Particulate matter in GEOS-Chem: Difference between revisions

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On this page we provide information about how to compute particulate matter concentrations from GEOS-Chem output.
On this page we provide information about how to compute particulate matter concentrations from GEOS-Chem output.


== Definition ==
== Definitions of PM2.5 and PM10 for GEOS-Chem ==


'''''[http://fizz.phys.dal.ca/~rvmartin/ Randall Martin] wrote, with contributions from Daven Henze, Aaron van Donkelaar, and Jeff Pierce:'''''
=== PM2.5 definition ===


:The PM2.5 calculation should account for aerosol water of PM2.5 in a way that is consistent with the PM2.5 measurements.  The water content of PM2.5 is operationally defined.  In the United States an RH of 35% is [https://www3.epa.gov/ttnamti1/files/ambient/pm25/spec/drispec.pdf often used] and would be appropriate for the benchmark.  In Europe an RH of 50% is often used.
Below is the definition of PM2.5 used in GEOS-Chem and approved by the [[Aerosols Working Group]].  


:Below are the factors that account for aerosol water in a consistent manner as used in jv_spec.dat from GC v10-01-01, as calculated by Aaron van Donkelaar and Sajeev Philip.
This table lists hygroscopic growth factors for PM2.5 constituent species:


:At 35% RH:
{| border=1 cellspacing=0 cellpadding=5
::1.33 for SO4, NIT, and NH4
|-valign="top" bgcolor="#cccccc"
::1.16 for OCPI and SOA
!width="120px"|Scale factor
::1.86 for SALA
!width="200px"|Multiplies these species
!width="120px"|Value at 35% RH
!width="120px"|Value at 50% RH


:At 50% RH the values are
|-valign="top" align="center"
::1.51 for SO4, NIT, and NH4
|SIA_GROWTH
::1.24 for OCPI and SOA
|SO4, NIT, NH4
::2.42 for SALA
|1.10
|1.35


:These growth factors are calculated using the change in radius between different RH within jv_spec.dat.  Essentially, the change in radius between the dry (i.e. 0% RH) and wet (35% or 50% RH) aerosol is treated as a shell of water for the purposes of calculating the additional mass associated with the wet particle. Under this condition, it can be shown that:
|-valign="top" align="center"
|ORG_GROWTH
|OCPI, SOA
|1.05
|1.07


::WetMass2DryMassRatio = 1 + [{(radiusAtRH_wet / radiusAtRH_dry)^3 - 1} x (Density_Water / Density_DrySpecies)]
|-valign="top" align="center"
|SSA_GROWTH
:The DST2 bin includes aerosols with diameter both smaller and larger than 2.5 um. Lengthy discussion with Duncan Fairlie, Aaron van Donkelaar, Colette Heald, Jeff Pierce and Noelle Selin led to the conclusion that 38% of the DST2 bin should be included in the calculation of PM2.5.
|SALA
|1.86
|1.86


:In summary, the PM2.5 benchmark and wiki documentation should be changed to
|}


  PM25    = 1.33 (NH4 + NIT  + SO4) + BCPI + BCPO + 2.1 (OCPO + 1.16 OCPI) + 1.16 SOA 
The OA changes at both RH, and the SIA change at 50% RH are straightforward changes to yield consistency between with the current Kappa-Kohler hygroscopicity parameterization in GEOS-Chem based on Latimer and Martin (2019).  
              + DST1 + 0.38 DST2 + 1.86 SALA


:where the tracer units in ug/m3 at STP, and the value of 2.1 is the global mean OM/OC as recommended by the [[Aerosols Working Group|Aerosol WG]].  
The SIA recommendation at 35% RH is less certain since it depends on the efflorescence RH of the SIA in the aerosol mixture under the variable conditions of the instruments, collection media, and laboratories involved. Given knowledge gaps about the aerosol phase at low RH, the proposed growth factor of 1.1 assumes that half of the particles are aqueous (growth factor of 1.19 for Kappa-Kohler) and the other half are crystalline (growth factor of unity).


--[[User:Melissa Payer|Melissa Sulprizio]] ([[User talk:Melissa Payer|talk]]) 13:19, 30 June 2016 (UTC)
These growth factors are calculated using the change in radius between different RH.  Essentially, the change in radius between the dry (i.e. 0% RH) and wet (35% or 50% RH) aerosol is treated as a shell of water for the purposes of calculating the additional mass associated with the wet particle.  Under this condition, it can be shown that:


=== Including SOA in PM2.5 ===
GrowthFactor = 1 + [{(radiusAtRH_wet / radiusAtRH_dry)^3 - 1} x (Density_Water / Density_DrySpecies)]


SOA should be defined to include all SOA tracers used in the benchmark. This will evolve as the Aerosol WG recommends new SOA options. At present, the best way to represent SOA is as   
Emissions from the Anthropogenic Fugitive, Combustion and Industrial Dust (AFCID) (cf [https://iopscience.iop.org/article/10.1088/1748-9326/aa65a4 Philip et al (2017)] are automatically added to the DST1 bin in most GEOS-Chem simulations.  AFCID is activated by default but can be disabled by the user if so desired.
*TSOA0, TSOA1, TSOA2, TSOA3 = Lumped semivolatile aerosol products of monoterpene + sesquiterpene ox.
*ISOA1, ISOA2, ISOA3, = Lumped semivolatile aerosol products of isoprene oxidation
*ASOAN, ASOA1, ASOA2, ASOA3 = Lumped nonvolatile aerosol products of light aromatics and IVOCs
The molecular weights are 150 g/mol for all above SOA tracers.


[[GEOS-Chem v11-02#v11-02c|GEOS-Chem v11-02c]], introduced several new SOA species that should be included in the PM2.5 definition.
The DST2 bin includes aerosols with diameter both smaller and larger than 2.5 um. Fangqun Yu has recently determined that [[APM_aerosol_microphysics#Dust_Particle_Size_Distribution|30% of DST2 should be included in PM2.5]].  (The prior value of 38%, which had been established by Duncan Fairlie, Aaron van Donkelaar, Colette Heald, Jeff Pierce and Noelle Selin, was used until [[GEOS-Chem 13.4.0]].)


For the [[Secondary_organic_aerosols#Complex_SOA_scheme|complex SOA scheme]]:
In summary, PM2.5 at 35% RH should be computed as:
*ISOAAQ = isoprene SOA from aqueous formation, includes
**SOAGX = Aerosol-phase glyoxal (58 g/mol)
**SOAMG = Aerosol-phase methylglyoxal (72 g/mol)
**SOAIE = Aerosol-phase isoprene epoxide (118 g/mol)
**SOAME = Aerosol-phase C4 epoxide from oxidation of PMN (102 g/mol)
**INDIOL = Generic aerosol-phase organonitrate hydrolysis product (102 g/mol)
**LVOCOA = Aerosol-phase low-volatility non-IEPOX product of ISOPOOH (RIP) oxidation (154 g/mol)
**ISN1OA = Aerosol-phase 2nd generation hydroxynitrates formed from ISOP+NO3 reaction pathway (226 g/mol)


For the [[Secondary_organic_aerosols#Simple_SOA_scheme|simple SOA scheme]]:
PM25 = ( NH4 + NIT  + SO4 ) * 1.10
*SOAS = Simple SOA (150 g/mol)
      + BCPI
      + BCPO
      + ( OCPO + ( OCPI * 1.05 ) ) * (OM/OC ratio)  # OM/OC ratio = 2.1 by default
      + DST1
      + DST2 * 0.30                                # F. Yu suggests 30% of DST2 (Nov 2011); prior value was 38% of DST2
      + SALA * 1.86
      + SOA  * 1.05


'''IMPORTANT:''' When using the complex SOA scheme, the Aerosols WG warns that the PM2.5 calculation in GEOS-Chem currently includes all the SOA formed in both the [http://www.atmos-chem-phys.net/10/11261/2010/acp-10-11261-2010.pdf Pye et al. (2010)] and [http://acmg.seas.harvard.edu/publications/2016/Marais_SEUS_isopSOA_ACP_2016.pdf Marais et al. (2016)] scheme and may include some double-counting of isoprene SOA.
By default, the OM/OC ratio is set to a constant value of 2.1. For users who seek more information on the seasonal and spatial variation of OM/OC in the lower troposphere, we provide the option to use the [http://fizz.phys.dal.ca/~atmos/martin/?page_id=2157 seasonal gridded dataset] developed by [http://www.sciencedirect.com/science/article/pii/S1352231013009151 Philip et al. (2014)]. This dataset has some uncertainty, but offers more information than a global-mean OM/OC ratio in regions where primary organic aerosols have a large fossil fuel source.


--[[User:Melissa Payer|Melissa Sulprizio]] ([[User talk:Melissa Payer|talk]]) 19:02, 8 September 2017 (UTC)
''NOTE: Some modifications to this basic definition are necessary, depending on the SOA species that are used in a given GEOS-Chem simulation.  See the [[#PM2.5 and PM10 diagnostics for GEOS-Chem|PM2.5 and PM10 diagnostics for GEOS-Chem]] section below for details.''


=== Option to include spatially and seasonally varying OM/OC ===
=== PM10 definition ===


<span style="color:green">'''''This update was included in [[GEOS-Chem v11-02#v11-02e|v11-02e]] (approved 24 Mar 2018).'''''</span>
In GEOS-Chem 13.4.0 and later versions, PM10 at 35% RH is computed according to the following formula:


For users who seek more information on the seasonal and spatial variation of OM/OC in the lower troposphere, we provide the option to use the [http://fizz.phys.dal.ca/~atmos/martin/?page_id=2157 seasonal gridded dataset] developed by [http://www.sciencedirect.com/science/article/pii/S1352231013009151 Philip et al. (2014)]. This dataset has some uncertainty, but offers more information than a global-mean OM/OC ratio in regions where primary organic aerosols have a large fossil fuel source.
PM10 = PM2.5
      + ( DST2 * 0.7  )
      + DST3
      + ( DST4 * 0.9  )
      + ( SALC * 1.86 )   # NOTE: The value of 1.86 is the SSA_GROWTH factor at 35% RH


--[[User:Melissa Payer|Melissa Sulprizio]] ([[User talk:Melissa Payer|talk]]) 16:33, 23 May 2017 (UTC)
The constant scale factors for DST2 (70%) and DST4 (90%) were determined by Fanqun Yu from [[APM aerosol microphysics]] simulations.  For more information, [[APM_aerosol_microphysics#Dust_Particle_Size_Distribution|please follow this link.]].


== PM2.5 in the 1-yr benchmark plots ==
''NOTE: Some modifications to this basic definition are necessary, depending on the SOA species that are used in a given GEOS-Chem simulation.  See the [[#PM2.5 and PM10 diagnostics for GEOS-Chem|PM2.5 and PM10 diagnostics for GEOS-Chem]] section below for details.''


=== GEOS-Chem v11-01 and later versions ===
== PM2.5 and PM10 diagnostics for GEOS-Chem ==


In [[GEOS-Chem v11-01]] the definition of PM2.5 was changed following the recommendation by Randall Martin and the Aerosol WG [[#Definition|as described above]]. The definition now used to create the plots for GEOS-Chem 1-year benchmark simulations is:
The PM2.5 and PM10 diagnostics belong to the [[History_collections_for_aerosols#The_AerosolMass_collection|the AerosolMass collection]] in the GEOS-Chem History diagnotics). They are computed according to the code below, which may be found in <tt>GeosCore/aerosol_mod.F90</tt>.


  ; Convert ppbv to ug/m3
        !==============================================================
  STP_P    = 1013.25
        ! P A R T I C U L A T E  M A T T E R
  STP_T    = 298.
        !
  ppb_ugm3 = 1e6 / 8.314 * 100. * STP_P/STP_T *1e-9
        ! See this GEOS-Chem wiki page for the most up-to-date
    
        ! definitions of PM2.5 and PM10 used in GEOS-Chem:
  MWaer    = [18, 12, 12, 62, 96, 29, 31.4] ; NH4, EC, OC, NIT, SO4, DUST, SALA
        !
        ! <nowiki>http://wiki.geos.chem.org/Particulate_Matter_in_GEOS-Chem</nowiki>
        !==============================================================
        ! Particulate matter < 2.5um [kg/m3]
        PM25(I,J,L) = NH4(I,J,L)        * SIA_GROWTH + &
                      NIT(I,J,L)        * SIA_GROWTH + &
                      SO4(I,J,L)        * SIA_GROWTH + &
                      BCPI(I,J,L)                    + &
                      BCPO(I,J,L)                    + &
                      OCPO(I,J,L)                    + &
                      OCPI(I,J,L)      * ORG_GROWTH + &
                      SALA(I,J,L)      * SSA_GROWTH + &
                      SOILDUST(I,J,L,1)              + &  ! + 100% of DST1
                      SOILDUST(I,J,L,2)              + &  !
                      SOILDUST(I,J,L,3)              + &  !
                      SOILDUST(I,J,L,4)              + &  !
                      SOILDUST(I,J,L,5) * 0.3_fp          ! + 30%  of DST2
   
        ! Particulate matter < 10um [kg/m3]
        PM10(I,J,L) = PM25(I,J,L) +                    &  ! PM2.5
                      SOILDUST(I,J,L,5) * 0.7_fp    + &  ! + 70%  of DST2
                      SOILDUST(I,J,L,6)              + &  ! + 100% of DST3
                      SOILDUST(I,J,L,7) * 0.9_fp    + &  ! + 90%  of DST4
                      SALC(I,J,L)      * SSA_GROWTH
        ! Include either simple SOA (default) or Complex SOA in
        ! PM2.5 calculation.  In simulations where both Simple SOA and
        ! Complex SOA species are carried (i.e. "benchmark"), then
        ! only the Simple SOA will be added to PM2.5, in order to avoid
        ! double-counting. (bmy, 5/11/18)
        IF ( Is_SimpleSOA ) THEN
          PM25(I,J,L) = PM25(I,J,L) + ( SOAS(I,J,L) * ORG_GROWTH )
          PM10(I,J,L) = PM10(I,J,L) + ( SOAS(I,J,L) * ORG_GROWTH )
        ELSE IF ( Is_ComplexSOA ) THEN
          PM25(I,J,L) = PM25(I,J,L)                + &
                        TSOA(I,J,L)  * ORG_GROWTH  + &
                        ASOA(I,J,L)   * ORG_GROWTH  + &
                        ISOAAQ(I,J,L) * ORG_GROWTH        ! Includes SOAGX
          PM10(I,J,L) = PM10(I,J,L)                + & 
                        TSOA(I,J,L)  * ORG_GROWTH  + &
                        ASOA(I,J,L)  * ORG_GROWTH  + &
                        ISOAAQ(I,J,L) * ORG_GROWTH        ! Includes SOAGX
   
   
  NH4_ugm3  = NH4( indlon, indlat, 0)*ppb_ugm3*MWaer(0)
          ! Need to add OPOA to PM2.5 for complexSOA_SVPOA simulations
  NIT_ugm3  = NIT( indlon, indlat, 0)*ppb_ugm3*MWaer(3)
          ! -- Maggie Marvin (15 Jul 2020)
  SO4_ugm3  = SO4( indlon, indlat, 0)*ppb_ugm3*MWaer(4)
          IF ( Is_OPOA ) THEN
  BCPI_ugm3 = BCi( indlon, indlat, 0)*ppb_ugm3*MWaer(1)
              PM25(I,J,L) = PM25(I,J,L) + ( OPOA(I,J,L) * ORG_GROWTH )
  OCPI_ugm3 = OCi( indlon, indlat, 0)*ppb_ugm3*MWaer(2)
              PM10(I,J,L) = PM10(I,J,L) + ( OPOA(I,J,L) * ORG_GROWTH )
  BCPO_ugm3 = BCo( indlon, indlat, 0)*ppb_ugm3*MWaer(1)
          ENDIF
  OCPO_ugm3 = OCo( indlon, indlat, 0)*ppb_ugm3*MWaer(2)
        ENDIF
  DST1_ugm3 = Dst1(indlon, indlat, 0)*ppb_ugm3*MWaer(5)
  DST2_ugm3 = Dst2(indlon, indlat, 0)*ppb_ugm3*MWaer(5)
  SALA_ugm3 = SALA(indlon, indlat, 0)*ppb_ugm3*MWaer(6)
   
   
  ; Compute PM2.5
        ! Apply STP correction factor based on ideal gas law
  PM25 = 1.33 * ( NH4_ugm3 + NIT_ugm3 + SO4_ugm3 ) + &
        PM25(I,J,L) = PM25(I,J,L) * ( 1013.25_fp / PMID(I,J,L) ) * &
          ( BCPI_ugm3 + BCPO_ugm3 ) + 2.1 * (1.16 * OCPI_ugm3 + OCPO_ugm3) + &
                                    ( T(I,J,L) / 298.0_fp    )
          1.16*SOA_ugm3 + DST1_ugm3 + (0.38 * DST2_ugm3) + (1.86 * SALA_ugm3)
 
where the tracer units are ug/m3 at STP, and the value of 2.1 is the global mean OM/OC as recommended by the Aerosol WG.
 
--[[User:Melissa Payer|Melissa Sulprizio]] ([[User talk:Melissa Payer|talk]]) 13:19, 30 June 2016 (UTC)
 
=== GEOS-Chem v10-01 and earlier versions ===
 
Here is the definition of PM2.5 that we use to create the plots for GEOS-Chem 1-year benchmark simulations:
 
  ; Convert ppbv to ug/m3
  STP_P    = 1013.25
  STP_T    = 298.
  ppb_ugm3 = 1e6 / 8.314 * 100. * STP_P/STP_T *1e-9
   
   
  ; Compute PM2.5
         PM10(I,J,L) = PM10(I,J,L) * ( 1013.25_fp / PMID(I,J,L) ) * &
  PM25    = ( ( NH4         )      * ppb_ugm3 * 18 )
                                    ( T(I,J,L)  / 298.0_fp    )
          + ( ( NIT        )       * ppb_ugm3 * 62 )
          + ( ( SO4        )       * ppb_ugm3 * 96 )
          + ( ( BCPI + BCPO )      * ppb_ugm3 * 12 )
          + ( ( OCPI + OCPO ) * 2.1 * ppb_ugm3 * 12 )
          + ( ( DST1 + DST2 )      * ppb_ugm3 * 29 )
 
Where NH4, NIT, SO4, BCPI, BCPO, OCPI, OCPO, NO3, DST1, and DST2 have units of ppbv.
 
We use the value 2.1 for OM:OC, but note from [[#Past discussions|Jeff Pierce's comment in the section above]] that this is an open question.
 
'''''[[User:Cheald|Colette Heald]] wrote:'''''


:For completeness PM2.5 should include accumulation mode sea salt (SSa), but that's not included in the PM2.5 calculations used in the benchmarks, I think just for historical reasons since the code was written for continental US sites. It may be worth adding this comment to the wiki for folks who are using this as a guideline for calculating PM2.5.
Also note that there are some calculations that were not included in the [[#Definitions of PM2.5 and PM10 for GEOS-Chem|basic definitions of PM2.5 and PM10 in the preceding sections]]. These are:


--[[User:Bmy|Bob Y.]] 17:11, 13 February 2015 (EST)
=== Avoid double-counting of ISOAAQ species ===


== PM2.5 diagnostic ==
[[User:jaf|Jenny Fisher]] rightly pointed out that the PM2.5 diagnostic [[Secondary_organic_aerosols#Only_add_ISOAAQ_species_to_PM2.5_diagnostics_for_simulations_using_the_complex_SOA_option|was erroneously including the ISOAAQ species in the accounting of PM2.5 when the Simple SOA option was used]].  After discussion with the [[Aerosols Working Group]], we modified the PM2.5 and PM10 diagnostic computations accordingly: 


<span style="color:green">'''''This update was included in [[GEOS-Chem v11-01 benchmark history#v11-01j|v11-01j]] and approved on 03 Dec 2016'''''</span>
To avoid double-counting of SOA, we do the following:


In [[GEOS-Chem v11-01#v11-01j|GEOS-Chem v11-01j]], PM2.5 concentrations were added to the [[List_of_diagnostics_for_v11-01#ND42:_SOA_diagnostics|ND42 diagnostic for SOA concentrations]]. As part of this update, the code for computing SOA concentrations has been moved from <tt>diag42_mod.F</tt> to routine <tt>AEROSOL_CONC</tt> (in <tt>aerosol_mod.F</tt>). PM2.5 is calculated at the end of <tt>AEROSOL_CONC</tt> following the recommendation by Randall Martin and the Aerosol WG [[#Definition|described above]]. Aerosol growth factors used in the PM2.5 calculation are computed online in the same routine using aerosol densities (stored in the species database) and aerosol radii (stored in <tt>REAA</tt> in <tt>fast_jx_mod.F</tt>).
*When the Complex SOA option is selected, we add '''TSOA + ASOA + ISOAAQ''' to the PM2.5 and AOD diagnostics instead the simple SOA species SOAS.
*Otherwise, we add '''SOAS''' to the PM2.5 and AOD diagnostics instead of TSOA + ASOA + ISOAAQ.


--[[User:Melissa Payer|Melissa Sulprizio]] ([[User talk:Melissa Payer|talk]]) 20:11, 30 November 2016 (UTC)
NOTE: The GEOS-Chem benchmark simulations carry both Simple SOA and Complex SOA species, but only the Simple SOA species (SOAS) is included in diagnostic output.


=== Save out PM2.5 diagnostic at STP conditions ===
=== Save out PM2.5 diagnostic at STP conditions ===
<span style="color:green">'''''This update was included in [[GEOS-Chem v11-02#v11-02a|v11-02a]] and approved on 12 May 2017.'''''</span>


'''''Aaron van Donkelaar wrote:'''''
'''''Aaron van Donkelaar wrote:'''''


<blockquote>As currently implemented [in [[GEOS-Chem v11-01]]], the PM2.5 diagnostic outputs PM2.5 at ambient conditions.  While this is not technically an error, most PM2.5 monitors measure at STP conditions which will cause disagreement during comparison with observations and inconsistency during application of any health response curves (generally determined from the STP observations).<br>
<blockquote>As was originally implemented in [[GEOS-Chem v11-01]], the PM2.5 diagnostic outputs were at ambient conditions.  While this is not technically an error, most PM2.5 monitors measure at STP conditions which will cause disagreement during comparison with observations and inconsistency during application of any health response curves (generally determined from the STP observations).<br>
 
As a result, I’d recommend applying an STP correction factor based on ideal gas law after PM2.5 is calculated in aerosol_mod.F:</blockquote>
 
        PM25(I,J,L) = PM25(I,J,L) * (1013.25d0 / AIRPRESS(I,J,L)) * (AIRTEMP(I,J,L) / 298)
 
--[[User:Melissa Payer|Melissa Sulprizio]] ([[User talk:Melissa Payer|talk]]) 18:05, 7 February 2017 (UTC)
 
== Anthropogenic PM2.5 dust source in GEOS-Chem ==
 
<span style="color:darkorange">'''''NOTE: This update will be implemented in [[GEOS-Chem v11-02|v11-02]].'''''</span>
 
Sajeev Philip and coauthors have added a new PM2.5 dust emission inventory into GEOS-Chem, termed as Anthropogenic Fugitive, Combustion and Industrial Dust (AFCID).  For information on this inventory, please see our [[Mineral_dust_aerosols#Anthropogenic_PM2.5_dust_source_in_GEOS-Chem|''Mineral dust aerosols'' wiki page]].
 
--[[User:Melissa Payer|Melissa Sulprizio]] ([[User talk:Melissa Payer|talk]]) 13:51, 20 March 2017 (UTC)
 
== Past discussions ==
 
'''''[mailto:dxy84123@gmail.com Xinyi Dong] wrote:'''''
 
:I am trying to get PM2.5 from GEOS-Chem and have a question regarding how to sum the aerosol species to get PM2.5. In one paper Tai et al., 2012, the author said "total PM2.5 in GEOS-Chem is taken to be the sum of sulfate, nitrate, ammonium, OC and EC". While in another paper Liu et al., 2004, JGR, the author also include fine dust and sea salt (although he was examing AOT, not exactly PM2.5, but the fine dust aerosols have diameter less than 2.5um). I could not find an official equation for PM2.5 from GEOS-Chem website, so what aerosol species I need to sum in order to get PM2.5 ?
 
:Here is the titles of the two papers:
 
:#Tai et al, 2012: Meteorological modes of variability for fine particulate matter (PM2.5) air quality in the United States: implications for PM2.5 sensitivity to climate change [http://acmg.seas.harvard.edu/publications/Tai_2012a.pdf PDF]
:#Liu et al., 2004: Mapping annual mean ground-level PM2.5 concentration using multiangle imaging spectroradiometer aerosol optical thickness over the contiguous United States.
 
'''''[mailto:jeffrey.pierce@colostate.edu Jeff Pierce] replied:'''''
 
:Sulfate + Nitrate + Ammonium + OC + EC + SOA + FineSeaSalt + FineDust is probably the best bet for PM2.5 (don't forget to convert OC to OM).  However, there is no perfect way in GEOS-Chem since size distributions vary and there will be some fraction of all species that are larger than 2.5 microns.
 
'''''[mailto:dxy84123@gmail.com Xinyi Dong] wrote:'''''
 
:Now I see why [the two papers] use different equations; my understanding is one paper is compared GEOS-Chem with surface observations having few impacts from sea salt and dust, while another compared with satellite AOT, so sea salt and dust were included.
 
:I did a quick search for the conversion from OC to OM, one paper say the OM/OC ratio is 2.1, another say 1.4, so is there an official value suggested for v9-01-02?


'''''[mailto:jeffrey.pierce@colostate.edu Jeff Pierce] replied:'''''
As a result, I’d recommend applying an STP correction factor based on ideal gas law after PM2.5 is calculated:</blockquote>


:OM:OC is an open question!  2.1 is generally more representative of aged organics, 1.4 would be fresh.  I think many people use 1.8 if they choose a single value.
        PM2.5 = PM2.5 * ( 1013.25 / P ) * ( T / 298 )
        PM10 = PM10  * ( 1013.25 / P ) * ( T / 298 )


--[[User:Bmy|Bob Y.]] 16:39, 7 February 2013 (EST)
--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 19:41, 3 November 2021 (UTC)

Latest revision as of 13:32, 4 November 2021

On this page we provide information about how to compute particulate matter concentrations from GEOS-Chem output.

Definitions of PM2.5 and PM10 for GEOS-Chem

PM2.5 definition

Below is the definition of PM2.5 used in GEOS-Chem and approved by the Aerosols Working Group.

This table lists hygroscopic growth factors for PM2.5 constituent species:

Scale factor Multiplies these species Value at 35% RH Value at 50% RH
SIA_GROWTH SO4, NIT, NH4 1.10 1.35
ORG_GROWTH OCPI, SOA 1.05 1.07
SSA_GROWTH SALA 1.86 1.86

The OA changes at both RH, and the SIA change at 50% RH are straightforward changes to yield consistency between with the current Kappa-Kohler hygroscopicity parameterization in GEOS-Chem based on Latimer and Martin (2019).

The SIA recommendation at 35% RH is less certain since it depends on the efflorescence RH of the SIA in the aerosol mixture under the variable conditions of the instruments, collection media, and laboratories involved. Given knowledge gaps about the aerosol phase at low RH, the proposed growth factor of 1.1 assumes that half of the particles are aqueous (growth factor of 1.19 for Kappa-Kohler) and the other half are crystalline (growth factor of unity).

These growth factors are calculated using the change in radius between different RH. Essentially, the change in radius between the dry (i.e. 0% RH) and wet (35% or 50% RH) aerosol is treated as a shell of water for the purposes of calculating the additional mass associated with the wet particle. Under this condition, it can be shown that: 

GrowthFactor = 1 + [{(radiusAtRH_wet / radiusAtRH_dry)^3 - 1} x (Density_Water / Density_DrySpecies)]

Emissions from the Anthropogenic Fugitive, Combustion and Industrial Dust (AFCID) (cf Philip et al (2017) are automatically added to the DST1 bin in most GEOS-Chem simulations. AFCID is activated by default but can be disabled by the user if so desired.

The DST2 bin includes aerosols with diameter both smaller and larger than 2.5 um. Fangqun Yu has recently determined that 30% of DST2 should be included in PM2.5. (The prior value of 38%, which had been established by Duncan Fairlie, Aaron van Donkelaar, Colette Heald, Jeff Pierce and Noelle Selin, was used until GEOS-Chem 13.4.0.)

In summary, PM2.5 at 35% RH should be computed as: 

PM25 = ( NH4 + NIT  + SO4 ) * 1.10
     + BCPI 
     + BCPO 
     + ( OCPO + ( OCPI * 1.05 ) ) * (OM/OC ratio)  # OM/OC ratio = 2.1 by default
     + DST1 
     + DST2 * 0.30                                 # F. Yu suggests 30% of DST2 (Nov 2011); prior value was 38% of DST2
     + SALA * 1.86
     + SOA  * 1.05

By default, the OM/OC ratio is set to a constant value of 2.1. For users who seek more information on the seasonal and spatial variation of OM/OC in the lower troposphere, we provide the option to use the seasonal gridded dataset developed by Philip et al. (2014). This dataset has some uncertainty, but offers more information than a global-mean OM/OC ratio in regions where primary organic aerosols have a large fossil fuel source.

NOTE: Some modifications to this basic definition are necessary, depending on the SOA species that are used in a given GEOS-Chem simulation. See the PM2.5 and PM10 diagnostics for GEOS-Chem section below for details.

PM10 definition

In GEOS-Chem 13.4.0 and later versions, PM10 at 35% RH is computed according to the following formula: 

PM10 = PM2.5 
     + ( DST2 * 0.7  )
     + DST3
     + ( DST4 * 0.9  )
     + ( SALC * 1.86 )   # NOTE: The value of 1.86 is the SSA_GROWTH factor at 35% RH

The constant scale factors for DST2 (70%) and DST4 (90%) were determined by Fanqun Yu from APM aerosol microphysics simulations. For more information, please follow this link..

NOTE: Some modifications to this basic definition are necessary, depending on the SOA species that are used in a given GEOS-Chem simulation. See the PM2.5 and PM10 diagnostics for GEOS-Chem section below for details.

PM2.5 and PM10 diagnostics for GEOS-Chem

The PM2.5 and PM10 diagnostics belong to the the AerosolMass collection in the GEOS-Chem History diagnotics). They are computed according to the code below, which may be found in GeosCore/aerosol_mod.F90. 

       !==============================================================
       ! P A R T I C U L A T E   M A T T E R
       !
       ! See this GEOS-Chem wiki page for the most up-to-date
       ! definitions of PM2.5 and PM10 used in GEOS-Chem:
       !
       ! http://wiki.geos.chem.org/Particulate_Matter_in_GEOS-Chem
       !==============================================================

       ! Particulate matter < 2.5um [kg/m3]
       PM25(I,J,L) = NH4(I,J,L)        * SIA_GROWTH + &
                     NIT(I,J,L)        * SIA_GROWTH + &
                     SO4(I,J,L)        * SIA_GROWTH + &
                     BCPI(I,J,L)                    + &
                     BCPO(I,J,L)                    + &
                     OCPO(I,J,L)                    + &
                     OCPI(I,J,L)       * ORG_GROWTH + &
                     SALA(I,J,L)       * SSA_GROWTH + &
                     SOILDUST(I,J,L,1)              + &   ! + 100% of DST1
                     SOILDUST(I,J,L,2)              + &   !
                     SOILDUST(I,J,L,3)              + &   ! 
                     SOILDUST(I,J,L,4)              + &   ! 
                     SOILDUST(I,J,L,5) * 0.3_fp           ! + 30%  of DST2

       ! Particulate matter < 10um [kg/m3]
       PM10(I,J,L) = PM25(I,J,L) +                    &   ! PM2.5
                     SOILDUST(I,J,L,5) * 0.7_fp     + &   ! + 70%  of DST2
                     SOILDUST(I,J,L,6)              + &   ! + 100% of DST3
                     SOILDUST(I,J,L,7) * 0.9_fp     + &   ! + 90%  of DST4
                     SALC(I,J,L)       * SSA_GROWTH

       ! Include either simple SOA (default) or Complex SOA in
       ! PM2.5 calculation.  In simulations where both Simple SOA and
       ! Complex SOA species are carried (i.e. "benchmark"), then
       ! only the Simple SOA will be added to PM2.5, in order to avoid
       ! double-counting. (bmy, 5/11/18)
       IF ( Is_SimpleSOA ) THEN
          PM25(I,J,L) = PM25(I,J,L) + ( SOAS(I,J,L) * ORG_GROWTH )
          PM10(I,J,L) = PM10(I,J,L) + ( SOAS(I,J,L) * ORG_GROWTH )

       ELSE IF ( Is_ComplexSOA ) THEN 
          PM25(I,J,L) = PM25(I,J,L)                 + &
                        TSOA(I,J,L)   * ORG_GROWTH  + &
                        ASOA(I,J,L)   * ORG_GROWTH  + &
                        ISOAAQ(I,J,L) * ORG_GROWTH        ! Includes SOAGX

          PM10(I,J,L) = PM10(I,J,L)                 + &  
                        TSOA(I,J,L)   * ORG_GROWTH  + &
                        ASOA(I,J,L)   * ORG_GROWTH  + &
                        ISOAAQ(I,J,L) * ORG_GROWTH        ! Includes SOAGX

          ! Need to add OPOA to PM2.5 for complexSOA_SVPOA simulations
          ! -- Maggie Marvin (15 Jul 2020)
          IF ( Is_OPOA ) THEN
             PM25(I,J,L) = PM25(I,J,L) + ( OPOA(I,J,L) * ORG_GROWTH )
             PM10(I,J,L) = PM10(I,J,L) + ( OPOA(I,J,L) * ORG_GROWTH )
          ENDIF
       ENDIF

       ! Apply STP correction factor based on ideal gas law
       PM25(I,J,L) = PM25(I,J,L) * ( 1013.25_fp / PMID(I,J,L) ) * &
                                   ( T(I,J,L)  / 298.0_fp     )

       PM10(I,J,L) = PM10(I,J,L) * ( 1013.25_fp / PMID(I,J,L) ) * &
                                   ( T(I,J,L)   / 298.0_fp    )

Also note that there are some calculations that were not included in the basic definitions of PM2.5 and PM10 in the preceding sections. These are:

Avoid double-counting of ISOAAQ species

Jenny Fisher rightly pointed out that the PM2.5 diagnostic was erroneously including the ISOAAQ species in the accounting of PM2.5 when the Simple SOA option was used. After discussion with the Aerosols Working Group, we modified the PM2.5 and PM10 diagnostic computations accordingly:

To avoid double-counting of SOA, we do the following:

  • When the Complex SOA option is selected, we add TSOA + ASOA + ISOAAQ to the PM2.5 and AOD diagnostics instead the simple SOA species SOAS.
  • Otherwise, we add SOAS to the PM2.5 and AOD diagnostics instead of TSOA + ASOA + ISOAAQ.

NOTE: The GEOS-Chem benchmark simulations carry both Simple SOA and Complex SOA species, but only the Simple SOA species (SOAS) is included in diagnostic output.

Save out PM2.5 diagnostic at STP conditions

Aaron van Donkelaar wrote:

As was originally implemented in GEOS-Chem v11-01, the PM2.5 diagnostic outputs were at ambient conditions. While this is not technically an error, most PM2.5 monitors measure at STP conditions which will cause disagreement during comparison with observations and inconsistency during application of any health response curves (generally determined from the STP observations).
As a result, I’d recommend applying an STP correction factor based on ideal gas law after PM2.5 is calculated:

        PM2.5 = PM2.5 * ( 1013.25 / P ) * ( T / 298 )
        PM10  = PM10  * ( 1013.25 / P ) * ( T / 298 )

--Bob Yantosca (talk) 19:41, 3 November 2021 (UTC)

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