CAMRO-Dust: MERRA2 Based PM2.5 and Dust data
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PM2.5 and Dust2.5 mass concentrations at ground level are calculated from aerosol components (sulfate, organic matter, black carbon, size-resolved dust and sea salt) in the NASA MERRA-2 Reanalysis product using both aerodynamic and geometric diameter as a cut-off size. Observations of PM2.5 have been reported using both aerodynamic diameter and geometric diameter as a cut-off size, at dry and ambient conditions, depending on instruments and measuring methods. It is important that the model outputs are reported to be consistent with observations for fair comparisons. As shown in Yang et al. (2022), the use of geometric diameter in defining PM2.5 would result in PM2.5 higher by about a factor of 2 than that using the aerodynamic diameter in dust dominated regions.
The aerodynamic diameter and geometric diameter have the following relationship:
Dae=Dgeo*part/water
where Dae is the aerodynamic diameter, Dgeo is the geometric diameter, ρparl is the density of the particle (ρwater is the density of water, χ is the shape factor (Reid et al., 1994, Collow et al., 2023).
| Species | BC | OC | Du Bin 1 | Du Bin 2 | SS | SU |
| Density (kg/m3) | 1800 | 1800 | 2500 | 2650 | 2200 | 1700 |
where BC: black carbon; DU: dust; OC: organic matter (organic carbon * 1.8); SS: sea salt; SO4: sulfate. Dust Bin 1: 0.2-2μm geometric diameter; Bin 2: 2-3.6μm geometric diameter.
Shape factor for dust χ = 1.4 (Alexander et al., 2016; Chin personal communication)
For hydrophilic species, we consider RH (relative humidity) = 0% (dry), 35% (typical EPA FRM measurement condition), and ambient value calculated in the MERRA2. Growth factors are calculated following Collow et al., 2023, similar to MERRA-2.
PM2.5_A_Dry: Dry Aerodynamic PM2.5
Description: Black Carbon (hydrophilic + hydrophobic); Organic Carbon (hydrophilic + hydrophobic); 96.14% of Dust Bin1 (geometric diameter: 0.2-2μm); Sea Salt (Bin1 + Bin2 + 47.52% of Bin 3 (geometric diameter (1-3μm)); ammonium sulfate.
Formula: BCPHILIC + BCPHOBIC + OCPHILIC + OCPHOBIC + 0.9614*DU001 + SS001 + SS002 + 0.4752*SS003 + 1.3756*SO4
PHILIC: hydrophilic, solvable to water; PHOBIC: hydrophobic, insolvable; 001: size bin #1; 002: size bin #2.
PM2.5_A_Wet: Aerodynamic PM2.5 at Ambient RH conditions
Description: Black Carbon (hydrophilic at ambient RH condition + hydrophobic); Organic Carbon (hydrophilic at ambient RH condition + hydrophobic); 96.14% of Dust Bin1 (geometric diameter: 0.2-2μm); Sea Salt at ambient RH condition (Bin1 + Bin2 + 47.52% of Bin3 (geometric diameter (1-3μm)); ammonium sulfate at ambient RH condition.
Formula: f_RH_BC*BCPHILIC + BCPHOBIC + f_RH_OC*OCPHILIC + OCPHOBIC + 0.9614*DU001 + f_RH_SS*SS001 + f_RH_SS*SS002 + f_RH_SS*0.4752*SS003 + f_RH_SO4*1.3756*SO4, where f_RHs are the species specific growth factors.
PM2.5_A_RH35: Aerodynamic PM2.5 at RH=35%, average EPA FRM measurement condition
Description: Black Carbon (hydrophilic at RH=35% + hydrophobic); Organic Carbon (hydrophilic at RH=35% + hydrophobic); 96.14% of Dust Bin1 (geometric diameter: 0.2-2μm); Sea Salt at RH=35% (Bin1 + Bin2 + 47.52% of Bin3 (geometric diameter (1-3μm)); ammonium sulfate at RH=35%.
