What scale of altitude are you referring to? Within a city, as most pm10 and pm2.5 are emitted by traffic i.e. close to the ground, pollution is decreasing with height. For ground emissions, the distribution might resemble a Gaussian profile. If you look at a mountianeous area, most emissions are generated in the valleys, so in that scale too, pollution is decreasing with height.

Hmm, maybe your question aims at vehicle emissions as a function of altitude. For engine emissions of opacity (as in PM10 or PM2.5), data is indicated in the 2012 PIARC report on vehicle emissions -> Table 26 on page 34. However, this is applicable only to engine emissions and not to non-exhaust particle emissions.

http://www.arnolddix.com/wp-content/uploads/2012/10/2012-Vehicle-emissions-and-air-demand-for-ventilation.pdf

Thanks for your reply. You are right, my question was about the variability of PM emissions from traffic and industrial sources in cities located > 2,000 m above sea level. I see there is poor data about that. I read the PIARC report and it is interesting to note (on Table 26) that the opacity increases by 50% from 0 m to 3,000 m. I live in a city at 2,650 m, so this increase is very significant.

Yes, the data base for vehicles at high altitude is very poor indeed. That is the reason why for various countries the altitude factor is indicated as unknown (in the PIARC report). But in the future, PM10 emissions will be more and more dominated by non-exhaust emissions (dust re-dispersion, tire and road abrasion).

Omar, take a look at this reference from Bravo et al. 

http://www.sciencedirect.com/science/article/pii/S0269749112004356

Hello Omar - one 'technical' consideration for published PM levels is verification that the PM levels were adjusted correctly to the same standard conditions for cross-comparisons.  Air volume is affected by p, T and moisture content.  Here too, some researchers define 'standard conditions' differently, and so do PM equipment manufacturers.  Something to be aware of... Good luck with your research,

Jacek

Hi Juan, I know the paper by Bravo et al. They propose correction factors to TSP and PM10, but I think there is not PM2.5 data.

Hello Jacek, thanks for your reply.

As you say, PM data should be corrected to standard conditions. I will follow the guidelines and the equations of the sampler manufacturer, which are the same as those proposed by Bravo et al. The equations consider p and T, not moisture content.

Here a paper of chemical composition and source apportionment of PM10 in a city at 2,650 m:

Article Chemical composition and source apportionment of PM10 at an ...

https://www.scidev.net/asia-pacific/pollution/news/air-pollution-decline-with-height.html?__cf_chl_jschl_tk__=ee75252cf27288205b0824195363e000191d893c-1591626345-0-AdPkpqPKSWis_Mm8rUEs_L90iSzVj3k_FDx2mV0Tw2a_VqjfjY7fMoP9BUX32bhMl6N3DiHP_mSxrr7BwZeBoo6T5rFftCW5Od3731HR54ktBweQ7Jl-HHZqHUGFWq4ufBE6qWxMZ8Oh3PTqtiJobjFwBCtn0FR_mIdDcBFR4t-lc8xibGi34Jm8zADKK3NgvBVYEmBwjipL_h6frqAiw8lFWgVHRbexIWppS2HudKP6QL2ZCZSGQ4FyTyKrJIeqAFM32QwjOXupXioYinOPKwJh8Z40aLA2zv7_iPi339_PriHnLPKbXLH8hX8FkglEPs1sbhcrbJtRa8IXyo2rJ97JSIKbmLzhUu0mCHfD7MXR