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We briefly present in this short paper some issues related to the development and the validation of the three-dimensional chemistry-transport model Polair. <br><br> Numerical studies have been performed in order to let Polair be an efficient and robust solver. This paper summarizes and comments choices that were made in this respect. <br><br> Simulations of relevant photochemical episodes were led to assess the validity of the model. The results can be considered as a validation, which allows next studies to focus on fine modeling issues. <br><br> A major feature of Polair is the availability of a tangent linear mode and an adjoint mode entirely generated by automatic differentiation. Tangent linear and adjoint modes grant the opportunity to perform detailed sensitivity analyses and data assimilation. This paper shows how inverse modeling is achieved with Polair.
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A modelling study of the formation of volatile particles in a combustor exhaust has been carried out in the frame of the PartEmis European project. A kinetic model has been used in order to investigate nucleation efficiency of the H<sub>2</sub>O-H<sub>2</sub>SO<sub>4</sub> binary mixture in the sampling system. A value for the fraction <IMG WIDTH="10" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" src="acp-4-439-img1.gif" ALT="$varepsilon$"> of the fuel sulphur S(IV) converted into S(VI) has been indirectly deduced from comparisons between model results and measurements. In the present study, <IMG WIDTH="10" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" src="acp-4-439-img1.gif" ALT="$varepsilon$"> ranges between roughly 2.5% and 6%, depending on the combustor settings and on the value assumed for the parameter describing sulphuric acid wall losses. Soot particles hygroscopicity has also been investigated as their activation is a key parameter for contrail formation. Growth factors of monodisperse particles exposed to high relative humidity (95%) have been calculated and compared with experimental results. The modelling study confirms that the growth factor increases as the soot particle size decreases.
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The three-dimensional photochemical model UAM-V is used to investigate the effects of various meteorological conditions and of the coarseness of emission inventories on the ozone concentration and ROG/NO<sub>x</sub> limitation of the ozone production in the Po Basin in the northern part of Italy. As a base case, the high ozone episode with up to 200ppb on 13 May 1998 was modelled and previously thoroughly evaluated with measurements gained during a large field experiment. Systematic variations in meteorology are applied to mixing height, air temperature, specific humidity and wind speed. Three coarser emission inventories are obtained by resampling from 3x3km<sup>2</sup> up to 54x54km<sup>2</sup> emission grids. The model results show that changes in meteorological input files strongly influence ozone in this area. For instance, temperature changes peak ozone by 10.1ppb/°C and the ozone concentrations in Milan by 2.8ppb/°C. The net ozone formation in northern Italy is more strongly temperature than humidity dependent, while the humidity is very important for the ROG/NO<sub>x</sub> limitation of the ozone production. For all meteorological changes (e.g. doubling the mixing height), the modelled peak ozone remains ROG limited. A strong change towards NO<sub>x</sub> sensitivity in the ROG limited areas is only found if much coarser emission inventories were applied. Increasing ROG limited areas with increasing wind speed are found, because the ROG limited ozone chemistry induced by point sources is spread over a larger area. Simulations without point sources tend to increase the NO<sub>x</sub> limited areas.
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During the Northern hemisphere winter season, biomass burning is widespread in West Africa, yet the total tropospheric column ozone values (<30DU) over much of the Tropical Atlantic Ocean (15°N-5°S) are relatively low. At the same time, the tropospheric column ozone values in the Southern Tropical Atlantic are higher than those in the Northern Hemisphere (ozone paradox). We examine the causes for low tropospheric column ozone values by considering the horizontal and vertical transport of biomass fire emissions in West Africa during November through March, using observed data which characterizes fires, aerosols, horizontal winds, precipitation, lightning and outgoing longwave radiation. We have found that easterly winds prevail in the lower troposphere but transition to westerly winds at pressure levels lower than 500hPa. A persistent anticyclone over West Africa at 700hPa is responsible for strong easterly winds, which causes a net outflow of ozone/ozone precursors from biomass burning in West Africa across the Atlantic Ocean towards South America. The lowest outgoing longwave radiation (OLR) and highest precipitation rates are generally found over the central Atlantic, some distance downstream of fires in West Africa making the vertical transport of ozone and ozone precursors less likely and ozone destruction more likely. However, lightning over land areas in Central Africa and South America can lead to enhanced ozone levels in the upper troposphere especially over the Southern tropical Atlantic during the Northern Hemisphere winter season.
