Bertrand Calpini

Regional levels of ozone in the troposphere over eastern Mediterranean

During the last 5 years, information on the regional tropospheric ozone levels over the eastern Mediterranean has become available but was confined to measurements at ground level. Here available information is expanded with measurements at two more rural ground level sites spanning 8° latitude, ozonesonde ascents, lidar observations, ship cruises, and aircraft flights. During wintertime the ozone monthly values are 10-20 ppbv higher than values at other European sites, while during summertime the values are comparable. This results in regional ozone background levels in the area that are above the European Union (EU) 32 ppb/24 hours phytotoxicity limit during the entire year. Late spring lidar observations show that south and southwestern synoptic flows which are associated with Saharan dust events result in lower ozone above the planetary boundary layer (PBL) by 20-35 ppbv as compared to these during northerly flows, which transport air from continental Europe. These lidar observations along with ship measurements during July show that ozone is enhanced 1.5-2.2 times in the continental outflow, when compared to aged maritime air or air from the African continent. These results along with ozonesonde observations suggest that ozone abatement in the area is largely beyond the control of regional emissions and can be controlled only with emission reductions on a European scale. During September, measured background NO and NO 2 levels between 3 and 4.5 km above sea level ranged from 1 to 221 pptv and from 102 to 580 pptv, respectively. The troposphere contains around 40-70 Dobson units of ozone during summer and around 20-30 Dobson units during winter.

Effect of Sea Breeze on Air Pollution in the Greater Athens Area. Part I: Numerical Simulations and Field Observations

Abstract Numerical simulations compared with field measurements are used to explain the effect of sea breezes on photochemical smog episodes in Athens during the Mediterranean Campaign of Photochemical Tracers on 12–14 September 1994. The numerical simulations, performed using a nonhydrostatic vorticity mesoscale model coupled to the Lurmann–Carter–Coyner photochemical module, are compared with ground-based lidar and aircraft measurements. The current analysis shows that the three selected days include the two main summertime flow patterns characteristic of the Athens peninsula, each of which lead to significantly different pollution amounts. On 12 and 13 September, a strong, northerly synoptic wind reduces the inland penetration of the sea breeze so that ozone concentrations within the greater Athens area remained low. In contrast, the weaker synoptic forcing on 14 September allowed the development of sea breezes over the whole peninsula and high ozone concentrations were found north and east of the city...

Experimental investigation of high-power single-pass Raman shifters in the ultraviolet with Nd:YAG and KrF lasers

Single-pass Raman cells pumped by either a quadrupled Nd:YAG (266-nm) laser or a KrF excimer laser are studied. The Raman-active gases comprise H(2), D(2), or CH(4), as well as a mixture of them, with the addition of He, Ne, or Ar. A parametric study, in which the Stokes conversion efficiency and the beam quality (M(2)) were measured, was made. The first Stokes efficiency increases and all the Stokes thresholds decrease with an increase in the lens focal length or the M(2) parameter of the pump beam. The quality of the Stokes beams deteriorates when the active-gas pressure increases but is improved by the addition of an inert gas. Laser-induced breakdown is shown to be a factor that limits the conversion efficiency and the quality of the Stokes beams. With a mixture of D(2), H(2), and Ar, a 10-15-mJ pulse energy is obtained (depending on the pump M(2) parameter) in the first Stokes beam of D(2) (289 nm) and H(2) (299 nm), with a full-angle divergence of 0.5 mrad (at 86% power).

Influence of the photomultiplier tube spatial uniformity on lidar signals

Measurements of the spatial uniformity of Hamamatsu H5783-06 photosensor modules were performed by the flying spot method. The results were used to simulate the influence of the photomultiplier tube on a lidar signal. A simple method for improving the spatial uniformity is proposed.

Low‐pressure chemical vapor deposition of copper: Dependence of the selectivity on the water vapor added to a hydrogen or helium carrier gas

The selectivity of copper deposition from copper (II) bis‐hexafluoroacetylacetonate on SiO2 patterned with a platinum seeding layer is studied as a function of the reagent gas mixture. On platinum, the copper film growth rate increases with the amount of water vapor in the gas flow, and is independent of the chemical nature of the carrier gas used (H2 or He). The selectivity of the copper deposition is significantly improved when using He rather than H2 as carrier gas, especially at high water vapor concentrations where rapid film growth can be obtained.

