour, France (44° N latitude) on 12 October 1990. The N₂O₅ results have been derived from measurements of the integrated absorption by the 1246 cm^–1 band. Assuming a total intensity of 4.32×10^–17 cm^–1/molecule cm^–2 independent of temperature, the retrieved N₂O₅ volume mixing ratios in ppbv (parts per billion by volume, 10^–9), interpolated to 2 km height spacings, are 1.64±0.49 at 37.5 km, 1.92±0.56 at 35.5 km, 2.06±0.47 at 33.5 km, 1.95±0.42 at 31.5 km, 1.60±0.33 at 29.5 km, 1.26±0.28 at 27.5 km, and 0.85±0.20 at 25.5 km. Error bars indicate the estimated 1- uncertainty including the error in the total band intensity (±20% has been assumed). The retrieved profiles are compared with previous measurements and photochemical model results.Laboratoire associé aux Universités Pierre et Marie Curie et Paris Sud.     

Airborne and lidar measurements of aerosol and cloud particles in the troposphere over Alert Canada in April 1986

As a component of the Canadian Arctic Haze Study, held coincident with the second Arctic Gas and Aerosol Sampling Program (AGASP II), vertical profiles of aerosol size distribution (0.17 m), light scattering parameters and cloud particle concentrations were obtained with an instrumented aircraft and ground-based lidar system during April 1986 at Alert. Northwest Territories. Average aerosol number concentrations range from about 200 cm^–3 over the Arctic ice cap to about 100 cm^–3 at 6 km. The aerosol size spectrum is virtually free of giant or coarse aerosol particles, and does not vary significantly with altitude. Most of the aerosol volume is concentrated in the 0.17–0.50 m size range, and the aerosol number concentration is found to be a good surrogate for the SO₄ ⁼ concentration of the Arctic haze aerosol. Comparison of the aircraft and lidar data show that, when iced crystal scattering is excluded, the aerosol light scattering coefficient and the lidar backscattering coefficient are proportional to the Arctic haze aerosol concentration. Ratios of scattering to backscattering, scattering to aerosol number concentration, and backscattering to aerosol number concentration are 15.3 steradians, 1.1×10^–13 m², and 4.8×10^–15 m² sr^–1, respectively. Aerosol scattering coefficients calculated from the measured size distributions using Mie scattering agree well with measured values. The calculations indicate the aerosol absorption optical depth over 6 km to range between 0.011 and 0.018. The presence of small numbers of ice crystals (10–20 crystals 1^–1 measured) increased light scattering by over a factor of ten.     

Nitrogen dioxide column content measurements made from an aircraft between 5° and 82°N

In the first two weeks of May 1981, the research jet of the German Aerospace Research Establishment (DFVLR) was charted to fly a meridional section between 5° and 82°N. A scanning filter photometer, developed at the Max Planck Institut für Aeronomie to measure column content values of atmospheric ozone and nitrogen dioxide, using ultra violet and visible absorption techniques, constituted part of the experimental payload for this campaign that was called SIMOC. The vertical NO₂ column content above the aircraft, flying at approximately 10 km, was found to decrease rapidly from 6.9×10¹⁵ molecules cm^-2 to 2.5×10¹⁵ molecules cm^-2 around 50°N and then to increase again north of 75°N. A sharp rise in the NO₂ content was observed south of the subtropical jet but this could possibly be due to the increased depth of the troposphere above the aircraft in these regions.     

Latitudinal variation of measured NO2 photolysis frequencies over the Atlantic Ocean between 50° N and 30° S

Using a filter radiometer, the meridional profile of the NO₂ photolysis frequency, J(NO₂), was measured between 50° N and 30° S during the cruise ANTVII/1 September/October 1988 of the research vessel Polarstern on the Atlantic Ocean. Simultaneously, global broadband irradiance and acrosol were monitored. Clean marine background air with low aerosol loads (b _sp=(1–2)×10^-5 m^-1) was encountered at the latitudes 25° N–30° N and 18° S–27° S, respectively. Under these conditions and an almost cloudless sky J(NO₂) reached 7.3×10^-3 s^-1 (2 sr) for a zenith angle of 30°. Between 30° N and 30° S, the latitudinal variation of the J(NO₂) noontime maxima was less than ± 10%, while the mean value at noon was 7.8×10^-3 s^-1. For the set of all data between 50° N and 30° S, a nearly linear correlation of J(NO₂) vs. global broadland irradiance was found. The slope of (8.24±0.03)×10^-5 s^-1/mW cm^-2 agrees within 10% with observations in Jülich (51° N, 6.2° E).     

