### MERRA-2 PM 2.5 vs. PM 10

Posted:

**Tue Jul 19, 2022 9:48 pm America/New_York**Hello,

I am reconstructing MERRA-2 sourced PM 10 and PM 2.5. My primary question is it correct to assume that PM 10 will ALWAYS be greater than PM 2.5?

My follow up question is can you offer any comments on equations for PM 2.5 and PM 10 shown here: https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2/FAQ/

Previously there had not been an equation for PM 2.5, and the one that I had used differs slightly. Are these the official or best practice equations for calculating PM 2.5 and PM 10? Are they subject to change?

For PM 2.5 when an equation was not provided I turned to literature and found several options. I chose one based of this paper https://link.springer.com/article/10.1007/s11869-015-0338-3

It differs slightly, with an OC coffeiecient of 1.8, which I suspect is why I am seeing PM 2.5 exceed PM 10 in some cases.

This is the current equation I am using.

PM2.5 (kg/m^3) = DUSMASS25 + SSSMASS25 + BCSMASS + (1.8 * OCSMASS) + (1.375 * SO4SMASS)

Any thoughts, comments or advice is appreciated!

Thanks!

I am reconstructing MERRA-2 sourced PM 10 and PM 2.5. My primary question is it correct to assume that PM 10 will ALWAYS be greater than PM 2.5?

My follow up question is can you offer any comments on equations for PM 2.5 and PM 10 shown here: https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2/FAQ/

Previously there had not been an equation for PM 2.5, and the one that I had used differs slightly. Are these the official or best practice equations for calculating PM 2.5 and PM 10? Are they subject to change?

For PM 2.5 when an equation was not provided I turned to literature and found several options. I chose one based of this paper https://link.springer.com/article/10.1007/s11869-015-0338-3

It differs slightly, with an OC coffeiecient of 1.8, which I suspect is why I am seeing PM 2.5 exceed PM 10 in some cases.

This is the current equation I am using.

PM2.5 (kg/m^3) = DUSMASS25 + SSSMASS25 + BCSMASS + (1.8 * OCSMASS) + (1.375 * SO4SMASS)

Any thoughts, comments or advice is appreciated!

Thanks!