Non-heating Period Research Articles

Correlation of the atmospheric extinction coefficient with the concentration of particulate matter for measurements in a polluted urban area

Measurements of the volume extinction coefficient employing a Laser transmission path through the atmospheric boundary layer of the city of Leipzig are presented. Working conditions of a long path measurement and the calibration are discussed. To compare the extinction coefficient with other atmospheric quantities the influence of relative humidity on the extinction coefficient is eliminated by a humidity correction. The humidity corrected extinction coefficient is shown to be a measure of atmospheric loading. Based on changes of concentration of aerosol particles the results of measurements are classified in terms of heating or non-heating period and in terms of different air masses. For the empirical relation between the humidity corrected extinction coefficient and the concentration of particulate matter the specific extinction is introduced. With the help of this quantity conclusions are drawn about the shape of the size distribution of atmospheric particles.

Optimization of control systems for near-ambient grain drying: Part 1, the optimization procedure

A method was developed of finding the optimum values of up to 10 parameters defining the size of equipment for, and the method of operation of, a near-ambient drier. The optimization procedure does not need a linearization of the drying model. Initial estimates of the cost of energy and overdrying are obtained by the systematic and repeated running of the Agricultural and Food Research Council, Institute of Engineering Research (AFRC IER) near-ambient simulation program (STOREDRY) with a range of values of each of the parameters to be optimized and with weather data averaged over 20 years. After rejecting those combinations of parameters giving excessive spoilage or drying time, a selected number of the best combinations are tested and, if necessary, re-ordered by running for each individual year of the 20. New and narrower bounds within which to adjust the parameter combinations are calculated and the whole process is repeated until there is no further improvement in the best ‘score’ and an optimum combination is identified. The policy to be optimized is similar to that developed in earlier work by Ryniecki. The main features of this ‘fan-and-heater’ policy were that it allowed for the airflow to be altered between heating and non-heating periods and for the control set-point relative humidity to vary with the progress of drying.

Properties of atmospheric aerosols inverted from optical remote sensing

A new approach is proposed for optical remote sensing of atmospheric aerosols. A multiwavelength radiometer was used to measure direct solar radiation and sky radiation on the solar almucantar. The scattering phase function, the atmospheric optical depth, and their variation with wavelength were inverted simultaneously. A ‘reserve’ method was used to obtain the size distribution and refractive index of atmospheric aerosols. The results indicated that in Beijing city, the minimum total optical depth was 0.33 measured in September and October, and the maximum was 0.462 measured in March. The average value of the imaginary part of refractive index was 0.034 (0.532 μm) measured in winter (heating periods), and was only 0.016 (0.532 μm) measured in nonheating periods. A parallel observation was made to check the remote method, in which the aerosol size distribution was measured with a cascade sampler and the absorption coefficient of aerosols was obtained with the integrating plate method. The agreement of the results showed that the approach proposed was useful.