HTAP 2020 workshop summary

These summaries are organised around the session topics from the workshop and based on the feedback received via the Google form and discussions and presentations given during the workshop. Throughout this summary, numbers provided in { } refer to items in the LRTAP Convention’s 2020-2021 work plan. This workshop is {1.1.4.7} and contributes to {2.1.3}.

Policy-Relevant Questions from the LRTAP Convention

The Task Force welcomed a presentation by the WGSR vice chair that identified current priorities for policy development within the Convention and an initial set of policy-relevant questions from the WGSR bureau that could be addressed by TF HTAP. A number of the questions can be answered in whole or in part by analyses that have already been completed. Other questions will require further analyses by TF HTAP or other groups under the Convention. In some cases, additional long term research may be necessary. The Task Force chairs will provide feedback to the WGSR bureau and will initiate an online document to facilitate a dialogue and engage the broader Task Force in formulating answers to the policy-relevant science questions.

Participants expressed strong interest in contributing to 6 of the activities proposed by the chairs at the start of the meeting. In order of interest:

  • Assessment of the benefits of methane mitigation {1.1.4.4}
  • Analysis of trends to inform the review of the Gothenburg Protocol {1.1.3.2}
  • Assessment of the benefits of shipping mitigation {1.1.4.4}
  • Comparison of source/receptor methods
  • Development of openFASST {1.1.4.6}
  • Development of the HTAPv3 emissions mosaic {1.1.4.5}

A number of participants also expressed continued interest in global and regional model evaluation (and process diagnostics), which is a long-term interest for TF HTAP.

This interest from the community will help to steer the implementation of the TF HTAP work plan.

Ozone and Methane: Scenarios and Mitigatio

Many of the responses to this theme overlapped with the theme “Ozone and methane: emissions and atmospheric response”. These are considered below.

Several other groups are working on scenarios or identification of measures for methane mitigation and tools for assessing impacts (e.g. CIAM (IIASA), TFTEI, JRC, USEPA, CCAC). TF HTAP will continue to monitor activities from these groups, and coordinate with TFIAM to produce a synthesis of the results {1.1.4.4}.

HTAPv3 Emissions Mosaic

The relevance and usefulness of a new mosaic inventory was reaffirmed during the workshop. Participants agreed with the TF HTAP chairs that detailed sectoral resolution and multi-year trends will be important aspects of the inventory. Spatial and sub-annual temporal resolution was also
identified by participants as important. The development process of the mosaic inventory could be a useful opportunity to provide feedback to providers of regional data. Initial discussions regarding the development of the inventory have already started and will continue with high priority {1.1.4.5}. The mosaic is to be completed in the next two years (near term) and will be available for simulations in the longer term.

Links to Ozone Observational Analyses

TOAR2 data will be very useful for evaluation of HTAP models. The Task Force discussed the potential for a working group to identify metrics to serve as benchmarks for ozone model evaluation. The working group may involve experts associated with WMO, CCMI, TF HTAP, TFMM, AQMEII, and MICS. Over the long term, observational benchmarks may be used to weight individual models in future HTAP ensembles, as demonstrated by some of the analyses used to support the Global Burden of Disease study.

Output from HTAP models may be useful for MMF-GTAD. There are already strong synergies between AQMEII4 and MMF-GTAD and TF HTAP should look to how our participants can engage and support these activities, as opposed to initiating separate work.

Ozone and Methane: Emissions and Atmospheric Response

There is a lot of work being done by both the forward and inverse modelling communities on this topic. Methane contributes significantly to global background surface ozone, but the regional response is also influenced by local emissions, especially NOx. Large inter-model uncertainty in global OH leads to a wide range of methane emissions in concentration-driven simulations (both inverse studies and “standard” configurations of most CCMs and CTMs). Emission-driven simulations are not frequently performed; to date, simulated methane concentrations from emission-driven simulations differ significantly from observations. Large inter-model differences in methane lifetime also likely leads to large differences in the modelled ozone responses to methane, but this has not been well explored.

A large amount of existing data (e.g. GAW observations) is already available from model inter-comparison projects such as AerChemMIP. These datasets should be more fully explored and evaluated before any further model inter-comparisons are planned to address this topic.

In the near term, TF HTAP should focus on exploring parameterizations of the results of existing simulations, including HTAP2, the UNEP/CCAC Global Methane Assessment, and AerChemMIP. These parameterizations can be used to characterize the magnitude and uncertainty in the ozone response to methane mitigation.

Over the longer term, TF HTAP could explore the reasons for the large inter-model differences in OH and methane lifetime through model intercomparisons and analyses of OH and O3 budgets. A reasonable first step might be the development of a scoping paper.

Ozone Impacts on Vegetation

Modelling ozone impacts on vegetation is complex. TF HTAP should improve coordination between its efforts and the work of the vegetation impact modelling experts within the convention (especially ICP Vegetation and EMEP MSC-W). The atmospheric model output requirements of impact
assessment modellers should be considered in any future HTAP model inter-comparison exercises. Ozone deposition to vegetation is also an important loss process for atmospheric ozone which is poorly represented in most HTAP models. Improvement of model deposition schemes could improve the quality of data provided to impact modellers while also improving ozone in simulations.

In the near term, it could be useful to build on the work done by AQMEII4 and MMF-GTAD in understanding the range of deposition and land cover schemes used in HTAP models. Global HTAP models may also be able to perform some of experiments defined by AQMEII4 (e.g. the box model experiments) that would enable global and regional model intercomparisons.

Ozone Impacts on Human Health

The methods and tools for estimating the human health impacts of air quality results from HTAP simulations are well established (at least for some health endpoints), although dose/response relationships continue to evolve with further research. It is important that TF HTAP’s analyses of S/R relationships be performed with the metrics that are being used for human health (and ecosystem health) assessment, which may be different from metrics articulated in policy objectives or ambient standards.

Links to Other Model Inter-comparisons

Within the LRTAP Convention, the TFMM Eurodelta exercise can potentially overlap with HTAP activities. The Eurodelta trends multi-model inter-comparison included attribution of ozone trends to emission trends within Europe and hemispheric transport. Ozone output in these runs remains under-analysed. Future HTAP activities on ozone trends in Europe should consider making use of Eurodelta trends. Current multi-model TFMM activities are focused on carbonaceous aerosol. In the longer-term, TF HTAP and TFMM could coordinate activities on global-to-regional ozone modelling.

There is a very large amount of data available from the AerChemMIP global model inter-comparison, and there are also simulations available from the AMAP Expert Group on SLCF. TF HTAP participants could be encouraged to contribute CTM results to specific AerChemMIP, AMAP SLCF, WGNE/S2S/APP and PREFIA experiments for purposes of comparison.

Before TF HTAP starts any new multi-model exercises, it should make sure that any relevant analysis has already been attempted with data from HTAP2, AerChemMIP, AMAP, or others. Analysis of the methane-ozone link in the AerChemMIP runs is especially promising. Future HTAP perturbation studies could be based on AerChemMIP runs. TF HTAP should also stay informed about phase 2 of CCMI and GAFIS due to the large overlap in the communities.

The AQMEII4 regional multi-model exercise is currently focused on inter-comparison of deposition processes. TF HTAP should monitor the results of this work with regard to deposition of ozone.

The primary mode of collaboration with the MICS-Asia project is likely through harmonisation of emission inventories (contributing to the HTAPv3 mosaic inventory).

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