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A sequential synthesis inversion method is described to estimate CO<sub>2</sub> sources from continuous atmospheric data. The sequential method makes the problem computationally feasible. The method is assessed using four-hourly synthetic concentration data generated from known sources. Multi-year mean sources and seasonal cycles are estimated with comparable quality as those from a traditional inversion of monthly mean data. Interannual variations in the estimated sources are closer to those of the known sources using the four-hourly data rather than monthly data. The computational cost of the basis function simulations can be reduced by generating responses that are only six months long. This does not significantly degrade the inversion results compared to using responses that are 12 months in length.
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Net vertical air mass export by thermally driven flows from the atmospheric boundary layer (ABL) to the free troposphere (FT) above deep Alpine valleys was investigated. The vertical export of pollutants above mountainous terrain is presently poorly represented in global chemistry transport models (GCTMs) and needs to be quantified. Air mass budgets were calculated using aircraft observations obtained in deep Alpine valleys. The results show that on average 3 times the valley air mass is exported vertically per day under fair weather conditions. During daytime the type of valleys investigated in this study can act as an efficient "air pump" that transports pollutants upward. The slope wind system within the valley plays an important role in redistributing pollutants. Nitrogen oxide emissions in mountainous regions are efficiently injected into the FT. This could enhance their ozone (O<sub>3</sub>) production efficiency and thus influences tropospheric pollution budgets. Once lifted to the FT above the Alps pollutants are transported horizontally by the synoptic flow and are subject to European pollution export. Forward trajectory studies show that under fair weather conditions two major pathways for air masses above the Alps dominate. Air masses moving north are mixed throughout the whole tropospheric column and further transported eastward towards Asia. Air masses moving south descend within the subtropical high pressure system above the Mediterranean.
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The main purpose of this study is to develop a methodology for a multidisciplinary nuclear risk and vulnerability assessment, and to test this methodology through estimation of a nuclear risk to population in the Northern European countries in case of a severe accident at the nuclear risk sites. For assessment of the probabilistic risk and vulnerability, a combination of social-geophysical factors and probabilities are considered. <P style="line-height: 20px;"> The main focus of this paper is the description of methodology for evaluation of the atmospheric transport of radioactive releases from the risk site regions based on the long-term trajectory modeling. The suggested methodology is given from the probabilistic point of view. The main questions stated are: What are probabilities and times for radionuclide atmospheric transport to different neighbouring countries and territories in case of the hypothetical accidental release at the nuclear risk site? Which geographical territories or countries are at the highest risk from the hypothetical accidental releases? <P style="line-height: 20px;"> To answer these questions we suggest applying the following research tools for probabilistic atmospheric studies. First tool is atmospheric modelling to calculate multiyear forward trajectories originated over the sites. Second tool is statistical analyses to explore temporal and spatial structure of calculated trajectories and evaluate different probabilistic impact indicators: atmospheric transport pathways, airflow, fast transport, typical transport time, maximum possible impact zone, maximum reaching distance, etc. These indicators are applicable for further GIS-analysis and integration to estimate regional risk and vulnerability in case of accidental releases at the risk sites and for planning the emergency response and preparedness systems.
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The effect of nitric acid on the equilibrium size distributions of upper tropospheric aerosols is calculated as a function of relative humidity. It is shown that HNO<sub>3</sub> concentrations above a few tenths of a ppb can cause substantial increases in haze mode particle concentrations at relative humidities at about 60% and above. The effect can be strongly magnified when letovicite particles are present in addition to sulfuric acid aerosols. Letovicite particles are less acidic than the sulfuric acid particles and so more nitric acid can be absorbed. This effect can be seen even at RH below 50% due to the lowering of the deliquescence RH of letovicite in the presence of gaseous nitric acid at low temperatures. We have also compared equilibrium calculations of the HNO<sub>3</sub> effect with observations of increased haze mode concentrations at relative humidities above 50% (Petzold et al., 2000). Nitric acid mixing ratios on the order of 0.5-2ppb may explain the observed increase of haze mode particles at least partially.
