ECAC - Forum

Hi all,

as Hohenpeißenberg station is in clouds/fog for >5-10% of the time (~10% with visual range <200m) we are supposed to change our current PM10 inlet (installed 2003, DIGITEL, 170 l/min) to whole-air. In order to minimize rupture of time series (as of 1995) and pollution of instruments by pollen, local dust, plant debris..., we think about possible modification of the standard PM10 inlet (http://www.digitel-ag.com/de/en/product ... lets/pm10/) to fulfill 'whole-air inlet' criteria, e.g. by elongating and heating the outer cover/cylinder or something similar.
Has anyone experience with such a modification, knows about from-the-shelf solutions to this, or expects this to be no promising approach because of reasons we have not yet thought of?

Thanks & cheers,
Harald

Hi Harald, I believe that the dimensions of a common PM10 inlet are not appropiate for a high sampling efficiency of cloud droplets to get them into the warm evaporation zone. One needs a minimum stopping distance, which can be calculated, assuming the maximum droplet diameter and maximum horizontal wind speed. The stopping distance will be certainly few centimeters.

Hi Harald,
just to put it in other words, the idea of the whole air inlet is to catch and measure also those aerosol particles that were activated into cloud droplets. If the cloud droplet size distribution extends over 10um (as it very often does), then a PM10 inlet would cut out these droplets and miss the particles in those droplets as well.

We experience a similar break in our optical data at Pallas (GAW PM10-> ACTRIS whole air inlet change), our approach was to make parallel measurements from PM10 and whole air inlet for a few months. That should help to homogenize the long term data series later on.

Thank you for your answers 1.5 years ago!

Meanwhile for Hohenpeissenberg we plan with TROPOS to implement an inlet train whole-air + subsequent PM10, which should, at least in theory, impose no break to our time series for the data fraction taken under 'no fog' conditions and save us much cleaning efforts.

So Antti, did you perform the parallel measurements PM10 and whole-air inlet? And if so did you observe any differences under 'no fog' conditions? Did you suffer from increased instrument pollution or gradual contamination by particles larger 10 µm - pollen, insects etc?