Sensors for air quality

Air quality is certainly more regulated than it used to be back in the day, especially in California 

The Government has established regulations for monitoring air quality and defining what acceptable levels of pollution are.  There are several measurements required by the EPA and other organizations (such as the California Air Resources Board):

PM2.5:     Fine particles less than 2.5micron in size.  This is a very important measurement because this size particulate is what is absorbed by our lungs and so has the largest health impact on us.

PM10:     Larger particulate matter up to 10micron, less impact on human health.  (but still part of the 'haze').

Gases:    SO2, CO, O3, and NO2

Chemical Speciation:    Measures levels of metals, ions, and carbon constituents suspended in the air.  Lab analysis is performed on particulate pollution samples to find out how much is dangerous material.

PM2.5 fine particulate levels in the US are legally required to be <50 ug / cubic meter.  Parts of India, the Phillipines, China and many other places have PM2.5 levels that average more than 10 times our legal limit!!! so we can be thankful for our enforced regulations. 

Many of the sensors/monitors used in these networks cost many thousands of dollars and require a lot of technical expertise to use and to analyze the data.  I'm sure there are simpler, less expensive, and less accurate options out there for measuring many of these pollutants.