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Retrieval of cloud spherical albedo from top-of-atmosphere reflectance measurements performed at a single observation angle

The paper is aimed to the derivation of the simple analytical relationship between the cloud spherical albedo and the cloud reflection function in the visible. The relationship obtained can be used for the retrieval of the spherical albedo from backscattered solar light measurements performed by radiometers on geostationary and polar orbiting satellites. The example of the application of the technique to MODIS data is shown.
Aircraft pollution – a futuristic view

Impacts of NOx, H2O and aerosol emissions from a projected 2050 aircraft fleet are investigated using the Oslo CTM2, with emissions provided through the EU project SCENIC. The aircraft emission scenarios consist of emissions from subsonic and supersonic aircraft. In particular it is shown that aerosol emissions from such an aircraft fleet can have a relatively large impact on ozone, and possibly reduce the total atmospheric NOx by more than what is emitted by aircraft. Without aerosol emissions this aircraft fleet leads to similar NOx increases for subsonic (at 11–12 km) and supersonic (at 18–20 km) emissions, 1.35 ppbv and 0.83 ppbv as annual zonal means, respectively. H2O increases are also comparable at these altitudes: 630 and 599 ppbv, respectively. Tropospheric ozone increases are about 10 ppbv in the Northern Hemisphere due to emissions from subsonic aircraft. Increased ozone loss from supersonic aircraft at higher altitudes leads to ozone reductions of about 39 ppbv in the Northern Hemisphere and 22 ppbv in the Southern Hemisphere. The latter reduction is a result of transport of ozone depleted air from northern latitudes. When including aircraft aerosol emissions, NOx is reduced due to heterogeneous chemistry. The reduced NOx seems to counterweight the reduction of ozone from emissions of NOx and H2O above 20 km. At these altitudes the NOx (and thus ozone loss) reduction is large enough to give an aircraft emissions induced increase in ozone. In the height range 11–20 km altitude, however, ozone production is reduced. Heterogeneous reactions and reduced NOx enhances ClO, further enhancing ozone loss in the lower stratosphere. This results in a 14 ppbv additional reduction of ozone. Although supersonic aircraft have opposite effects on ozone in the upper and lower stratosphere, the change in ozone columns is clearly dominated by the upper stratospheric loss, thus supersonic aircraft aerosol emissions lead to enhanced ozone columns. The largest increase in the ozone column due to aerosol emissions is therefore seen in the Northern Hemispheric autumn and winter, giving a column increase of 4.5 DU. It is further found that at high northern latitudes during spring the heterogeneous chemistry on PSCs is particularly efficient, thereby increasing the ozone loss.
Air-to-sea flux of soluble iron: is it driven more by HNO3 or SO2? – an examination in the light of dust aging

Aeolian dust provides the major micronutrient of soluble Fe to organisms in certain regions of the global ocean. In this study, we conduct numerical experiments using the MOZART-2 atmospheric chemistry transport model to simulate the global distribution of soluble Fe flux and Fe solubility. One of the mechanisms behind the hypothesis of acid mobilization of Fe in the atmosphere is that the coating of acidic gases changes dust from hydrophobic to hydrophilic, a prerequisite of Fe mobilization. We therefore include HNO3, SO2 and sulfate (SO42−) as dust transformation agents in the model. General agreement in Fe solubility within a factor of 2 is achieved between model and observations. The total flux of soluble Fe to the world ocean is estimated to be 731–924×109 g yr−1, and the average Fe solubility is 6.4–8.0%. Wet deposition contributes over 80% to total soluble Fe flux to most of the world oceans. Special attention is paid to the relative role of HNO3 versus SO2 and sulfate. We demonstrate that coating by HNO3 produces over 36% of soluble Fe fluxes compared to that by SO2 and sulfate combined in every major oceanic basin. Given present trends in the emissions of NOx and SO2, the relative contribution of HNO3 to Fe mobilization may get even larger in the future.
Twenty-five years of continuous sulphur dioxide emission reduction in Europe

