In talking about particulate and what is there, as well as how it came to be there? The US E.P.A. puts it this way, in their glossary of terms:
Particulate matter that consists of compounds of sulfur formed by the interaction of sulfur dioxide and sulfur trioxide with other compounds in the
atmosphere. Sulfate aerosols are injected into the atmosphere from the combustion of fossil fuels and the eruption of volcanoes like Mt.
Pinatubo. Sulfate aerosols can lower the Earth's temperature by reflecting away solar radiation (negative radiative forcing). General Circulation
Models which incorporate the effects of sulfate aerosols more accurately predict global temperature variations. See particulate matter, aerosol,
General Circulation Models. 
This is a process the world has seen before and in dramatic fashion. When the Island volcano of Krakatoa blew itself into history, the shockwave
traveled the planet multiple times. It was heard over clear out in Australia and is thought of as the loudest noise ever heard or recorded by man.
The Skies Change
In the weeks following the eruption, fine fragments of tephra and dust that were propelled kilometers into the stratosphere began to make a ring
around the equator. They would remain suspended there for years causing remarkable solar effects and atmospheric hazing as they bent the incoming
light. Also the enormous volumes of sulfur dioxide gas molecules that were ejected into the atmosphere combined with water to make sulfuric acid.
These acidic aerosols sufficiently blocked enough sunlight to drop the Earth's temperature by several degrees for a few years.
Physical Geology - Krakatoa Eruption
Highlighted here is the natural process the eruption triggered and what some approaches to SRM seek to imitate or duplicate through atmospheric
manipulation and balance.
Is spraying (injecting) anything into the atmosphere a good idea? Is it a bridge too far in what they seek to accomplish or is this, itself, bordering
on too little and too late?
More to the point of how this impacts the forum overall? What might the injection of both particulate into layers of the stratosphere or dispersal of
liquid in "cloud whitening" look like exactly?
Perhaps a better question....do we need wonder or is it possible some have already seen prototype and experimental viability studies being conducted
with real aircraft?
Now every good thread needs at least a LITTLE eye candy in my view. It's what we expect and best understand in many scientific concepts. So, not one
to disappoint, I've come with a bit of eye candy to add as well.
The first one here is an overall graphic depiction of SRM and overall climate mitigation efforts as they may play out in 3 dimensional space. It's an
interesting look and suggests a bit how they may well interact to make the different methods either more or less effective by that interaction. I
wonder if enough real world testing has been done for what is being discussed to know with confidence, which side of benefit vs. challenge that may
I include this second one as an interesting view of how broadly the layers of the atmosphere are depicted. As we learned by the NWS/NOAA definitions
(and NASA has similar material we've seen posted before as well), the Stratosphere layer can start as low as just over 21,000 feet or, in other
conditions, much much higher. (It's generally quite a bit higher, to be realistic)
Again, it's a fluid layer as the atmosphere itself is a very dynamic system in a constant state of change from one moment to the next.
I do hope that when active measures are the order of the day for efforts to be taken, the certainty is well beyond the level I find it's at now.
There is as much speculation in things like the IPCC/UN conferences as there are declarations of fact. At least where mitigation methods are concerned
and how injecting new matter into the atmosphere may be accomplished to what end result.
** I also need to note that I am more or less on a vacation right now, so I'm checking in once a day on average and only for a short time. Vacation
means doing what I love to do though, and writing informational pieces is among my true enjoyments in life. So, forgive me if I may not reply in my
usual time and manner. It may take a day to get back on anything specific.