A11F-01
GEOmon: Towards an integrated system for Earth Observation
Changes in the atmospheric composition of many chemically and radiatively important gases not only affect the climate, but also have significant impacts on human health, ecosystems and the hy-drological cycle. To understand and predict these long-term changes, high quality integrated ob-servations are required. The EU FP6 project GEOmon is a first step to build a future integrated pan-European Atmospheric Observing System dealing with systematic observations of long-lived greenhouse gases, reactive gases, aerosols, and stratospheric ozone. To achieve this, quality as-sured, harmonized, and representative long-term data sets collected by in-situ and remote sensing instruments (ground based and aircraft) at the European and global level have to be integrated with satellite measurements. As part of the European observation system (GMES) and of IGACO (Integrated Global Atmospheric Chemistry Observations), GEOmon is contributing to the GEOSS (Global Earth Observation System of Systems) aims on air quality and climate change. This paper provides examples of basic investigations within GEOmon activity 2 (Reactive Gases) that are essential for building an integrated observation system such as the analysis of representa-tiveness of in-situ sites, field intercomparisons of ground-based remote sensing profiles, including in-situ data and comparisons of integrated profiles as well as vertically integrated in-situ data, with vertical tropospheric profiles and columns of satellites. In order to determine and understand trends of reactive compounds, harmonized long term data series as well as integrated datasets will be used for the evaluation with selected state-of-the-art chemical transport models used in the framework of GEOmon to simulate the long-term evolution of the atmospheric composition.
A11F-02
Intra-Asian Air Pollutions and Their Transport: Characterization From Ground Based Observation
We present the observation and analysis of surface air pollutions at the inflow, source, and outflow regions of Asia. Data of ozone, carbon monoxide, and black carbon from several sites in Asia including China, Japan, Siberia, Kyrgyz have been collected and analyzed. It is found that the ozone from East Asian source region, three mountain sites (Mt. Tai, Mt. Hua, and Mt. Huang) in central eastern China, show the highest mixing ratios. In 2004, their annual averages are 56.0, 48.6, 50.4 ppb respectively at Mt. Tai, Mt. Hua, and Mt. Huang while the annual averages at the inflow and outflow are significantly lower. Episodes of ozone higher than 100 ppb have also been frequently observed in source regions. It is found that ozone and carbon monoxide in source regions are mainly controlled by large-scale anthropogenic emissions and East Asian monsoon. Meanwhile, black carbon variations are more subject to smaller scale emission and transport. Looking into transport components from trajectory analysis, when the continental air masses are transported from inflow region of Eurasia to source region in China, annual ozone increased of 17 ppb have been observed. The maximum buildups, 40-46 ppb, appear in June were estimated. Within source region, we found the ozone increases with the longer residence time over the polluted domain in central eastern China. The increasing rates are found highest during the ozone peak season in May-June, 31 ppb/day at Mt. Tai and 12 ppb/day at Mt. Huang. It is estimated that central eastern China sources contribute 34-42% of ozone at Mt. Tai and 8-14% at Mt. Huang during the ozone peak season. We also verify the evidences of direct pollution transport from central eastern China to an outflow site in Okinawa Island where 31 ppb increases of ozone were observed when the pollution episodes from central eastern China reached the site in May-June 2004. More investigation on carbon monoxide and black carbon are underway.
A11F-03 INVITED
Tropospheric Ozone Changes
Growing recognition of the role of "background" tropospheric ozone on climate forcing and as a boundary condition for air quality changes highlights the importance of obtaining a broad picture of tropospheric ozone changes. Key surface and ozonesonde observing sites with tropospheric ozone measurement records longer than ~15 years have been selected to characterize longer term tropospheric ozone changes over broad geographic regions. The sites chosen vary from those with minimal impact by local ozone pollution sources to those that are in relatively close proximity to ozone precursor emissions and are thus affected in part by these sources. Consideration is given to the extent to which various time series represent broad geographic scales. Some series with more limited geographic representativeness can provide valuable information because of the length of the record, particularly in an underrepresented region. The vertical profile information from the ozonesonde stations, which have some of the longest tropospheric ozone records, provides a unique perspective on ozone in the free troposphere that is much less influenced by more local conditions. The general slowing or flattening of ozone increases seen at a number of locations beginning in the early 1990s has generally continued. At Naha, Japan there has been a significant increase in recent years that has not been seen at other Japanese ozonesonde locations. At high latitudes over North America a decade long decline in tropospheric ozone beginning in the 1980s has generally reversed with amounts now similar to those at the beginning of the record. In the S.H. several sites in the mid latitudes have shown significant increases. Although some overall patterns on changes emerge on regional scales and in some cases on continental scales, more general conclusions on hemispheric and global scales do not emerge. This is likely consistent with the varied pattern of ozone lifetimes, precursor emission changes, and transport regimes that influence tropospheric ozone trends.