During the last twenty-five years European emission data have been compiled and reported under the Cooperative Programme for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants in Europe (EMEP) as part of the work under the UNECE Convention on Long-range Transboundary Air Pollution (LRTAP). This paper presents emission trends of SO2 reported to EMEP and validated within the programme for the period 1980–2004. These European anthropogenic sulphur emissions have been steadily decreasing over the last twenty-five years, amounting from about 55 Tg SO2 in 1980 to 15 Tg SO2 in 2004. The uncertainty in sulphur emission estimates for individual countries and years are documented to range between 3% and 25%. The relative contribution of European emissions to global anthropogenic sulphur emissions has been halved during this period. Based on annual emission reports from European countries, three emission reduction regimes have been identified. The period 1980–1989 is characterized by low annual emission reductions (below 5% reduction per year and 20% for the whole period) and is dominated by emission reductions in Western Europe. The period 1990–1999 is characterised by high annual emission reductions (up to 11% reduction per year and 54% for the whole period), most pronounced in Central and Eastern Europe. The annual emission reductions in the period 2000–2004 are medium to low (below 6% reduction per year and 17% for the whole period) and reflect the unified Europe, with equally large reductions in both East and West. The sulphur emission reduction has been largest in the sector Combustion in energy and transformation industries, but substantial decreases are also seen in the Non-industrial combustion plants together with the sectors Industrial combustion and Industrial production processes. The majority of European countries have reduced their emissions by more than 60% between 1990 and 2004, and one quarter have already achieved sulphur emission reductions higher than 80%. At European level, the total sulphur target for 2010 set in the Gothenburg Protocol (16 Tg) has apparently already been met by 2004. However, still half of the Parties to the Gothenburg Protocol have to reduce further their sulphur emissions in order to attain their individual country total emission targets for 2010. It is also noteworthy that, contrasting the Gothenburg Protocol requirements, a growing number of countries have recently been reporting increasing sulphur emissions, while others report only minor further decreases. The emission trends presented here are supported by different studies of air concentrations and depositions carried out within and outside the framework of the LRTAP Convention.
Multiwavelength and polarization lidar measurements of Asian dust layers over Tsukuba, Japan: a case study

Elastic and polarization lidar was used to measure the vertical profiles of aerosol backscattering coefficients at wavelengths of 355, 532, 735, and 1064 nm, and the depolarization ratio at 532 nm in order to study the aerosol properties in the free troposphere over Tsukuba, Japan, in 2006. An elevated dust layer was observed at altitudes between 3 and 8.5 km on 1 April during the Asian dust period. The wavelength exponents of the aerosol backscattering coefficient (k) were –0.1 to 0.5, and the depolarization ratio (δp) was 25% for the dust layer, suggesting the predominance of supermicrometer-sized (coarse mode) nonspherical particles. An aerosol layer observed at altitudes between 1.5 and 5 km on 19 October during the less-dust period exhibited the values of k=1.0 to 1.6 and δp=1 to 13%, suggesting the predominance of submicrometer-sized (fine mode) particles. In those layers, the values of k and δp varied with height; they were also negatively correlated, suggesting that the proportion of the coarse nonspherical particles to total particles varied. The particle size distributions estimated from the observed values and the theoretical computation revealed number mode radii of 0.3 &mum; for the coarse mode and 0.1 &mum; for the fine mode, assuming bimodal distribution. These results were consistent with those obtained from the sky-radiometer measurements, although they revealed another mode in the larger radius. The column volume concentration derived from the lidar was 48% lower than that derived from the sky-radiometer on 1 April and 16% lower on 19 October. The optical thickness derived from the lidar was 12% lower than that obtained from the sky-radiometer on 1 April and 29% higher on 19 October. Further case study is necessary to validate the method for estimating aerosol properties based on the lidar measurement.
On the efficiency of rocket-borne particle detection in the mesosphere

Meteoric smoke particles have been proposed as a key player in the formation and evolution of mesospheric phenomena. Despite their apparent importance still very little is known about these particles. Important questions concern the smoke number density and size distribution as a function of altitude as well as the fraction of charged particles. Sounding rockets are used to measure smoke in situ, but aerodynamics has remained a major challenge. Basically, the small smoke particles tend to follow the gas flow around the payload rather than reaching the detector if aerodynamics is not considered carefully in the detector design. So far only indirect evidence for the existence of meteoric smoke has been available from measurements of heavy charge carriers. Quantitative ways are needed that relate these measured particle population to the atmospheric particle population. This requires in particular knowledge about the size-dependent, altitude-dependent and charge-dependent detection efficiency for a given instrument. In this paper, we investigate the aerodynamics for a typical electrostatic detector design. We first quantify the flow field of the background gas, then introduce particles in the flow field and determine their trajectories around the payload structure. We use two different models to trace particles in the flow field, a Continuous motion model and a Brownian motion model. Brownian motion is shown to be of basic importance for the smallest particles. Detection efficiencies are determined for three detector designs, including two with ventilation holes to allow airflow through the detector. Results from this investigation show that rocket-borne smoke detection with conventional detectors is largely limited to altitudes above 75 km. The flow through a ventilated detector has to be relatively large in order to significantly improve the detection efficiency.
Model study of the cross-tropopause transport of biomass burning pollution

