Earthdata Forum

Hi there,

Recently I am using the M2T1NXAER (tavg1_2d_aer_Nx) collection to study long-term variations of aerosols. I have a few questions regarding the Surface Mass Concentration variables in the product.

For the variables SSSMASS, DUSMASS, BCSMASS, and OCSMASS — do these represent the total mass concentration near the surface across all size bins (i.e., particles < 10 μm for SS/DU, and both hydrophobic and hydrophilic particles for BC/OC), or are they specific to certain bins?

I also noticed there are separate variables like SSSMASS25. Assuming SSSMASS already includes all size bins, does that mean SSSMASS25 is for particles < 2.5 μm sea salt aerosol?

Thanks in advance for any clarification you can provide!

Thank you for your interest in MERRA-2 aerosol data! You are correct in your understanding of the fields. SSSMASS, DUSMASS, BCSMASS, and OCSMASS include all five size bins for sea salt and dust, and both hydrophobic and hydrophilic for black and organic carbon. SSSMASS25 and DUSMASS25 only contain the portion with a geometric diameter smaller than 2.5 microns.

If you study the long-term change of aerosols, you may want to consider the monthly aerosol collection tavgM_2d_aer_Nx (M2TMNXAER).

Adding to Allie's reply, which is good, the MERRA-2 FAQ may provide you additional information (https://gmao.gsfc.nasa.gov/gmao-products/merra-2/faq_merra-2/). You can search "PM" and "bin".

acollow wrote: ↑Tue Jan 13, 2026 8:07 am America/New_York Thank you for your interest in MERRA-2 aerosol data! You are correct in your understanding of the fields. SSSMASS, DUSMASS, BCSMASS, and OCSMASS include all five size bins for sea salt and dust, and both hydrophobic and hydrophilic for black and organic carbon. SSSMASS25 and DUSMASS25 only contain the portion with a geometric diameter smaller than 2.5 microns.

Thanks a lot!!!

GES DISC - xpan2 wrote: ↑Tue Jan 13, 2026 10:14 am America/New_York If you study the long-term change of aerosols, you may want to consider the monthly aerosol collection tavgM_2d_aer_Nx (M2TMNXAER).

Adding to Allie's reply, which is good, the MERRA-2 FAQ may provide you additional information (https://gmao.gsfc.nasa.gov/gmao-products/merra-2/faq_merra-2/). You can search "PM" and "bin".

Thanks! I will check the monthly collection and the FAQ. Much appreciated!