[Stoves] Particle measurements - influence of bio-sourced aerosols in the ambient air

Crispin Pemberton-Pigott crispinpigott at gmail.com
Fri Jan 24 10:46:52 CST 2014


Dear Friends

 

I know this is a matter of limited interest but this list is the right place
to share the information.

 

The direct and indirect radiative effects of biogenic secondary

organic aerosol

http://www.atmos-chem-phys.net/14/447/2014/acp-14-447-2014.pdf

 

This paper discusses naturally occurring biogenic secondary organic

Aerosol from trees (etc) which form part of the background PM2.5. There are
two major contaminants that mess with the PM numbers measured when testing
stoves - water vapour (when the humidity is about 70%) and 'other things'
like ground-blown dust, smoke from other sources and natural haze from
(especially) trees. 

 

It cites papers works by two Stove listers Tami Bond and Harold Annegarn.

 

Some stoves are so clean that the background level dominates the readings.
Establishing what the background level is becomes very important. 

 

The condensation of water vapour is a serious issue in hood collection
systems and according to TSI (the instrument people) the effect is
significant above 70% humidity which is a lot lower than my uneducated
guess.  Using ambient air as a dilutant for PM is the main problem. If the
air has more particles in it than the stove is emitting, how can you tell
what the stove emissions are? That is the basic idea. If you are using
ambient air in a hood, the condensation of water vapour (which is not what
we want to measure) can completely overwhelm the PM emissions from the fire.

 

Stoves produce a lot of water vapour from fuel moisture and burning
hydrogen. This easily condenses and is measured as a particle by light
scattering instruments. Filters collect everything and you can dry them to
remove the moisture but will remove things that evaporate above the dilution
tunnel temperature. For example bio-aerosols that condense at 50 or 80 C
will also be removed from the filter by drying.  The question is what %
effect this has on the filter mass.  Turns out it depends on where you are:
i.e. near forests means more and a larger effect. 

 

Using a filter for end-to-end measurements means there is no real time PM
data and it is hard to know when the smoke was produced: during ignition,
during high power burning... That makes tuning a stove to super-low
emissions difficult. So you see the problem.

 

The paper above is dealing with Cloud Condensation Nuclei and growing
particles - a little arcane for stoves as it focusses on albedo, but it is
yet another paper relevant to the PM conversation.

 

Regards

Crispin

 

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