Yes it matters and lots has been published on this question. For instance see journals of AGU [American Geophysical Union]. To be clear let's understand the definition of an aerosol is that it is a suspension of particles in a gas. Although a second common usage meaning is that an aerosol is a particle.

However to understand the functions of atmospheric aerosols we have to stick with the long standing scientific definition because interactions among the particulate and gas phases are important factors in how much location matters.

The summary from newscenter has the broad brush roughly correct in distinguishing location in the troposphere from that in the stratosphere. It also mentions that influence of location is also a function of the chemical nature of the particles. Another important factor is the physical nature of the particles. Particles with many different chemical and physical characteristics exist simultaneously in variable proportions as a function of time, temperature, pressure, radiation and location within the troposphere and stratosphere. Characterizing them all and accounting for all the complex change processes across the atmospheric spaces and time remains a major challenge and weakness in achieving needed certainty for predicting the influence of geophysical and anthropogenic processes on climate., etc.

Rohit really it's major concern in monsoon systems .. studies from ramanathan et al ., shows it effects the hydrological cycle.mainly Black carbon (BC) particle acts as an cloud condensation nuclei due to that the size of the amount of but still there is some uncertainty in these cases. but generally as surabi stated these short lived climate species(SLCF's) like BC are major responsible for warming by curbing these SLCF's we can mitigate the near term climate change.

Dear Rohit,

I want to add some additional points to clear your doubts.

1. "If an aerosol is in the lower atmosphere, it's affected by the weather and it precipitates back down right away,"

Response: In general aerosols in lower atmosphere have life time ranging from 2-7 days depending on their chemical composition, size and meteorlogy of ambient atmosphere. There is particularly two way of removing these particles from the atmosphere: wet removal and dry removal. Apart from these removal processes, meteorology also affects the long range transportation (LRT) of these aerosols particles via vertical and horizontal transportation especially in summer seasons (when convective activities are at their peak). This type of long range transportation (LRT) or in some case regional transportation allow to mix different type of aerosols in some geographical regions such as Indo-gangetic basin. Recent studies (Kim and Lau, 2006) suggested that the existence of such mixed (dust and BC) vertically elevated aerosols near the southern slope of Himalyas significantly changes the temperature profile of atmosphere and thus, affecting the south west mosnsoon patterns over India.

However, the precipitation of aerosols particles via wet removal depends on monsoon system and it is not neccesary to precipitates back down right away, as i mentioned about regional and long range transportation.

2. Bourassa says. "Once it reaches the stratosphere, it can persist for years, and with that kind of a sustained lifetime, it can really have a lasting effect."

Response: Definately, when aerosols reaches the stratosphere, their life time increases significantly. However, in very few cases these aerosols can lift up to upper troposphere or lower stratosphere (Volcanic activities or some boreal wild fire activities). These aerosols in upper troposphere and lower stratosphere (majorly sulphates and organic carbons) affects the climate indirectly (via formation of cirrus clouds). Their direct effect is still not a matter of concern in stratosphere because of very low concentartion of these lifted aerosol particles.

HOPE THESE POINTS SHOULD CLEAR YOUR DOUBTS.

Of importance is also the underlying surface. An example is reflecting aerosol above snow-covered land o cloud does NOT exert a cooling effect.

Similarly light-absorbing carbon (Black Carbon) above the sea hardly absorbs more solar radiation than the sea surface itself.

I will add my voice to the very good answers provided already and respond that yes it matters where the aerosols are in the vertical. But yet it remains a complex question. Apart from their radiative effect in cloudless skies through their chemical composition and size-dependent scattering and absorption properties, aerosols can affect the life cycle of different types of clouds depending on their location (e.g. cirrus vs marine stratocumulus for example). These different cloud types have different effects on climate, on which aerosols can exert various influences. For instance, it is true that light-absorbing aerosols in the lower atmosphere over a dark sea surface do not drastically change the energy balance of the system. However if such aerosols have been activated as cloud droplets to form a marine stratocumulus cloud layer, their absorbing properties may drastically change the life cycle the cloud layer and radiative properties and hence the heat budget of the atmosphere/ocean. Light-absorbing aerosols may lead to reduced cloudiness during the day and reduce the reflective effect of the low-level marine clouds resulting in more heat being absorbed by the ocean. The following paper by Ackerman et al. nicely discusses this subject.

Ackerman, A.S., O.B. Toon, D.E. Stevens, A.J. Heymsfield, V. Ramanathan, and E.J. Welton, 2000: Reduction of tropical cloudiness by soot. Science, 288, 1042-1047.

Rohit

I went to the original question and I like to know what you really wnat to know.

You cite a certain "Bourassa". I googled him and noticed that he studies stratospheric aerosols from volcanic eruptions. This is not really related to the subject of Climate Change.

The melting of gletchers is a completely different issue. The mentioned referecne discusses the effect of soot/black carbon in the Hymalayas. But I do not see what this has to do with your question whereabouts the aerosols are in the atmosphere.

In this case the black carbon also deposits onto the ice/snow and atays there for a year. This soot absorbs sunlight and heats up the ice.

Bhaski

I went to your site and notice that you are an expert in the regional climate in S-Asi, so I hesiate to put in my knowledge on the regional aerosol in Europe north of the Alps. In Europe BC is confined to the lowe troposphere, which mostly is limited to anything like 850-700 mbar level. However, Iin the Alpine region the lower troposphere can exttend up to 4000 m. Still, the average concentration on Jungfraujoch at this height is very low, compared to that in the valleys of Switzerland. This might answer your question where the BC preferentially resides in the atmosphere.

The lifetime of BC is governed by its removal via precipitation, exactly the process that delivers it to the glaciers in the mountains. The BC produced in India mainly in the course of cooking is continuously provided and in the prevailing SW is carried along with the monsoon winds

Subari (Menon) mentions the uncertainty in the BC emissons which emans that the share of BC to the melting might even be larger than what she models in the mentioned paper that I just reread.

Bhaski

Adding to earlier reply

The 850-700 hPa meaning the top of the aerosol layer. In some instances there is aerosol above this level as evidenced from Lidar

Bhaski

Maybe you can help me out to what level the BC could rise in (pre) monsoon conditions

Harry

Because of the extremely small sizes of BC particles, it can indeed persist and fight the gravity effect longer that particles larger than 5 micron, however, because of the tropopause barrier, very few particles can go into the stratosphere, mainly with the help of few rare events such as volcanic eruptions or meteorite impacts

Tareq

In volcanic eruptions it is the SO2 that gets into the stratorpshere and it there forms sulphuric acid

Another issue is nuclea winter with ver large covective storms, see Crutzen et al.

http://web.pdx.edu/~nauna/week4a-radiometricnormalizationversion2.pdf

https://www.gfdl.noaa.gov/bibliography/related_files/sgp9901.pdf

Smog is another example of a secondary aerosol formed as a result of chemical reactions in the lower part of the atmosphere, less than 5km above the ground. Smog is a combination of airborne particulate matter such as soot, and invisible toxic gases including ozone, carbon monoxide and sulfur dioxide. Although some of these compounds such as carbon monoxide are emitted directly from vehicle emissions, ground level ozone is formed in the air from nitrogen oxide emissions. Surface level ozone (unlike stratospheric ozone which protects the surface from harmful solar rays) is hazardous to human health. Both primary and secondary aerosols have either natural or anthropogenic sources, or a combination of both.