Air quality HTAP

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AeroCom working group Air-Quality and HTAP cooperation

Participants for analysis


AeroCom model experiments for HTAP

As discussed during the 5th AeroCom workshop in Virginia Beach, October 2006, one of the activities in the second phase of AeroCom is to participate in the internationally coordinated multi-model studies of the Hemispheric Transport of Atmospheric Pollutants (HTAP). For background information, overview, and comprehensive description of the initial model experiments please go to Here we focus on the sub-sets of experiments that are particularly relevant to the AeroCom models in addressing the issues of long-range transport of particulate matters (PM) and their impact on regional air quality.

1. Planned model experiments

FIRST SET OF HTAP EXPERIMENTS: The initial HTAP experiments, set up in coordination with AeroCom, consist of two source-receptor experiments, SR1 (base run) and SR6 (perturbation run with 20% anthropogenic emissions in defined regions), and, as recommended addition one tracer experiment, TP1 (CO tracer). These experiments are described at the HTAP website. Registration is urgent and the experiments SR6 are expected for mid January. See for requirements AeroCom suggests that biomass burning and wild fire emissions are not considered as anthropogenic for the purpose of setting up experiment SR6.

Planned AeroCom experiments for HTAP

SR1 Base case simulation for year 2001. Each model uses own “best estimated” anthropogenic and natural emissions. Reference/verification

SR6_EA, SR6_SA, SR6_EU, SR6_NA Reducing anthropogenic emissions of SO2, BC, POM (and other aerosol precursors such as NOx, VOC, NH3 if capable) by 20% for regions East Asia (EA), Europe (EU), North America (NA), and South Asia (SA) Analyzing the effects of limiting oxidant effects on sulfate formation and transport; significance of emission reduction

SR6z_EA, SR6z_SA, SR6z_EU, SR6z_NA No anthropogenic emissions in EA, EU, NA, and SA Analyzing maximum impact of long-range transport

SR6d_AF, SR6d_ME, SR6d_AS No dust emissions in Africa (AF), Middle East (ME), and Asia (AS) Assessing maximum impact of long-range transport of dust

SR6b_ASB SR6b_NAB No biomass burning emissions in boreal Asia, and boreal North America Assessing maximum impact of long-range transport of biomass burning aerosol

TP1 CO tracer experiment using common surface sources, simple parameterization for chemical sources from CH4 and NMVOC, 25-day global lifetime (see HTAP document). Characterizing model transport

2. General guidelines

All model simulations shall be performed for the whole year 2001 with 6-month spin-up time. Meteorological data used in the model should be consistent with the 2001 condition. Models should have a horizontal resolution no coarser than 4x5 and at least 10 layers between surface and 30 hPa, covering at least the Northern Hemisphere.

2.1. Region definitions:

HTAP defines four regions that are of similar size and emission totals (Table 2a):

Table 2a. Anthropogenic source regions.

Name Region Longitude Latitude

EA East Asia 95E – 160E 15N – 50N

SA South Asia 50E – 95E 5N – 35N

EU Europe + North Africa 10W – 50E 25N – 65N

NA North America 125W – 60W 15N – 55N

AeroCom defines three dust regions and three wild fire regions in NH (Table 2b,2c):

Table 2b. Dust source regions.

Name Region Longitude Latitude

AS Asia 75E – 135E 30N – 50N

ME Middle East 40E – 75E 10N – 50N

AF Africa 20W – 40E 10N – 36N

Table 2c. Biomass burning source regions.

Name Region Longitude Latitude

ASB Boreal Asia 50E – 180E 45N – 70N

NAB Boreal North America 180W – 50W 45N – 70N

2.2. Standard diagnostics:

To obtain maximum logistic synergy between HTAP and AeroCom it is requested for all these experiments to follow the formatting and diagnostic specifications which are to be found and updated on the HTAP website ( (file names, explanations, links to tools)

The reference for which variables should be reported is to be found in the excel file, which is accessible via the HTAP website ( Please note that for the netCDF files both the variable names and the attribute standard_name are prescribed. See below the output files requested for the aerosol analysis part of HTAP/AeroCom experiments. The excel file contains also info on which variable belongs into which file.

For the aerosol part just one file per file category and year of simulation and experiment is requested. It is highly recommended to try to use the CMOR formatting package. Note that the additional experiments are not yet mentioned on the HTAP website and are not included in the HTAP tables for the CMOR formatting package.

3. Detailed description of experiments

3.1. Experiment SR1 – base run

The SR1 experiment is to establish a reference against the perturbation runs (SR6). The output of SR1 will be used to evaluate the models with observations and to verify the emission data. All models will be run in their own configurations with their preferred emission data sets for the conditions of 2001 (or a close year). Details are listed in Table 4.

Table 3. Analysis tasks and output definition for experiment SR1.

Task no. Task Output files Output frequency

SR1.1 Establish the mean model concentrations, check consistency of model output and compare with literature aerosolm metm emim depm budgetm monthly

SR1.2 Evaluate surface concentrations sfc daily

SR1.3 Evaluate aerosol mass and AOD distributions aerosolm aerosolaod monthly (aod=daily)

SR1.4 Evaluate budgets, and depositions depm budgetm monthly

3.2. Experiment SR6 – perturbation run

The SR6 experiments is to evaluate the effects of anthropogenic emission reduction in a particular region on surface air quality in all regions. The experiment should be performed the same as SR1, except that the anthropogenic emissions in a particular region (EA, SA, EU, NA) should be reduced uniformly by 20%. Only one region is perturbed at one time.

