Jostein K. Sundet

Radiative forcing in the 21st century due to ozone changes in the troposphere and the lower stratosphere

ranging from 0.40 to 0.78 W m 2 on a global and annual average. The lower stratosphere contributes an additional 7.5–9.3 DU to the calculated increase in the ozone column, increasing radiative forcing by 0.15–0.17 W m 2 . The modeled radiative forcing depends on the height distribution and geographical pattern of predicted ozone changes and shows a distinct seasonal variation. Despite the large variations between the 11 participating models, the calculated range for normalized radiative forcing is within 25%, indicating the ability to scale radiative forcing to global-mean ozone column change. INDEX TERMS: 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0341 Atmospheric Composition and Structure: Middle atmosphere—constituent transport and chemistry (3334) Citation: Gauss, M., et al., Radiative forcing in the 21st century due to ozone changes in the troposphere and the lower stratosphere, J. Geophys. Res., 108(D9), 4292, doi:10.1029/2002JD002624, 2003.

Stratospheric ozone in 3‐D models: A simple chemistry and the cross‐tropopause flux

Two simple and computationally efficient models for simulating stratospheric ozone in three-dimensional global transport models are presented. The first, linearized ozone (or Linoz), is a first-order Taylor expansion of stratospheric chemical rates in which the ozone tendency has been linearized about the local ozone mixing ratio, temperature, and the overhead column ozone density. The second, synthetic ozone (or Synoz), is a passive, ozone-like tracer released into the stratosphere at a rate equivalent to that of the cross-tropopause ozone flux which, based on measurements and tracer-tracer correlations, we have calculated to be 475±120 Tg/yr. Linoz and Synoz have been evaluated in the UC Irvine chemical transport model (CTM) with three different archived meteorological fields: the Goddard Institute for Space Studies (GISS) general circulation model (GCM) version II′, the GISS GCM version II, and merged forecast data from the European Centre forecast model (EC/Oslo). Linoz produced realistic annual, cross-tropopause fluxes of 421 Tg/yr for the GISS II′ winds and 458 Tg/yr for the EC/Oslo winds; the GISS II winds produced an unrealistic flux of 790 Tg/yr. Linoz and Synoz profiles in the vicinity of the tropopause using the GISS II′ and EC/Oslo winds were found to be in good agreement with observations. We conclude that either approach may be adequate for a CTM focusing on tropospheric chemistry but that Linoz can also be used for calculating ozone fields interactively with the stratospheric circulation in a GCM. A future version of Linoz will allow for evolving background concentrations of key source gases, such as CH4 and N2O, and thus be applicable for long-term climate simulations.

Fresh air in the 21st century

Ozone is an air quality problem today for much of the worlds population. Regions can exceed the ozone air quality standards (AQS) through a combination of local emissions, meteorology favoring pollution episodes, and the clean-air baseline levels of ozone upon which pollution builds. The IPCC 2001 assessment studied a range of global emission scenarios and found that all but one projects increases in global tropospheric ozone during the 21st century. By 2030, near-surface increases over much of the northern hemisphere are estimated to be about 5 ppb (+2 to +7 ppb over the range of scenarios). By 2100 the two more extreme scenarios project baseline ozone increases of >20 ppb, while the other four scenarios give changes of -4 to +10 ppb. Even modest increases in the background abundance of tropospheric ozone might defeat current AQS strategies. The larger increases, however, would gravely threaten both urban and rural air quality over most of the northern hemisphere.

Model calculations of present and future levels of ozone and ozone precursors with a global and a regional model