Total VOC reactivity in the planetary boundary layer 2. A new indicator for determining the sensitivity of the ozone production to VOC and NOx

A new indicator is proposed to det. whether tropospheric O3 prodn. in a specific area is limited by volatile org. compds. (VOC) or NOx. This indicator, tVOCOH/tNOxOH, describes the ratio of OH- lifetime vs. losses by reaction with VOC and NOx. Whereas tNOxOH can be obtained by conventional measurements, the new pump and probe OH approach makes it possible to also obtain tVOCOH. Indicator values above a threshold value of 0.2 +- 50% are representative of NOx-satd. conditions, where an increase of NOx emissions causes lower O3 prodn. For values <0.01, O3 prodn. is very insensitive to changes of VOC emissions. The robustness of this indicator against several parameters (temp., humidity, photolysis, initial O3 concn.) was tested in a box model and compared to the robustness of other earlier proposed indicators. In contrast to earlier proposed indicators, this new one is not based on photochem. produced long-lived species, but describes the instantaneous regime of an air parcel. Three-dimensional modeling showed this indicator is quite successful for estg. the impact of increased or reduced emissions on O3 concns. for each location in the modeled area. This will make it a very helpful tool for developing O3 abatement strategies.

Tropospheric ozone measurements over the Great Athens Area during the medcaphot-trace campaign with a new shot-per-shot dial instrument: experimental system and results

Within the MEDCAPHOT-TRACE program of the European Community for studying the photochem. air pollution over the Great Athens Area, we report on 3-D lidar measurements of tropospheric ozone. After a general presentation of the DIAL technique, the exptl. layout of our system which is equipped with a unique capability for real-time anal. of each individual optical backscattered signal is briefly described and its performance is assessed. The temporal evolution of the ozone concn. up to the top of the boundary layer is then followed over a few days. In particular, the first day of the photochem. smog episode is presented and commented.

Total VOC reactivity in the planetary boundary layer 1. Estimation by a pump and probe OH experiment

OH- radical reactivity with total volatile org. compds. (VOC), SkVOC[VOC], is directly obtained in the planetary boundary layer (PBL). A method is based on a perturbation technique where high initial OH- concns. are created by flash photolysis of O3 and subsequent reaction of O(1D) with H2O. Laser-induced fluorescence measures residual OH- concn. at different time delays after the perturbation (<100 ms) to obtain a direct est. of OH- lifetime (tOH) under different atm. conditions. For specific exptl. conditions, transport by wind may be neglected, and chem. processes governing OH- decay may be expressed using a detailed box model. With a simple chem. equation derived using tOH and complementary measurements of CO, O3, and NOx, an in-situ est. of SkVOC[VOC] in the PBL is retrieved with an uncertainty <20% vs. detailed box model calcns. This anal. was applied to lab. measurements with 3 synthetic NOx/VOC/O3 gas mixts.; retrieved OH- lifetimes and total VOC reactivity are discussed against model predictions.

Raman Frequency Shifting in a CH(4):H(2):Ar mixture pumped by the fourth harmonic of a Nd:YAG Laser.

Mixtures of methane, hydrogen, and argon (CH(4):H(2):Ar) were studied as UV Raman shifters for ozone differential absorption lidar application. They have higher photochemical stability than pure CH(4) and the capability to produce, with high enough efficiency, either first CH(4) Stokes or, simultaneously, CH(4) and H(2) first Stokes with equal energies. These mixtures can be used as an inexpensive replacement for D(2) or a more stable substitute for pure CH(4) in single-pass high-power Raman shifters.

Selective low pressure chemical vapor deposition of copper: Effect of added water vapor in hydrogen or helium carrier gas

The low pressure chemical vapor deposition (LPCVD) of copper from its bis‐hexafluoroacetylacetonate is studied on oxidized silicon substrates partially covered with a platinum seeding layer. With a known concentration of water vapor in the gas mixture, almost equal copper film growth rates are obtained when using either hydrogen or helium as carrier gas. For both carrier gases, an increase of the copper growth rate is observed with an increasing amount of water vapor added to the gas mixture, and deposition rates above 500 A/min are obtained. The chemical purity and electrical conductivity of the copper deposit are as high in the case of a helium carrier gas as in the case of a hydrogen carrier gas. Implications for the mechanism of copper LPCVD are discussed.