Magnitude and Unit of PM2.5, MERRA-2: Conversion Necessary?

[mgreene]

Hello,
The equation for PM2.5 is the same as what we have posted on our FAQ page, so that is correct. (https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2/FAQ/) I think this should work equally well for 1 hourly or 1 monthly calculations.

As to why “the pixel size of the original five parameters (dusmass25/ocsmass/bcsmass/sssmass25/so4smass) is not the same as the pixel size of the monthly mean value of the pm2.5 concentration” it is not quite possible for anyone here to say, as it is a function of the software and routine that the user are using to make the calculations to compute the data.

Hope this helps.

[hemraj]

I do not understand why MERRA2 ignores nitrate aerosol while calculating PM2.5. Does anyone help me to understand the reason.

GEOS and GOCART2G consider nitrate, while MERRA2 doesn't as shown in the pdf below.

https://gmao.gsfc.nasa.gov/pubs/docs/Collow1489.pdf

[acollow]

Hello,
Thank you for your interest in using MERRA-2 to compute PM2.5. GEOS is constantly evolving over time as advancements are made to the underlying model, including the GOCART aerosol module. Reanalyses such as MERRA-2 use a frozen version of the model so that the long term time series is consistent. The capability to model nitrate in GOCART became operational after the model was frozen for MERRA-2.

[GES DISC - xpan2]

Good question. When generating the MERRA-2, the GEOS model didn't have the nitrate aerosol in the aerosol module. As you might know, MERRA-2 has been generated with a consistent model version 5.12.4 as designed. This is why the recent MERRA-2 data still has no nitrate, although GOCART2G has nitrate.