Introduction
Solid materials are part of the air besides of gaseous and liquid parts. They are natural part of the air or they are emitted into air by human activity. Solid aerosols are good powdered matters scattered in atmosphere, where they persist some time. Lifetime of particles in the air depends on their size. The particles greater than 10 um settle very fast due to gravitational force. The particles smaller than 10 um persist due to air streams in atmosphere from hours to tens of days. The particles smaller than 1 um are part of Brown's movement and sediment only if they create cluster.
Adsorption of gases is important property of solid aerosols. They can act as carrier of spores, molds and microorganisms. Many methods were developed for measurement of solid aerosols: sedimentation, filters, thermoprecipitation, elektroprecipitation and konimetric. Particles are adsorbed on glass (slide) exposed to high speed air in konimetric method. The air is accelerate by nozzle. Wet particle are adsorbed to the slide after impact. Adsorption may be supported by sticky matter on the slide. Samples give current values, so the time series may be created. There are some construction variants of konimeters (Zeiss, Busch-Lomb and Owens). Combined konimeters are known as impactors. We are exploring Owens type konimeter in our experiment. Measured air is pumped through the wet chamber and continues through the rectangular nozzle with dimensions 0,1 x 8 mm (or. 0,2 x 8mm or 0,3 x 8 mm). The speed of the air in the nozzle is significantly increased (continuity equation) and the speed of aerosol particles is increased too. Behind the nozzle is positioned slide, where the aerosol particles are adsorbing in shape of rectangular track with dimensions of the nozzle.. Scheme of konimeter is on figure 1. Number of particles on microscope slide is counted with microscope.Equipment:
Konimeter, microscope, microscope slides, tools for slides manipulation and nozzle cleaning, filter paper.Procedure:
- Check konimeter.
- Open konimeter head and clean out nozzle.
- Make clean the microscope slide and place it into konimeter head. Close the konimeter head.
- Place wet filter paper into cylinder of konimeter head.
- Pump air through the konimeter head.
- Take the slide from konimeter head and place it into microscope. Use small zoom first to locate dust track. Then change the zoom to be able count dust particles.
- Replace ocular without scale by ocular with scale. Adjust focus. Count
particles in randomly selected parts of scale. Then calculate
average number of particles between two ticks of scale (fig. 2).
Then calculate total number of particles in the track.
Parameters of oculars with scale:
one scale tick for ocular H8x and objective 20x is 0,011 mm
one scale tick for ocular P15xPo and objective 20x is 0,0063 mm - Calculate
the dust concentration using formula:
where c…average number of particles between two ticks
o…number of ticks in track
V…volume of pumped air. - Evaluate shape eventually size of particles. Guess if it is mineral or organic dust.
- Guess total weight of dust per volume unit. Presume density 2,5 gcm-3.
- Repeat measurement for more samples.
Evaluate uncertainties of measurement. Evaluate influence of meteorological conditions on dust concentration measurement.
Fig. 1
Fig. 2