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The possible connections between the carbon balance of ecosystems and aerosol-cloud-climate interactions play a significant role in climate change studies. Carbon dioxide is a greenhouse gas, whereas the net effect of atmospheric aerosols is to cool the climate. Here, we investigated the connection between forest-atmosphere carbon exchange and aerosol dynamics in the continental boundary layer by means of multiannual data sets of particle formation and growth rates, of CO<sub>2</sub> fluxes, and of monoterpene concentrations in a Scots pine forest in southern Finland. We suggest a new, interesting link and a potentially important feedback among forest ecosystem functioning, aerosols, and climate: Considering that globally increasing temperatures and CO<sub>2</sub> fertilization are likely to lead to increased photosynthesis and forest growth, an increase in forest biomass would increase emissions of non-methane biogenic volatile organic compounds and thereby enhance organic aerosol production. This feedback mechanism couples the climate effect of CO<sub>2</sub> with that of aerosols in a novel way.
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A new method for measuring gas-phase naphthalene in the atmosphere is based on laser-induced fluorescence at low pressure. The fluorescence spectrum of naphthalene near 308 nm was identified. Naphthalene fluorescence quenching by N<IMG WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-563-img1.gif" ALT="$_{2}$">, O<IMG WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-563-img1.gif" ALT="$_{2}$"> and H<IMG WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-563-img1.gif" ALT="$_{2}$">O was investigated in the laboratory. No significant quenching was found for H<IMG WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-563-img1.gif" ALT="$_{2}$">O with mixing ratio up to 2.5%. The quenching rate of naphthalene fluorescence is (1.98<IMG WIDTH="15" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-563-img2.gif" ALT="$pm$">0.18) <IMG WIDTH="15" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-563-img3.gif" ALT="$times$">10<IMG WIDTH="26" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-563-img4.gif" ALT="$^{-11}$">cm<IMG WIDTH="10" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-563-img5.gif" ALT="$^{3}$">molecule<IMG WIDTH="20" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-563-img6.gif" ALT="$^{-1}$">s<IMG WIDTH="20" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-563-img6.gif" ALT="$^{-1}$"> for N<IMG WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-563-img1.gif" ALT="$_{2}$">, and (2.48<IMG WIDTH="15" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-563-img2.gif" ALT="$pm$">0.08)<IMG WIDTH="15" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-563-img3.gif" ALT="$times$">10<IMG WIDTH="26" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-563-img7.gif" ALT="$^{-10}$">cm<IMG WIDTH="10" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-563-img5.gif" ALT="$^{3}$">molecule<IMG WIDTH="20" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-563-img6.gif" ALT="$^{-1}$">s<IMG WIDTH="20" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-563-img6.gif" ALT="$^{-1}$"> for O<IMG WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-563-img1.gif" ALT="$_{2}$"> at 297 K. Instrument calibrations were performed with a range of naphthalene mixing ratios between 5 and 80 parts per billion by volume (ppbv, 10<IMG WIDTH="26" HEIGHT="34" ALIGN="MIDDLE" BORDER="0" src="acp-4-563-img8.gif" ALT="$^{-9})$">. In the current instrument configuration, the detection limit is estimated to be about 20 parts per trillion by volume (pptv, 10<IMG WIDTH="33" HEIGHT="34" ALIGN="MIDDLE" BORDER="0" src="acp-4-563-img9.gif" ALT="$^{-12})$"> with 2<IMG WIDTH="13" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" src="acp-4-563-img10.gif" ALT="$sigma $"> confidence and a 1-min integration time. Measurements of atmospheric naphthalene in three cities, Nashville, TN, Houston, TX, and New York City, NY, are presented. Good correlation between naphthalene and major anthropogenic pollutants is found.
