In measuring air pollutants measuring methods based on optics are often used.

Part of the pollutants in the air are precipitated with the rainwater or the snow bound to raindrops or snowflakes. Many of these pollutants change the surface tension of the water compared to pure water. The observations show that e. g. the surface tension of rainwater or water melted from snow deviates even significantly from the surface tension of pure water. In addition it has been observed that the surface tension of water melted from snow varies depending on the place and time of the sample taking. The surface tension of pure water is a natural constant, approximately 72,8 mN/m. For the surface tension of melted newly fallen snow has been measured in the center of Helsinki 48,6... 56,8 mN/m and in Vuokatti 72,3 mN/m. The difference in the measured surface tension is most obviously due to the pollutants bound to the snow. For old snow has been measured in Lintuvaara, Espoo 70,2 mN/m. In Kajaani aside the railway has been measured for old snow a surface tension of 46,5 mN/m. For comparison, the value measured for drinking water of Helsinki is 72,6 mN/m.

The lowering of the surface tension shows that the sample either has organic solvents or surfactants. The effect of organic solvents can be excluded in the samples of melted snow because the lowered values mentioned above would require high concentrations of organic solvents.

In US patent publication 3,780,569 is disclosed that the pollution of waters could be measured with a tensiometer disclosed in the publication and that the pollution could be verified by comparing the surface tension measured from the sample to the surface tension of pure water. In the publication are detergents and oils mentioned as

substances changing the surface tension. The measured value includes both the change in the surface tension due to the precipitations and the change in the surface tension caused by the substances ending up to water from the soil.

In another US publication 3,990,293 a method and apparatus is disclosed for detecting the change in the surface tension of a liquid. In this invention inert gas under pressure is fed to the water sample. When the mixture of the water and the gas is decompressed, bubbles which generate sounds are provided. In the method the intensity of the generated sounds is measured. If the water contains substances which change its surface tension, the method can also be used for monitoring pollutants in the water.

Still in the EP publication 0 653 634 is disclosed a device in which the rising velocity of gas bubbles in a water column containing water to be measured is compared to a water column containing pure water. The surfactants in the water bring about the difference in the rising velocity of the gas bubbles.

For the measurement of the density of sodium ions born by the atmosphere a device has been disclosed in the publication US 4,600,888 in which device the air to be measured is brought into contact with pure water in an open container and after that the conductivity of the water is measured. For small concentrations the density of the sodium ions can be measured with a sodium ion electrode meter. The said meter can separate sodium ions from other ions, SO2 and Nox among others.

In publication US 5,048,331 is disclosed a monitoring system for rainwater in which the pH-value and other ion chemical characteristics of the rainwater are measured.

The devices known from the publications mentioned above are intended to be used mainly in laboratories.

It is characterizing to the method according to the invention that for measuring the air pollution the surface tension of rainwater or water melted from snow or from

another solid state of the water is measured. In the following description the word snow is used for all such solid states of water like ice, snow, hails etc. In a preferred embodiment of the invention the measurement is performed as a continuous measurement during the rain by diverting rainwater to the measurement device and the measured results are stored in memory means in the measurement device or connected to the measurement device and/or the measured results are transmitted to a monitoring point by using suitable methods for data transfer. In another preferred embodiment of the invention for determining air pollutants snow is continuously collected during the snowfall, collected snow is melted preferably e. g. by means of suitable melting means connected to the measurement device and the water melted from snow is diverted to the measurement device for measuring its surface tension and for determining the air pollutants by means of the measured surface tension.

Still in a preferred embodiment of the method according to the invention one or more samples are taken during the rain, the surface tension of which samples is measured for determining the air pollutants. Correspondingly samples can be taken during snowfall from the falling snow and the surface tension of water melted from these samples is measured. In a preferred embodiment of the invention samples are also taken from the snow during the time between the snowfalls whereby by measuring the surface tension of the water melted from these samples the precipitation of the air pollutants and/or the changes in precipitations can be determined.

It is characterizing to the device according to the invention that the collected rainwater or the water melted from the collected snow is diverted to a measuring space of a measuring device in which space a sensor of the measuring device for surface tension is adapted. The surface tension of the liquid, rainwater or water melted from snow to be measured can be measured during the rainfall as a continuous measurement. In a preferred embodiment of the invention the device is provided with means for cleaning the measurement space and the sensor. The measurement space and the sensor can be cleaned after the measurement or after the rainfall. In another preferred embodiment of the invention the measurement is performed at certain time intervals during the rain and the measurement space and

the sensor are cleaned between the measurements. In a preferred embodiment of the invention the surface tension of the collected samples is measured with the measuring device for determining the air pollutants. The samples can be taken preferably with means in the measuring device. Also samples of water, rainwater or snow taken in other ways can be measured with the measuring device The measurement device is in a preferred embodiment of the invention provided with display means for a continuous display of the measurement results and/or means for storing the measured results in the memory means of the measuring device and means for processing the measurement results.

The measuring device is provided in a preferred embodiment of the invention with means for measuring the temperature of the liquid during the measurement of the surface tension and with means for transmitting the measured results to means in the measurement device or to means connected to it for processing the measured result.

