Traffic exhausts, especially from diesel engines, contain large numbers of fine particles and these can be hazardous to health because they can be breathed directly into the lungs where they aggravate the lung tissue. Their presence can be measured either in the air in the street (the ambient air) or close to a vehicle.

Procedure for measuring particulates in ambient air

This experiment should be carried out on a dry, calm day. Select your measuring site which can be on a window ledge or close by a street. You may need an electrical extension lead if your monitoring site is well away from a power point. Plug in a small vacuum pump - a suitable pump will be an aquarium pump but using the suction end - and connect it to a filter funnel onto which you have placed a circle of dampened filter paper. Switch on the pump and let it run for a predetermined period of time, say one hour. Disconnect the pump and examine the filter paper for accumulated particles. If this procedure is followed in a number of different locations, such as indoors and outdoors, or town and country areas, you can compare the intensity of the colour of the filter papers as a measure of air quality as long as you use the same period of time for suction.

Procedure for measuring particulates in a vehicle exhaust Another experiment to carry out is to check on the emissions from individual vehicles. You will be aware of government plans to improve air quality by persuading us that we should use our cars less. One problem in towns and cities is that there is so much traffic, that the vehicles spend a lot of time stationary with their engines running. This produces polluting gases and particulates.

In this procedure, you will be able to assess the amount of particulates that are emitted from a stationary vehicle. You will need:

An electrical extension cable

A vacuum cleaner (a cylinder type or one with a hose attachment)

A piece of filter paper large enough to be fitted over the end of the suction hose and secured with an elastic band

The vehicle to be tested is parked in a convenient position in the open air (do not do this experiment in a confined space like a garage) close to where the vacuum cleaner is connected to the extension cable. Have the owner start the vehicle and let it idle in neutral gear. Switch on the vacuum cleaner and, standing beside the vehicle, direct the hose with its attached piece of filter paper so that it is about half a metre beyond the end of the exhaust pipe. Suck in the exhaust gases for about 10 minutes, have the engine switched off and then disconnect the vacuum cleaner. Examine the colour of the filter paper and compare it with another piece that has been used to suck air without the vehicle present.

Using this technique, you can compare the results for different vehi cles or else the same vehicle before and after the engine has warmed up. You are probably aware that, on cold winter days, a vehicle may have reached its destination (if it's a short journey) before the engine has warmed up and so the pollution levels are greater in winter.

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