Abstract Levels of key chemical pollutants in the atmosphere are calculated for present (1996) and future (2010) emission scenarios with the help of a global model (Oslo CTM2), and a regional model (EMEP Eulerian Photochemistry model) centered over Europe. Both models are three-dimensional (3D) Eulerian models and describe atmospheric transport based on the actual meteorological conditions for 1996. Boundary values of the chemical species for the regional model integrations are supplied by the global model. This paper assesses the importance of long-range Northern Hemispheric transport of ozone and its precursors to calculated concentrations at different height levels over Europe. Calculated 1996 ozone (O3) levels show good accordance with measurements for most of the year, but with a tendency to overestimate O3 at coastal cites. Sensitivity studies have been made with 2010 emission scenarios based on current legislation and reduction plans for Europe and USA, and IPCC scenario WP92a for the rest of the world. Significant reductions in emissions are expected in Europe and North America while increases are expected in other areas, and in particular over Southeast Asia. Model results show a general increase of the global tropospheric ozone levels with significant regional differences. Over Europe, an increase of free tropospheric ozone levels of the order of 10 ppbv can be expected in summer, resulting in boundary layer ozone levels over Europe of the order of 2 ppbv higher than with present free tropospheric levels. Even so, it can be expected that the ozone threshold values in Europe will be much less frequently exceeded in the future as a result of the foreseen reductions in the European emissions of ozone precursors.

Modeling the Annual Cycle of Sea Salt in the Global 3D Model Oslo CTM2: Concentrations, Fluxes, and Radiative Impact

A global three-dimensional chemical transport model (CTM) is used to model the yearly cycle of sea salt. Sea salt particles are produced by wind acting on the sea surface, and they are removed by wet and dry deposition. In this study, forecast meteorological data are taken from the ECMWF. The modeled concentrations are compared to measured concentrations at sea level, and both absolute values and monthly variations compare well with measurements. Radiation calculations have been performed using the same meteorological input data as the CTM calculations. The global, yearly average burden of sea salt is found to be 12 mg m22. This is within the range of earlier estimates that vary between 11 and 22 mg m22. The radiative impact of sea salt is calculated to be 2 1.1 Wm 22. The total, yearly flux of sea salt is estimated to be 6500 Tg yr 21.

Modeling the solar radiative impact of aerosols from biomass burning during the Southern African Regional Science Initiative (SAFARI-2000) experiment

[1] In this study, we model the radiative impact of biomass burning aerosols with meteorological data for the Southern African Regional Science Initiative (SAFARI-2000) experiment campaign period. Satellite, ground-based, and aircraft observations are used in the validation of the modeled aerosol optical depth (AOD), vertical profiles, and radiative impact of the aerosols. The modeled pattern and magnitude of the AOD is generally in good agreement with the observations. The meteorological conditions are found to be important in determining the distribution of the aerosols. The modeled radiative impact of the biomass aerosols compares well to measurements. During September 2000, the modeled radiative impact of biomass aerosols reaches 50 W m 2 locally. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; KEYWORDS: biomass burning, transport model, single scattering albedo, aerosol optical depth, aircraft measurements, radiative impact Citation: Myhre, G., T. K. Berntsen, J. M. Haywood, J. K. Sundet, B. N. Holben, M. Johnsrud, and F. Stordal, Modeling the solar radiative impact of aerosols from biomass burning during the Southern African Regional Science Initiative (SAFARI-2000) experiment, J. Geophys. Res., 108(D13), 8501, doi:10.1029/2002JD002313, 2003.

Chemical transport model ozone simulations for spring 2001 over the western Pacific: Comparisons with TRACE-P lidar, ozonesondes, and Total Ozone Mapping Spectrometer columns

[1] Two closely related chemical transport models (CTMs) employing the same highresolution meteorological data (180 km 180 km 600 m) from the European Centre for Medium-Range Weather Forecasts are used to simulate the ozone total column and tropospheric distribution over the western Pacific region that was explored by the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) measurement campaign in February–April 2001. We make extensive comparisons with ozone measurements from the lidar instrument on the NASA DC-8, with ozonesondes taken during the period around the Pacific Rim, and with TOMS total column ozone. These demonstrate that within the uncertainties of the meteorological data and the constraints of model resolution, the two CTMs (FRSGC/UCI and Oslo CTM2) can simulate the observed tropospheric ozone and do particularly well when realistic stratospheric ozone photochemistry is included. The greatest differences between the models and observations occur in the polluted boundary layer, where problems related to the simplified chemical mechanism and inadequate horizontal resolution are likely to have caused the net overestimation of about 10 ppb mole fraction. In the upper troposphere, the large variability driven by stratospheric intrusions makes agreement very sensitive to the timing of meteorological features. INDEX TERMS: 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere— composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; KEYWORDS: tropospheric ozone, tropopause, stratospheric intrusions, Western Pacific Citation: Wild, O., J. K. Sundet, M. J. Prather, I. S. A. Isaksen, H. Akimoto, E. V. Browell, and S. J. Oltmans, Chemical transport model ozone simulations for spring 2001 over the western Pacific: Comparisons with TRACE-P lidar, ozonesondes, and Total Ozone Mapping Spectrometer columns, J. Geophys. Res., 108(D21), 8826, doi:10.1029/2002JD003283, 2003.