We present a modeling study of the troposphere-to-stratosphere transport (TST) of pollution from major biomass burning regions to the tropical upper troposphere and lower stratosphere (UT/LS). TST occurs predominately through 1) slow ascent in the tropical tropopause layer (TTL) to the LS and 2) quasi-horizontal exchange to the lowermost stratosphere (LMS). We show that biomass burning pollution regularly and significantly impacts the composition of the TTL, LS, and LMS. Carbon monoxide (CO) in the LS in our simulation and data from the Aura Microwave Limb Sounder (MLS) shows an annual oscillation in its composition that results from the interaction of an annual oscillation in slow ascent from the TTL to the LS and seasonal variations in sources, including a semi-annual oscillation in CO from biomass burning. The impacts of CO sources that peak when ascent is seasonally low are damped (e.g. Southern Hemisphere biomass burning) and vice-versa for sources that peak when ascent is seasonally high (e.g. extra-tropical fossil fuels). Interannual variation of CO in the UT/LS is caused primarily by year-to-year variations in biomass burning and the locations of deep convection. During our study period, 1994–1998, we find that the highest concentrations of CO in the UT/LS occurred during the strong 1997–1998 El Niño event for two reasons: i. tropical deep convection shifted to the eastern Pacific Ocean, closer to South American and African CO sources, and ii. emissions from Indonesian biomass burning were higher. This extreme event can be seen as an upper bound on the impact of biomass burning pollution on the UT/LS. We estimate that the 1997 Indonesian wildfires increased CO in the entire TTL and tropical LS (>60 mb) by more than 40% and 10%, respectively, for several months. Zonal mean ozone increased and the hydroxyl radical decreased by as much as 20%, increasing the lifetimes and, subsequently TST, of trace gases. Our results indicate that the impact of biomass burning pollution on the UT/LS is likely greatest during an El Niño event due to favorable dynamics and historically higher burning rates.
On using radon-222 and CO2 to calculate regional-scale CO2 fluxes

Because of its ubiquitous release on land and well-characterized atmospheric loss, radon-222 has been very useful for deducing fluxes of greenhouse gases such as CO2, CH4, and N2O. It is shown here that the radon-tracer method, used in previous studies to calculate regional-scale greenhouse gas fluxes, returns a weighted-average flux (the flux field F weighted by the sensitivity of the measurements to that flux field, f) rather than an evenly-weighted spatial average flux. A synthetic data study using a Lagrangian particle dispersion model and modeled CO2 fluxes suggests that the discrepancy between the sensitivity-weighted average flux and evenly-weighted spatial average flux can be significant in the case of CO2, due to covariance between F and f for biospheric CO2 fluxes during the growing season and also for anthropogenic CO2 fluxes in general. A technique is presented to correct the radon-tracer derived fluxes to yield an estimate of evenly-weighted spatial average CO2 fluxes. A new method is also introduced for correcting the CO2 flux estimates for the effects of radon-222 radioactive decay in the radon-tracer method.
Emission rate and chemical state estimation by 4-dimensional variational inversion

This study aims to assess the potential and limits of an advanced inversion method to estimate pollutant precursor sources mainly from observations. Ozone, sulphur dioxide, and partly nitrogen oxides observations are taken to infer source strength estimates. As methodology, the four-dimensional variational data assimilation technique has been generalised and employed to include emission rate optimisation, in addition to chemical state estimates as usual objective of data assimilation. To this end, the optimisation space of the variational assimilation system has been complemented by emission rate correction factors of 19 emitted species at each emitting grid point, involving the University of Cologne mesoscale EURAD model. For validation, predictive skills were assessed for an August 1997 ozone episode, comparing forecast performances of pure initial value optimisation, pure emission rate optimisation, and joint emission rate/initial value optimisation. Validation procedures rest on both measurements withheld from data assimilation and prediction skill evaluation of forecasts after the inversion procedures. Results show that excellent improvements can be claimed for sulphur dioxide forecasts, after emission rate optimisation. Significant improvements can be claimed for ozone forecasts after initial value and joint emission rate/initial value optimisation of precursor constituents. The additional benefits applying joint emission rate/initial value optimisation are moderate, and very useful in typical cases, where upwind emission rate optimisation is essential. In consequence of the coarse horizontal model grid resolution of 54 km, applied in this study, comparisons indicate that the inversion improvements can rest on assimilating ozone observations only, as the inclusion of NOx observations does not provide additional forecast skill. Emission estimates were found to be largely independent from initial guesses from emission inventories, demonstrating the potential of the 4D-var method to infer emission rate improvements. The study also points to the need for improved horizontal model resolution to more efficient use of NOx observations.
Vertical ozone measurements in the troposphere over the Eastern Mediterranean and comparison with Central Europe

Vertical ozone profiles measured in the period 1996–2002 in the framework of the MOZAIC project (Measurement of Ozone and Water Vapor by Airbus in Service Aircraft) for flights connecting Central Europe to the Eastern Mediterranean basin (Heraklion, Rhodes, Antalya) were analysed in order to evaluate the high rural ozone levels recorded in the Mediterranean area during summertime. The 77 flights during summer (JJAS) showed substantially (10–12 ppb, 20–40%) enhanced ozone mixing ratios in the lower troposphere over the Eastern Mediterranean frequently exceeding the 60 ppb, 8-h EU air quality standard, whereas ozone between 700 hPa and 400 hPa was only slightly (3–5 ppb, 5–10%) higher than over Central Europe. Analysis of composite weather maps for the high and low ozone cases, as well as back-trajectories and vertical profiles of carbon monoxide, suggest that the main factor leading to high tropospheric ozone values in the area is anticyclonic influence, in combination with a persistent northerly flow in the lower troposphere during summertime over the Aegean. On the other hand the lowest ozone levels are associated with low-pressure systems, especially the extension of the Middle East low over the Eastern Mediterranean area.