Formula: f_RH35_BC*BCPHILIC + BCPHOBIC + f_RH35_OC*OCPHILIC + OCPHOBIC + 0.9614*DU001 + f_RH35_SS*SS001 + f_RH35_SS*SS002 + f_RH35_SS*0.4752*SS003 + f_RH35_SO4*1.3756*SO4
PM2.5_G_Dry: Dry Geometric PM2.5
Description: Black Carbon (hydrophilic + hydrophobic); Organic Carbon (hydrophilic + hydrophobic); Dust (Bin 1 + 37.96% Bin2 (geometric diameter: 2-3.6μm)); Sea Salt (Bin 1 + Bin 2 + 84.40% of Bin 3 (geometric diameter (1-3μm)); ammonium sulfate.
Formula: BCPHILIC + BCPHOBIC + OCPHILIC + OCPHOBIC + DU001 + 0.3796*DU002 + SS001 + SS002 + 0.83404*SS003 + 1.3756*SO4
PM2.5_G_Wet: Geometric PM2.5 at Ambient RH
Description: Black Carbon (hydrophilic at ambient RH condition + hydrophobic); Organic Carbon (hydrophilic at ambient RH condition + hydrophobic); Dust (Bin1+37.96% Dust Bin2 (geometric diameter: 2-3.6μm)); Sea Salt at ambient RH condition (Bin1 + Bin2 + 84.40% of Bin3 (geometric diameter (1-3μm)); ammonium sulfate at ambient RH condition.
Formula: f_RH_BC*BCPHILIC + BCPHOBIC + f_RH_OC*OCPHILIC + OCPHOBIC + DU001 + 0.3796*DU002 + f_RH_SS*SS001 + f_RH_SS*SS002 + f_RH_SS*0.83404*SS003 + f_RH_SO4*1.3756*SO4
PM2.5_G_RH35: Geometric PM2.5 at RH=35%, EPA FRM condition
Description: Black Carbon (hydrophilic at RH=35% + hydrophobic); Organic Carbon (hydrophilic at RH=35% + hydrophobic); Dust (Bin1+37.96% Dust Bin2 (geometric diameter: 2-3.6μm)); Sea Salt at RH=35% (Bin1 + Bin2 + 84.40% of Bin3 (geometric diameter (1-3μm)); ammonium sulfate at RH=35%.
f_RH35*BCPHILIC+BCPHOBIC+f_RH35*OCPHILIC+OCPHOBIC+DU001+0.3796*DU002+f_RH35*SS001+f_RH35*SS002+f_RH35*0.83404*SS003+f_RH*1.3756*SO4
Dust2.5_A: Dry Aerodynamic Dust PM2.5
Description: 96.14% of Dust Bin1 (geometric diameter: 0.2-2μm).
Formula: 0.9614*DU001
Dust2.5_G: Dry Geometric Dust
Description: Dust Bin1 + 37.96% Bin2 (geometric diameter: 2-3.6μm)
Formula: PM2.5: DU001+0.3796*DU002
Time resolution: daily average calculated from the MERRA-2 3-hour instantaneous outputs.
Temporal coverage: 1998 Jan. – 2024 Nov.
Spatial resolution: 0.625 degree (longitude) x 0.5 degree (latitude)
Spatial coverage: global
Format: NetCDF4
Reference
Alexander, J. M., Bell, D. M., Imre, D., Kleiber, P. D., Grassian, V. H., & Zelenyuk, A. (2016). Measurement of size-dependent dynamic shape factors of quartz particles in two flow regimes. Aerosol Science and Technology, 50(8), 870–879, 2016 https://doi.org/10.1080/02786826.2016.1200006
Collow, A., V. Buchard, M. Chin, P. Colarco, A. Darmenov, and A. da Silva, 2023: Supplemental Documentation for GEOS Aerosol Products. GMAO Office Note No. 22 (Version 1.0), 8 pp, available from http://gmao.gsfc.nasa.gov/pubs/office_notes.
Reid, J., T. Cahill, P. H. Wakabayashi, M. R. Dunlap, Geometric/aerodynamic equivalent diameter ratios of ash aggregate aerosols collected in burning Kuwaiti well fields, Atmos. Envi, V 28, p 2227-2234, 1994, https://doi.org/10.1016/1352-2310(94)90362-X.
Yang A., Q. Tan, C. Rajapakshe, M. Chin and H. Yu. Global premature mortality by dust and pollution PM2.5 estimated from aerosol reanalysis of the modern-era retrospective analysis for research and applications, version 2, Frontiers in Environmental Science, 10, [10.3389/fenvs.2022.975755], 2022.