Kinetics of the Reactions of IO with HO2 and O(3P)

A discharge-flow tube coupled with resonance fluorescence and chemiluminescence detection has been used to investigate the reactions IO + HO₂ products (1) and IO + O(³P) I + O₂(2), at T = 296 ± 1 K and P = 1.7 - 2 Torr. The rate constants k_-1 and k₂ have been found to be (7.1 ± 1.6) × 10^-11 cm³ molecule^-1 s^-1 and (1.35 ± 0.15) × 10^-10 cm³ molecule^-1 s^-1, respectively.     

Altitude profile and sunset decay measurements of stratospheric nitric oxide

In July 1974 an NO/O₃ chemiluminescent instrument was used to obtain measurements of NO in the stratosphere during two balloon flights launched from Churchill (59°N, 95°W). On the first flight, an altitude profile was obtained in which the NO volume mixing ratio was observed to increase from 0.3 to 2.7 ppbv between 19 and 29.5 km. On the second flight, the mixing ratio was observed to increase from 0.25 to 2.7 ppbv between 19 and 29 km and to remain almost constant at about 2.7 ppbv from 29 to 34.5 km. On this flight, the sunset decay of NO was also obtained while the payload was at a constant float altitude of 34.5 km. These decay measurements are compared satisfactorily with the results obtained from a time dependent stratospheric model.     

Measurement of PAN in the Polluted Boundary Layer and Free Troposphere Using a Luminol-NO2 Detector Combined with a Thermal Converter

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.     

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.     

Sampling of Chemical Constituents in Electrically Active Convective Systems: Results and Cautions

On flights of a P3-B turboprop and a WB-57F jet aircraft within thunderstorm systems, short term spikes (1–2 sec or less in duration) in NO and O₃ were recorded and are attributed to hot or cold discharges occurring on the aircraft fuselage or air sampling inlets. One such spike of only ∼300 msec duration reached 325 ppbv of NO on the flight of the jet aircraft while at 13.8 km altitude. In a lightning flash to the P3-B aircraft, production of NO (expected) and NO₂ (unexpected) were directly observed. The NO production was ∼ 1.7 x 10²² molecules/m of flash length. In the P3-B flight at 5.5 km altitude and over a distance of ∼ 275 km within a highly electrically active thunderstorm complex in the equatorial central Pacific Ocean, there was no evidence of production of O₃ or CO by lightning flashes or by any type of hot or cold discharge involved in the development of free-air lightning flashes.     

Field measurements of NO and NO2 emissions from fertilized and unfertilized soils

Field measurements of NO and NO₂ emissions from soils have been performed in Finthen near Mainz (F.R.G.) and in Utrera near Seville (Spain). The applied method employed a flow box coupled with a chemiluminescent NO _x detector allowing the determination of minimum flux rates of 2 g N m^-2 h^-1 for NO and 3 g m^-2 h^-1 for NO₂.The NO and NO₂ flux rates were found to be strongly dependent on soil surface temperatures and showed strong daily variations with maximum values during the early afternoon and minimum values during the early morning. Between the daily variation patterns of NO and NO₂, there was a time lag of about 2 h which seem to be due to the different physico-chemical properties of NO and NO₂. The apparent activation energy of NO emission calculated from the Arrhenius equation ranged between 44 and 103 kJ per mole. The NO and NO₂ emission rates were positively correlated with soil moisture in the upper soil layer.The measurements carried out in August in Finthen clearly indicate the establishment of NO and NO₂ equilibrium mixing ratios which appeared to be on the order of 20 ppbv for NO and 10 ppbv for NO₂. The soil acted as a net sink for ambient air NO and NO₂ mixing ratios higher than the equilibrium values and a net source for NO and NO₂ mixing ratios lower than the equilibrium values. This behaviour as well as the observation of equilibrium mixing ratios clearly indicate that NO and NO₂ are formed and destroyed concurrently in the soil.Average flux rates measured on bare unfertilized soils were about 10 g N m^-2 h^-1 for NO₂ and 8 g N m^-2 h^-1 for NO. The NO and NO₂ flux rates were significantly reduced on plant covered soil plots. In some cases, the flux rates of both gases became negative indicating that the vegetation may act as a sink for atmospheric NO and NO₂.Application of mineral fertilizers increased the NO and NO₂ emission rates. Highest emission rates were observed for urea followed by NH₄Cl, NH₄NO₃ and NaNO₃. The fertilizer loss rates ranged from 0.1% for NaNO₃ to 5.4% for urea. Vegetation cover substantially reduced the fertilizer loss rate.The total NO _x emission from soil is estimated to be 11 Tg N yr^-1. This figure is an upper limit and includes the emission of 7 Tg N yr^-1 from natural unfertilized soils, 2 Tg N yr^-1 from fertilized soils as well as 2 Tg N yr^-1 from animal excreta. Despite its speculative character, this estimation indicates that NO _x emission by soil is important for tropospheric chemistry especially in remote areas where the NO _x production by other sources is comparatively small.     

