A multi-model analysis of vertical ozone profiles

Abstract

A multi-model study of the long-range transport of ozone and its precursors from major anthropogenic source regions was coordinated by the Task Force on Hemispheric Transport of Air Pollution (TF HTAP) under the Convention on Long-range Transboundary Air Pollution (LRTAP). Vertical profiles of ozone at 12-h intervals from 2001 are available from twelve of the models contributing to this study and are compared here with observed profiles from ozonesondes. The contributions from each major source region are analysed for selected sondes, and this analysis is supplemented by retroplume calculations using the FLEXPART Lagrangian particle dispersion model to provide insight into the origin of ozone transport events and the cause of differences between the models and observations. <br><br> In the boundary layer ozone levels are in general strongly affected by regional sources and sinks. With a considerably longer lifetime in the free troposphere, ozone here is to a much larger extent affected by processes on a larger scale such as intercontinental transport and exchange with the stratosphere. Such individual events are difficult to trace over several days or weeks of transport. This may explain why statistical relationships between models and ozonesonde measurements are far less satisfactory than shown in previous studies for surface measurements at all seasons. The lowest bias between model-calculated ozone profiles and the ozonesonde measurements is seen in the winter and autumn months. Following the increase in photochemical activity in the spring and summer months, the spread in model results increases, and the agreement between ozonesonde measurements and the individual models deteriorates further. <br><br> At selected sites calculated contributions to ozone levels in the free troposphere from intercontinental transport are shown. Intercontinental transport is identified based on differences in model calculations with unperturbed emissions and emissions reduced by 20% by region. Intercontinental transport of ozone is finally determined based on differences in model ensemble calculations. With emissions perturbed by 20% per region, calculated intercontinental contributions to ozone in the free troposphere range from less than 1 ppb to 3 ppb, with small contributions in winter. The results are corroborated by the retroplume calculations. At several locations the seasonal contributions to ozone in the free troposphere from intercontinental transport differ from what was shown earlier at the surface using the same dataset. The large spread in model results points to a need of further evaluation of the chemical and physical processes in order to improve the credibility of global model results

North American isoprene influence on intercontinental ozone pollution

“…Most pertinent to our study is the model overestimate of summertime surface O 3 over the eastern United States; this is pervasive across the current generation of CTMs Reidmiller et al, 2009) and investigations into its cause are ongoing. Although we do not yet understand the source(s) of this bias in surface O 3 , the lack of a simple relationship between model biases with respect to the observations and the simulated O 3 responses to either domestic or intercontinental emission changes (Reidmiller et al, 2009;Jonson et al, 2010) suggests that additional tests are needed to evaluate the capability of models to adequately resolve the key processes governing intercontinental O 3 pollution. Comparison with monthly mean PAN measured at mountain sites (2-4 km altitude) in western NA (Mt.…”

“…The MOZART-2 SR1 simulation, which has previously been evaluated with observations of surface O 3 and O 3 profiles as part of the TF HTAP effort SR1 but with an isoprene nitrate recycling rate of 100% (up from 40% in SR1) SR6NA r100 SR6NA but with an isoprene nitrate recycling rate of 100% Reidmiller et al, 2009;Jonson et al, 2010), generally captures observed distributions and seasonality over most regions. Notable exceptions include systematic high biases of 10-20 ppb in summertime surface O 3 over the eastern United States and Japan, and systematic low biases of ∼15 ppb at mountainous sites in the western US and Europe and at lowaltitude sites in the northeastern US and central Europe during winter.…”

“…Intended to inform future policy negotiations under the Convention on Long-Range Transboundary Air Pollution (CLR-TAP), work to date has largely focused on "source-receptor" (SR) relationships (i.e., the pollutant response in a receptor region to an emissions perturbation within a source region) for anthropogenic emissions (TFHTAP, 2007;Shindell et al, 2008;Fiore et al, 2009;Reidmiller et al, 2009;Jonson et al, 2010;Anenberg et al, 2009). In regions heavily vegetated with isoprene-emitting plants, however, anthropogenic emissions of nitrogen oxides (NO x ) interact with isoprene, a highly reactive nonmethane volatile organic compound (NMVOC), to produce ozone (O 3 ) and thereby contribute to urban and regional air pollution (e.g., Trainer et al, 1987;Chameides et al, 1988).…”

Tropospheric Ozone Assessment Report: Assessment of global-scale model performance for global and regional ozone distributions, variability, and trends

“…Many of these models were biased low by about 10-30% in comparison to aircraft observations in the region (Monks et al, 2014) with biases in ozone precursors aligning with ozone biases . Similarly, evaluation of HTAP CTMs against high temporal frequency ozone vertical profiles at sites influenced by intercontinental transport of ozone and its precursors revealed model deficiencies (Jonson et al, 2010).…”

Aircraft-based observations and high-resolution simulations of an Icelandic dust storm

“…We present the results showing a footprint "Potential Emission Sensitivity" (PES) which represents the sensitivity of the measured air mass to global emissions backward in time for the lowest 100 m above the surface. Since most emissions occur at the surface, the footprint PES is of particular importance (Jonson, 2010).…”