The effect of pyro-convective fires on the global troposphere: comparison of TOMCAT modelled fields with observations from ICARTT Sarah Monks Outline: Brief introduction to the relevance of the work done Discuss the effect of forest fires on the troposphere Present some of the results from comparing the global chemical transport model to observations

Introduction Over recent years it has become accepted that emissions from one region can be easily transported to another Intercontinental transport can affect regional air quality The International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) 2004 took place over the Atlantic  Gain a better understanding of: - Regional air quality - Intercontinental transport of Ozone and it’s precursors O 3 is formed photochemically from NMHC and CO in the presence of NO X. Ozone (O 3 ) is an important trace gas:  It is a greenhouse gas  Its distribution affects the oxidising capacity of the troposphere  It is harmful to living organisms

Biomass Burning in Alaska, 2004 Extensive forest fires in Alaska in 2004 during ICARTT Forest fires emit a wide variety of reactive trace gases into the atmosphere including: -CO, hydrocarbons and NO X (=NO + NO 2 ) In the summer of 2004 the Alaskan forest fire emissions dominated the distributions of trace species over the Atlantic Pyro-convection lifts the trace species up to the free troposphere – effect global troposphere

Projects Aims Test whether a global chemical transport model (CTM) can reproduce ICARTT in situ observations of trace species  The effect of model resolution  The effect of convection and vertical diffusion  Comparison of Eulerian and Lagrangian models (see poster)  Test TOMCAT’s treatment of mixing and chemistry (see poster) Quantify the impact of the forest fires

TOMCAT MODEL Eulerian 3D global chemical transport model (CTM) Forced by meteorological analyses from ECMWF 31 vertical levels (1000 hPa – 10 hPa) Variable horizontal resolution: used 5.6° x 5.6° and 2.8° x 2.8° Chemistry scheme: 41 chemical species, 118 chemical reactions Subgrid-scale processes: convection and vertical diffusion are parameterised

Observations ICARTT Aircraft measurements: - CO, O 3, C 2 H 6, C 3 H 8 DC8 BAe-146 Falcon MOPITT satellite instrument: - CO observations

Additional Alaskan Forest fire emissions Initial full chemistry simulations:  Emission region: E and – 66.5N  Mixing up to ~250hPa to simulate pyro-convection  Emitted at a constant rate from 15 th July 2004 to end of August Sensitivity simulation:  Emission region extended to: – 239E and 61 – 67N  Mixing reduced to ~350 hPa  Increased surface fluxes to represent increased emission rate Trace Species Mass flux in initial runs (Tg) Mass flux in sensitivity run (Tg) CO NO X C2H6C2H C3H8C3H

Impact of Forest Fires on CO Control Run:  No forest fire emissions With Alaskan forest fires:  Large increase in CO – greater than US anthropogenic emissions  33% increase in CO plume over the Atlantic MOPITT CO total column:  Plume of CO over Canada and Atlantic observed in the same location

Comparisons to ICARTT Data More detailed comparisons to in situ observations from ICARTT Model can reproduce CO vertical profiles on days when the aircraft did not target fire plumes Model is unable to capture the magnitude forest fire enhancements on the 18 th, 20 th and 23 rd July  Extensive vertical mixing on the 23rd resulting in a nearly uniform concentration throughout the troposphere

Ethane and Propane Model cannot reproduce magnitude of enhancements in forest fire plumes The peak in propane is underestimated by a factor of 2.6 whereas ethane is only underestimated by a factor of 1.2  Suggests the 0.08 Tg of propane emitted from Alaska is not sufficient

Emission Region 20 th July 2004 at 500 hPa (with Alaskan forest fires): There is a plume to the North of the BAe-146 flight region with concentrations of up to 230 ppbv of CO and1800 pptv of ethane In July the forest fires moved more to the east The emissions will have been subjected to different meteorological conditions This caused the plume sampled by the aircraft on the 18 th and 20 th to be displaced in the model

Modelled Pyro-Convection 20 th July 2004 at 350 hPa (with Alaskan forest fires): Concentrations over Alaska are much too high (greater than 200 ppbv) Mixing scheme which is simulating pyro-convection is too strong This will lift too much CO up and therefore TOMCAT will underestimate CO at lower levels

Switching off Convection North America Over the US convection and vertical diffusion are needed to prevent a build up of pollution in the boundary layer Demonstrates the importance of including a convection scheme in a model Atlantic and Europe Greatly improves the gradients of some of the profiles over the Atlantic and Europe

Changes to Alaskan Forest Fires Emissions Total CO column: 44% increase in CO in the plume over the Atlantic CO is still underestimated by 13% in this region CO concentration on the 20 th July at 500 hPa: Extending the emission region moves the plume closer to the flight track CO in the plume increases from 230 ppbv to 245 ppbv

Forest Fires Impact on the O 3 Burden 18th July at 400 hPa: -31% increase in ozone -Concentrations of ppbv 20th July at 500 hPa: -Ozone increases by 47 % -concentrations of up to 78 ppbv. The tracer fields show the displaced plumes. The concentrations of these plumes are better matches to the observed O3 at these altitudes.

Contribution of forest fires to ozone burden: The largest impact on the ozone budget can be seen in the emission region, where the contribution to ozone is greater than 15 ppbv Ozone is perturbed by 1ppbv throughout the whole Northern Hemisphere Forest Fires Impact Regional Air Quality Over Europe The fires contribute 1-2 ppbv The largest impact from the fires in Europe can be seen over the UK, with up to 4 ppbv contributed from the fires

Summary The model can reproduce observed CO and O 3 on days when the aircraft did not target fire plumes The performance of the model was shown to be very sensitive to the chosen emission region Parameterised convection and vertical diffusion are needed in a CTM, however, they were overly strong on certain days Alaskan forest fires contributed a large quantity of trace species to the global troposphere which will effect tropospheric chemistry The forest fires affected regional air quality as far as Europe with up to a 4 ppbv contribution over the UK.