In another preferred embodiment of the invention to the measurement device are connected means for measuring the amount of rainfall and means for transmitting the measured result to means in the measurement device or to means connected to it for processing the measured result. The measuring device can also be provided with means for measuring the temperature of the open air whereby in a preferred embodiment of the invention the temperature of the open air can be used e. g. for controlling the melting means. The said display means can also present the temperature measured with the temperature measurement means and/or the measured amount of rainfall, which both or of which one can in a preferred embodiment of the invention be stored in the storing means of the measuring device and can be used in the computational processing of the measured results, preferably e. g. in compensating the effect of the temperature. The measured values or some of those can in a preferred embodiment of the invention be transmitted with suitable data transfer methods and devices to desired monitoring places preferably e. g. for continuous monitoring of air pollutants.

In a preferred embodiment of the device according to the invention the measuring device has been made small in size, lightweight and preferably accumulator or battery operated, whereby it is easily transferable and is adapted for use in measurements in terrain. Further the measuring device can be made in a preferred embodiment of the invention adapted to unoccupied use in monitoring points in the terrain.

In the following the invention is described in more detail by referencing to drawings, in which Fig. 1 shows the principal scheme of the device according to the invention.

In Fig. 1 with reference number 1 is referenced the collecting means e. g. in the form of a funnel for collecting rain or snow like in meters for rainfall known as such.

These collecting means comprise in a preferred embodiment of the invention melting means 2 which is e. g. a heating resistor with its controlling and sensing means. The melting means comprise in a preferred embodiment of the invention sensing means for air temperature. The rainwater fallen into the funnel 1 or the snow melted with the melting means 2 is diverted from the funnel to a tank 3 and from there further to a measuring chamber 4. A sensor 5 of a surface tension measuring device 6 is adapted to extend to the measurement chamber 4 into the water diverted thereto from the tank 3. With the reference number 7 are shown the controlling means of the measuring device which in a preferred embodiment of the invention comprise e. g. means for controlling the operation of the measuring device, display means for displaying the measured results, memory means for storing the measured result, and calculating means for processing the measured results. The controlling means 7 are preferably in connection to the melting means 2. The controlling means 7 control preferably also means 11,12,13,14, and 15 which are preferably valves or other means adapted for controlling water. With a valve 12 between the tank 3 and the measuring chamber 4 the water accumulated in the tank 3 is admitted to the measuring chamber 4. The valve 12 is continuously open if the measurement is desired to be performed continuously. From the measuring chamber 4 the water is

diverted away by means of a valve 13. In a preferred embodiment of the invention the controlling means 7 control the valve 13 and the controlling means connected to it in such a way that in the measuring chamber 4 is always provided with a sufficient amount of water when measurements are performed. In a preferred embodiment of the invention the valve 13 is e. g. an overflow pipe. For cleaning the measuring chamber 4 and the sensor 5 pure water 16 is directed to the measuring chamber 4 with the valve 14 e. g. by means of suitable nozzles. When cleaning the measuring chamber the valve 13 is preferably controlled into an open position. The cleaning of the measuring chamber is controlled preferably with controlling means 7. The corresponding cleaning arrangement is in a preferred embodiment of the invention accomplished also in the tank 3 by using a valve 15 and pure water 10. The cleaning of the tank 3 can be controlled preferably with controlling means 7. The tank 3 can be emptied on demand with a valve 11 which is controlled preferably with controlling means 7.

The operation of the measuring device can in a preferred embodiment of the invention be automated. In this embodiment the measuring device comprises in addition to the means illustrated in the diagram e. g. means which sense the beginning and the ending of a rainfall which means together with controlling means 7 can control the cleaning of the tank 3 of the measuring device, the measuring chamber 4, and the sensor 5. Preferably after the beginning of the rainfall before starting of the measurement both the tank 3 and the measuring chamber 4 and the sensor 5 are cleaned. Correspondingly the cleaning can be performed after the ending of the rainfall.

In a preferred embodiment of the invention the tank 3 can function as the measuring chamber. Such a measuring device has naturally not means 12, means 11 and 13 are combined into one valve, preferably to an overflow pipe. From such a simplified measuring device can also be omitted the means 14 and 15for cleaning, and the feed 10 and 16 of the pure water.

Still in a preferred embodiment of the invention through the valve 15 pure water 10 can be directed to the tank 3 and by steering the valve 12 suitably open further to the measuring chamber 4 and from there through the valve 13 away from the measuring device. In this preferred embodiment of the invention the precipitations from the atmosphere can be measured also in other times than during rainfall. In a preferred embodiment of the invention the measuring device comprises means which sense the beginning and the ending of the rainfall and which are in connection with the controlling means 7 of the measuring device and with means for storing and computing therein for processing the measured results. The beginning and the ending of the rainfall and/or the data given by the measuring means for the amount of the rain can be utilized in processing the measured data of the measuring device and/or in interpreting them.

In a preferred embodiment of the invention the surface tension of the water in the measuring chamber 4 is measured preferably continuously during the cleaning and the cleaning is controlled based on this measured result e. g. in such a way that the cleaning is terminated when the measured surface tension has reached the predetermined value.