Atmospheric degradation and global warming potentials of three perfluoroalkenes

The vapour phase reactions of perfluoropropene, CF3aCF ¼ CF2, and perfluorobuta-1,3-diene, CF2 ¼ CFaCF ¼ CF2, with OH, NO3 and O3 were studied at 29874 K and 74075 Torr using long-path FT-IR detection. The reactions with ozone are very slow, kCF3CFCF2þO3 ¼ð 6:271:5Þ� 10 @22 and kCF2CFCFCF2þO3 ¼ ð6:570:2Þ� 10 @21 cm 3 molecules @1 s @1 , and upper limits of 3 � 10 @15 cm 3 molecules @1 s @1 are reported for the NO3 reaction rate coefficients. The OH reaction rate coefficients were determined as kCF3CFCF2þOH ¼ð 2:670:7Þ� 10 @12 and kCF2CFCFCF2þOH ¼ð 1:170:3Þ� 10 @11 cm 3 molecules @1 s @1 ; perfluoropropene gave a nearly quantitative yield of CF3CFO and CF2O as organic products, while perfluorobuta-1,3-diene gave from 130% to 170% of CF2O. A chemistry transport model was applied to calculate the atmospheric distributions and lifetimes of the perfluoroalkenes; the global and yearly averaged lifetimes were calculated as 1.9 day for C2F4 and C4F6 and 6 days for C3F6. Quantitative infrared cross-sections of perfluoroethene, perfluoropropene, and perfluorobuta-1,3-diene have been obtained at 298 K in the region 100–2600 cm @1 . Radiative forcing calculations have been performed for these gases assuming either constant vertical profiles or the distribution derived from the chemistry transport model. The results show that the Global Warming Potentials are totally negligible for these compounds. r 2001 Elsevier Science Ltd. All rights reserved.

Uncertainties in the Radiative Forcing Due to Sulfate Aerosols

Radiative transfer calculations based on a new sulfate distribution from a chemistry-transport model simulation have been performed. A wide range of sensitivity experiments have been performed to illustrate the large uncertainty in the radiative forcing due to sulfate aerosols. The most important factors seem to be processes involved in the mixing of sulfate aerosols with other particles and uncertainties in the relative humidities. These factors can explain much of the large range in previous estimates of the radiative forcing due to sulfate aerosols reflected, for example, in the Intergovernmental Panel on Climate Change estimate. Included in this study is a simple subgrid-scale parameterization of relative humidity to investigate a potentially large uncertainty in the radiative forcing due to sulfate aerosol.

The human genomic melting map

In a living cell, the antiparallel double-stranded helix of DNA is a dynamically changing structure. The structure relates to interactions between and within the DNA strands, and the array of other macromolecules that constitutes functional chromatin. It is only through its changing conformations that DNA can organize and structure a large number of cellular functions. In particular, DNA must locally uncoil, or melt, and become single-stranded for DNA replication, repair, recombination, and transcription to occur. It has previously been shown that this melting occurs cooperatively, whereby several base pairs act in concert to generate melting bubbles, and in this way constitute a domain that behaves as a unit with respect to local DNA single-strandedness. We have applied a melting map calculation to the complete human genome, which provides information about the propensities of forming local bubbles determined from the whole sequence, and present a first report on its basic features, the extent of cooperativity, and correlations to various physical and biological features of the human genome. Globally, the melting map covaries very strongly with GC content. Most importantly, however, cooperativity of DNA denaturation causes this correlation to be weaker at resolutions fewer than 500 bps. This is also the resolution level at which most structural and biological processes occur, signifying the importance of the informational content inherent in the genomic melting map. The human DNA melting map may be further explored at http://meltmap.uio.no.