Dear Parth,

Are you using the NASA GES DISC Aerosol Index or a national data set available in your country? As you will see from

http://disc.sci.gsfc.nasa.gov/data-holdings/PIP/aerosol_index.shtml

that index "detects the presence of uv-absorbing aerosols such as dust and soot".

The proper interpretation of that index is explained later on as follows: "Positive values of Aerosol Index generally represent absorbing aerosols (dust and smoke) while small or negative values represent non-absorbing aerosols and clouds. The Index can be interpreted in terms of optical depth if the index of refraction, particle size distribution, and the height of the aerosol layer are known from other measurements."

Hence this index primarily reports on the absorbing properties of the aerosols in the UV spectral domain. It does not, per se or alone, say anything about the size distribution of the airborne particles, though such information may be derived if multiple other variables are fully specified.

On the other hand, PM10 (and PM2.5) values are indicators of the number of airborne particles of 10 (2.5) micrometers in size or less

http://en.wikipedia.org/wiki/Particulates

irrespective of their chemical composition, and thus of their possible impact in absorbing UV radiation.

There may be a weak link between these two indicators, but it is certainly non trivial. The main question is why did you pick these two indicators or try to relate them a priori? Do you expect a relation? If so, which one and why? What is your hypothesis or starting point?

Cheers, Michel.

A short addendum

In Wikipedia the term PM is not defined?!

PM should define the mass (concentration) of airborne particulates with an aerodynamic size smaller than the indicated diameter; even more specific: of particulates that pass an inlet with a size selective separator with a 50% cut-off at the indicated size and a specification of the transmission of larger particulates.

summary: PM is defined as a rather complex entity and as mass

Thank you Prof. Verstraete and Prof Brink for your replies. As suggested I would look more into it and check.

Dear Parth,

aerosol measurements performed at the ground do not necessarily show the

same seasonal cycle of those measurements referring to the aersol loads in the whole atmospheric column. This is due to several factors, one major one

being the different aerosol vertical distribution over the year.

On this aspect, you may find some insight into the opposite seasonal cycle of AOD and PM in a study performed in Italy (Barnaba et al, JGR 2010), which is available

here in Reserch Gate. Hope this could help you,

cheers from Italy,

Francesca

Thank you Dr. Barnaba for your kind inputs. I would surely read your article "Annual cycle in co-located in situ, total-column, and height-resolved aerosol observations in the Po Valley (Italy): Implications for ground-level particulate matter mass concentration estimation from remote sensing ".

However, I wanted to know something regarding the use of UV aerosol index and ground based PM measurements.

Thanks and regards,

Parth

We should also consider that the UV aerosol index is focussed on the interaction of the aerosols with UV solar radiation and it could be also quite different to consider the AOD at 550 nm (the most used AOD).

Yes Dr Luis I agree. That's what I want to know about UV aerosol index and any relation to PM measured at ground?

It is true that AI in the UV is different from AOD in the visible. My point was just that caution should be paid when comparing/relating an in situ with a columnar aerosol

measurement.

AI is for absorption so a measure for the columnar amount of soot and possibly colored minerals. So why should there be a relation with surface mass concentration of total aerosol?