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Time and size resolved indoor/outdoor particles in an empty room

Lazaridis Michalis, Hollander,W, Zdimal, V, Smolik ,J

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Summary

Finding the concentration Cin of a non-reacting pollutant in a room of volume V is the main objective of indoor air modeling. Cin is controlled by the ventilation rate of indoor and outdoor air (with concentration Cout), sources Q, and sinks S. Here we measured time and size resolved indoor and outdoor particle concentrations and compared the experimental results with the prediction based on simple mass balance model. MODELLING OF INDOOR PARTICLE CONCENTRATIONS The temporal evolution of the indoor concentration including contaminant sources and sinks can be under well mixed conditions described by the first-order linear differential equation dCin/dt = ? (Cout - Cin) + q (1) Here q = (Q-S)/V is combined sources and sinks term divided by the room volume. For constant ?, Cout, and q and for the initial condition Cin = Cin (0), the equation (1) has the solution Cin = e-?t Cin (0) + (1 - e-?t ) (q/? + Cout ) (2) As can be seen the solution has a decay following a single time exponent ?. After infinitely long time the equation (2) has the stationary limit Cin (?) Š q/? + Cout (3) RESULTS Indoor and outdoor particle size measurements were made using two Scanning Mobility Particle Sizers (SMPS) model 3936N25 and 3934C, and Aerodynamic Particle Sizer (APS) model 3320. The instruments covered particle size range from 3 nm to 20 microm. The same instruments were used for sampling both indoor and outdoor aerosol using valve system that allowed the aerosol samples to be drawn in alternating time periods from inside and outside the room. The measurements were conducted in an empty office (without any furniture and any activity inside) and outside the window. To prevent possible generation of aerosol by the measuring system all the instruments and pumps were located in a room different from the office where the air samples were taken. Usually three 5 min sampling cycles for indoor sampling followed by three cycles for outdoor sampling were used. The measurements were corrected for multiple charging, efficiency of CPC counters, and particle losses in sampling trains. To observe the dynamics of the process the office was equilibrated from time to time during the measurements with the outside environment. For this purpose the windows of the office were opened for about 2 hours to exchange air between the office and surroundings.

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