A11F-04
The Contribution of Inter-continental Transport to Surface Ozone in the U.S: A Multi-model vs. Observations Assessment
The Task Force on Hemispheric Transport of Air Pollution (HTAP) was established by the UNECE Convention on Long-range Transboundary Air Pollution to develop a fuller understanding of hemispheric transport of ozone (O3), particulate matter, mercury and POPs. In support of HTAP, a number of groups have participated in a series of model experiments for the year 2001 in which anthropogenic emissions of ozone precursors were decreased by 20% in four northern mid-latitude source regions (North America, Europe, East Asia, and South Asia). We focus here on evaluating these simulations and use them to assess intercontinental influences on surface ozone over the continental U.S. Model calculated maximum daily 8-hour average (MDA8) O3 is evaluated with observations from the U.S. EPA's Clean Air Status and Trends Network (CASTNet). The 16-model mean shows a positive bias in most eastern sites that is strongest in summer (up to 25 ppbv above observed MDA8 values). Ensemble mean biases are generally smaller at sites in the western U.S., but correlations are weaker at the higher- altitude (>1.5 km ASL) western sites, particularly in summer. This is most likely caused by the inability of global models to resolve local flows in regions with sharp topographic features. The impact of inter-continental transport on surface O3 throughout the U.S. is quantified by summing the results from the experiments in which anthropogenic emissions of O3 precursors were decreased by 20% in the three foreign source regions. In general, the greatest declines in MDA8 O3 (~0.9 ppbv) are observed at high-altitude sites in the western U.S. in response to East Asian and European emissions reductions. The decline in MDA8 O3 due to foreign emission reductions is fairly constant across the range of MDA8 values in the western U.S. However, in the Midwest and eastern U.S., the greatest declines in MDA8 O3 (~0.6 ppbv) tend to occur towards the lower end of O3 distributions (at concentrations < ~45ppbv). In contrast, a 20% reduction in North American O3 precursor emissions caused a decline in MDA8 O3 of ~4-7 ppbv in the eastern U.S. and ~2-3 ppbv in the western U.S., with the greatest decreases at the high end of the O3 distribution in summer.
A11F-05
Observed and Modeled Decadal Trends in Ozone Concentrations at Northern mid- Latitudes
In situ measurements of ozone concentrations at both surface sites and from aircraft show that long-term increases (of at least a factor of 2 near the surface) in tropospheric ozone have occurred over the past several decades, at least over the European continent. A very similar trend is seen at the West Coast of North America, at least beginning in the 1980s. These trends exhibit similar seasonal dependences, but the absolute ozone concentrations have significant latitudinal and regional dependencies. Two modeling studies (the RETRO program and a GEOS-Chem model simulation) designed to reproduce the evolution of the troposphere in response to emission changes over the past decades do not reproduce the observed trend for either continent over the modeling periods. Hence, the cause of the increasing ozone concentrations remains uncertain, indicating that a major feature of tropospheric composition is not understood.
A11F-06 INVITED
Modeling the Changing Chemical Composition of the Atmosphere: Impacts from the Stratosphere, Transport Modes and Climate Variability
The chemical composition of the atmosphere is permanently changing, driven by changes in emissions (natural and anthropogenic) as well as natural climate variability (e.g. El Nino, stratospheric variability). Here, an ensemble climate chemistry simulation for the period 1960 to 2020 is presented in which stratospheric and tropospheric chemistry are regarded consistently (Dameris et al., 2005; Grewe, 2007). Changes in chemistry and radiative forcing are analysed in detail. The results show: