# Difference between revisions of "Particulate matter in GEOS-Chem"

## Definition of PM2.5 used in GEOS-Chem

by Randall Martin, Daven Henze, Aaron van Donkelaar, and Jeff Pierce:

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 often used and would be appropriate for the benchmark. In Europe an RH of 50% is often used.

Below are the factors that account for aerosol water in a consistent manner as calculated by Aaron van Donkelaar and Sajeev Philip.

At 35% RH:

• 1.33 for SO4, NIT, and NH4
• 1.16 for OCPI and SOA
• 1.86 for SALA

At 50% RH the values are

• 1.51 for SO4, NIT, and NH4
• 1.24 for OCPI and SOA
• 2.42 for SALA

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)]
```

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.

In summary, PM2.5 should be computed as:

```PM25 = (NH4 + NIT  + SO4) * 1.33
+ BCPI
+ BCPO
+ (OCPO + (OCPI * 1.16)) * 2.1
+ DST1
+ DST2 * 0.38
+ SALA * 1.86
+ SOA  * 1.16

NOTE: 2.1 = ratio of OM/OC
```

In GEOS-Chem 13.0.0 and later versions, SOA is defined as:

When using the Simple SOA option:

• SOAS = Simple SOA (150 g/mol)

When using the Complex SOA option:

• TSOA0, TSOA1, TSOA2, TSOA3 = Lumped semivolatile aerosol products of monoterpene + sesquiterpene ox.
• ASOAN, ASOA1, ASOA2, ASOA3 = Lumped nonvolatile aerosol products of light aromatics and IVOCs
• ISOAAQ = Isoprene SOA from aqueous formation, includes
• SOAGX = Aerosol-phase glyoxal (58 g/mol)
• SOAIE = Aerosol-phase isoprene epoxide (118 g/mol)
• LVOCOA = Aerosol-phase low-volatility non-IEPOX product of ISOPOOH (RIP) oxidation (154 g/mol)

NOTE: Fisher et al (2016, ACP) recommend to Exclude INDIOL from AOD and aerosol mass calculations, as it results in lost mass. As noted in Fisher et al. (2016, ACP), this is a source of uncertainty and would benefit from an update when more information about this process becomes available.

### Option to include spatially and seasonally varying OM/OC

This update was included in v11-02e (approved 24 Mar 2018).

For users who seek more information on the seasonal and spatial variation of OM/OC in the lower troposphere (which by default is set to a constant value of 2.1), 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.

## PM2.5 diagnostic as implemented in GEOS-Chem

The PM2.5 diagnostic (which belongs to the the AerosolMass collection in the GEOS-Chem History diagnotics) is computed according to the code below.

```       !==============================================================
! P A R T I C U L A T E   M A T T E R
!
! Compute PM2.5 concentration [kg/m3]
!
! PM25 = 1.33 (NH4 + NIT  + SO4) + BCPI + BCPO +
!        2.10 (OCPO + 1.16 OCPI) + 1.16 SOA*   +
!        DST1 + 0.38 DST2 + 1.86 SALA
!
!   * If using simple  SOA, SOA = SOAS;
!     If using complex SOA, SOA = TSOA + ASOA + ISOAAQ
!
! NOTES:
! - We apply growth factors at 35% RH (computed above):
!    1.33 for SO4, NIT, and NH4
!    1.16 for OCPI and SOA
!    1.86 for SALA
! - Ratio of OM/OC = 2.1 is applied to OCPI and OCPO above
! - Aerosol WG recommends including 38% of DST2 in PM2.5
! - Use either simple SOA or complex SOA in PM2.5 calculation.
!   By default simple SOA will be used.
!
! %%% IMPORTANT %%%
! Note that if complex SOA is used then PM2.5 includes all
! the SOA formed in both the Marais et al. and Pye et al.
! schemes and may include some double-counting of isoprene SOA.
! (Aerosol WG)
!==============================================================

! Units: [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)              + & ! DST1
SOILDUST(I,J,L,2)              + & ! DST1
SOILDUST(I,J,L,3)              + & ! DST1
SOILDUST(I,J,L,4)              + & ! DST1
SOILDUST(I,J,L,5) * 0.38           ! 38% of DST2

! 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
ELSEIF ( 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

! 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
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    )
```

### 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 diagnostic (in routine aerosol_mod.F90) 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 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).
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:
```        PM25(I,J,L) = PM25(I,J,L) * (1013.25d0 / AIRPRESS(I,J,L)) * (AIRTEMP(I,J,L) / 298)
```

This has since been added to the PM2.5 diagnostic in GEOS-Chem (see code above).

## Anthropogenic PM2.5 dust source in GEOS-Chem

This update was included in GEOS-Chem 12.1.0, which was released on 26 Nov 2018.

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 wiki page.

--Bob Yantosca (talk) 22:27, 11 January 2019 (UTC)

## PM10

At present there is no PM10 diagnostic in GEOS-Chem. We welcome GEOS-Chem User Community to assist us with implementing this diagnostic.

--Bob Yantosca (talk) 15:02, 22 February 2021 (UTC)