Simultaneous measurements of peroxy and nitrate radicals at Schauinsland

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.     

Measurement of the photodissociation coefficient of NO2 in the atmosphere: II,stratospheric measurements

The photodissociation coefficient of NO₂, J _{NO 2}, has been measured from a balloon platform in the stratosphere. Results from two balloon flights are reported. High Sun values of J _{NO 2} measured were 10.5±0.3 and 10.3±0.3×10^-3 s^-1 at 24 and 32 km respectively. The decrease in J _{NO 2} at sunset was monitored in both flights. The measurements are found to be in good agreement with calculations of J _{NO 2} using a simplified isotropic multiple scattering computer routine.     

On the scavenging of gaseous nitrogen compounds by large and small rain drops I. A wind tunnel and theoretical study of the uptake and desorption of NH3 in the presence of CO2

An experimental study has been carried out in the Mainz vertical wind tunnel to determine the rate at which NH₃ in the presence of CO₂ is absorbed by freely suspended water drops. The experimental uptake rates were found to be in good agreement with the rates predicted by the Kronig-Brink convective diffusion model and, for gas concentrations in the ppbv range also by the model in which it is assumed that the absorbed gas is well mixed inside the drop (henceforth called well mixed model). The same conclusion was shown to apply also to the desorption of NH₃ from a drop previously exposed to NH₃. The latter result is in contrast to the desorption of SO₂ which must be described by a model which accounts for the diffusion of the species inside the drop. Comparison of our experimental results with theory show further that the uptake of NH₃ in presence of CO₂ is significantly overestimated if the slow reaction CO_2(aq)+H₂OHCO ₃ ^– +H⁺ is neglected in the theoretical computation.     

Free convection scaling over the ocean derived from buoy measurements during gate

The structure of atmospheric turbulence in the surface layer over the open ocean is examined under conditions of local free convection. The raw data consist of profile and fluctuation measurements of wind and temperature as obtained from a meteorological buoy. For near neutral conditions and for waves running approximately along the wind direction, wave-induced wind fluctuations can be described by a simplified linear theory based on Miles (1957). In this case, the spectrum of wind velocity is given as the sum of two parts; for the turbulent part, the parameterization as obtained by Kaimal et al. (1972) applies, while the wave-induced part is parameterized using a simplification of Miles' linear theory. For cases of local free convection, the measurements of the vertical component of the wind velocity are well described by similarity theory; as expected, _w /(-uw)^1/2 is proportional to (- z/L)^1/3. In order to scale the longitudinal wind velocity component, it seems to be reasonable to extend the list of relevant parameters by the height of the mixed layer z _i. We obtain _u /(- uw)^1/2 (z/z _i)^1/3(- z/L)^1/3 with only a poor correlation coefficient of r = 0.6. Overall, the results of local free convection scaling obtained from direct measurements show good agreement with those obtained from profile measurements. A comparison between direct and indirect determination of turbulent fluxes of momentum shows an unexplained difference of about 20%. This discrepancy is mainly due to a gap in the uw-cospectrum at the swell frequency.