In addition to the HTAP defined experiments, AeroCom recommends three source-receptor experiments to assess the maximum impact of pollution and dust transport: SR6z, in which the anthropogenic emissions in the four specified regions are turned off; SR6d, in which the dust emissions in three major source regions are turned off; SR6b, in which wild fires are turned off.

Table 4. Analysis tasks and output definition for the three experiments in SR6.

Task no. Task Output files Output frequency

SR6.1 Evaluate the response of global and regional aerosol burdens to changes of anthropogenic aerosol and precursor emissions in specific regions (EA, SA, EU, NA) aerosolm budgetm emim depm Monthly

SR6.2 Evaluate the change in surface PM1, PM2.5, PM10 and aerosol species concentrations in response to changes of anthropogenic emission in specific regions sfc Daily Monthly

SR6.3 Evaluate regional contributions to PM and AOD aerosolm aerosolaod monthly (aod=daily)

SR6z.1 Evaluate maximum contributions of PM and AOD from regional emission and hemispheric transport from other regions (EA, SA, EU, NA) aerosolm aerosolaod Monthly Daily

SR6z.2 Evaluate deposition of PM from own regional emissions and hemispheric transport depm Monthly

SR6d.1 Evaluate maximum contributions of dust from major dust source regions (AS, ME, AF) to the PM and AOD in NH aerosolm emim Monthly

SR6d.2 Evaluate deposition of dust emitted from major source regions to other regions and to the ocean depm Monthly

SR6b.1 Evaluate maximum contributions of biomass burning aerosols from each Northern Hemisphere continent to PM and AOD aerosolm aerosolaod Monthly aod=daily

SR6b.2 Evaluate pathways of biomass burning aerosol from different continents (Arctic, local, circumpolar) Depm, aerosolm Monthly

3.3. Experiment TP1 – base and perturbation run (option)

Description of model set-up: A simple passive tracer with prescribed surface emissions (CO_direct) and a fixed, globally uniform lifetime of 25 days shall be introduced into the model. Surface emissions and common parameterizations shall be adopted from the common data sets provided on the HTAP website. Four additional tracers shall be defined to label “CO” from sources in East Asia, South Asia, Europe, and North America (CO_EA, CO_SA, CO_EU, and CO_NA). Where possible, another five additional tracers to simulate anthropogenic and biogenic NMVOC emissions (aVOC and bVOC) and the CO produced from their oxidation (CO_aVOC, CO_bVOC) and from the oxidation of methane (CO_CH4) should also be defined. A sample FORTRAN subroutine implementing this set-up into the ECHAM model will be provided on the HTAP web pages. If not all tracers can be defined in your model, we ask you to at least participate in this experiment with the simulation of the global CO tracer from direct emissions.

Table 5. Analysis tasks and output definition for experiments in TP1.

Task no. Task Output files Output frequency

TP1.1 Evaluate the global CO distribution from direct CO emissions in specific regions (EA, EU, NA, SA) tracem Monthly

TP1.2 Evaluate the source-receptor relationships for regional CO emissions in specific regions (EA, EU, NA, SA) tracem Monthly

TP1.3 Evaluate the regional contributions of the different chemical sources to the CO burden tracem Monthly

ADDITIONAL SET OF HTAP-AEROCOM EXPERIMENTS: In addition to the HTAP defined runs, AeroCom recommends three more perturbation runs. The first one is SR6z, in which anthropogenic emissions in specified pollution regions are turned off, put to zero, in order to assess the maximum impact of hemispheric transport of aerosols on regional air quality. (Note: a 20% reduction of anthropogenic emission specified in HTAP is most appropriate for ozone runs since the highly non-linear chemistry in ozone production would make the results from zeroing-out emission runs difficult to interpret.) AeroCom again suggests that biomass burning and wild fire emissions are not considered as anthropogenic for the purpose of setting up experiment SR6z.

The second one is SR6d, in which the dust emissions from major dust source region are turned off in order to estimate the impact of long-range transport of dust from a particular source region on air quality over land and on eco- system. Given the fact that long-range transport of dust is the most important mechanism for aerosol transport and the most visible from satellite data, this experiment is particularly relevant to HTAP even though most dust is from natural sources.

The third experiment is SR6b, in which emissions due to wild fires and biomass burning in the Northern Hemisphere are set to zero in three regions. The purpose of this experiment is to establish the contribution to background aerosol levels from natural and anthropogenic wild fires. Fire produced aerosols have particular potential of being long range transported.

We suggest as a deadline for submitting the additional experiments the 15th of April. Table 1 summarizes all experiments (high-lighted are the additional experiments). For the purpose of HTAP study, anthropogenic emissions are defined as all fossil and biofuel combustion, industrial, residential/commercial activities (including aircraft and shipping emissions), and agriculture activities. Wild fire and biomass burning emissions should at best correspond to the actual fire situation in the year of simulation. Note that modelers are encouraged to use the emissions of their choice.