TF HTAP Update and Upcoming Meetings

Contributors to the Task Force on Hemispheric Transport of Air Pollution (TF HTAP):

The three intersecting sets of experiments that comprise HTAP3 (OPNS, Fires, and MCHgMAP) are beginning to take shape and we welcome your participation in planning and implementing this work. Updates on each of these efforts are described below, along with links to register for or help plan upcoming meetings. 

Ozone, Particles, Nitrogen, and Sulfur deposition (OPNS)

A primary focus of this effort will be on informing the revision of the LRTAP Convention’s Gothenburg Protocol, including consideration of measures to address methane as a tropospheric ozone precursor.  Another objective will be to provide input to the WMO Measurement Model Fusion-Global Total Atmospheric Deposition (MMF-GTAD) project.

We will be asking for three types of simulations in this effort:

  1. Baseline and perturbation simulations with specified dynamics for a historical reference period (TBD) using the HTAPv3 global mosaic emission inventory. These experiments will be similar to those which many of you may remember from the HTAP phase 2 effort about 10 years ago. These experiments will be used to construct source-receptor relationships for an ensemble emulator which will be used for rapid assessment of future air pollutant emission scenarios.
  2. Specified dynamics simulations for the period 2000-2018 using the HTAPv3 emissions with comprehensive deposition fields as output. These experiments will support the WMO MMF-GTAD project.
  3. Transient free-running coupled chemistry-climate simulations with fixed SSTs based on SSP2-4.5 using CMIP6-like model configurations out to 2050 using a new set of air pollutant emission scenarios from the GAINS model developed to inform the upcoming revision of the CLRTAP Gothenburg Protocol. As well as being a general check on the ensemble emulator constructed from the specified dynamics simulations, this set of coupled runs will also serve specifically to examine the impact of various methane emission scenarios on future air quality.

We are currently working on a detailed concept document for these simulations which we hope to be able to share with the community by mid-November of this year for further discussion. We anticipate that simulations should be able to start in the northern Spring of 2024, with results delivered through 2025.

We invite interested members of the community to join us for online discussions of these model experiments in the week of November 27, 2023. We are planning two online meetings in this week: one for discussion of the specified dynamics simulations; and another for discussion of the coupled chemistry-climate runs. The meetings will each begin at 14:00 UTC and last two hours.

Link to the poll for discussion of the specified dynamics simulations:

Link to the poll for discussion of the chemistry-climate simulations:

We will circulate a more detailed concept document in advance of these meetings as a basis for discussion. We hope to see many of you then!

Multi-Model, Multi-Pollutant Modeling Study of Fire Impacts (Fires)

This set of experiments is focused on the impacts of wildfires and agricultural burning on fine particles, ozone, mercury, persistent organic pollutants, and other pollutants of concern.  The objective of the experiments is not only to learn about the various long-range transport impacts of fires, but learn from the effort to bring together different types of models to look across the full range of pollutants associated with fires. 

An options paper is being drafted and is open to contributions from the community  The effort is being led by Cyndi Whaley (  A separate email list serve has been set up for this project and you may subscribe at:

As part of this effort, TF HTAP is co-hosting a Fire Emissions Workshop with the IGAC/BBurned project to bring together the developers of major global fire emissions datasets to understand their methods and recent updates, discuss current intercomparison results and inventory disagreements, and determine which combination of fire emissions data would be useful for the HTAP3/Fires modelling study.

Fire Emissions Workshop

November 7,8,9 and 14, 2023

Register at:

We encourage all to attend!

Multi-Compartment Mercury Modeling and Analysis Project (MCHgMAP)

Work has already begun on preparing common input data sets for this set of experiments focused on simulating time series and process/source attribution for mercury.  This effort is initially focused on informing the effectiveness evaluation of the Minamata Convention on Mercury and the LRTAP Convention’s Heavy Metals Protocol.  MCHgMAP is being led by Ashu Dastoor (  An overview paper has been drafted and is being prepared for publication.  Much of the initial phase of modelling is expected to be completed in 2024, but the schedule will be refined in November after the Minamata Convention’s 5th Conference of the Parties. 

Thank you all for your continued interest and participation in the work of the TF HTAP.  Please let us know if you have any questions or suggestions.

Terry, Tim, Jacek, and RosaThe TF HTAP Leadership Team