Small sensors are not always the best option for evaluating air quality. Other alternatives to consider are:

• Diffusion Tubes: Cheap fixed tubes that can give reasonably accurate monthly readings at low cost, and are very easy to site.
• Nearby Fixed Monitoring: If there is a nearby fixed monitoring site that has a similar location e.g. how far from road, and measures the species you want, then it may be much more effective to use this.
• Modelled data: Many government bodies create annual maps of air pollution based on monitored data, and these may be an easier way of finding air pollution problems.

If these are not available and sufficient then small sensors can be considered, but care must be taken to make sure the Sensor selected is suitable for the question you are asking.

Some Sensors only work well at certain concentrations or under particular circumstances. A sensor may be able to show that pollution is higher at a certain time or place, but few if any can reliably be used to see if a location has exceeded an air quality standard.