by Emily Segal
Particulate Matter (PM) is an air pollutant that when large enough can be seen as soot or smoke, and when small enough, can only be observed using an electron microscope. Particles less than 2.5 micrometers in diameter (PM2.5) are especially dangerous because they can be inhaled into the respiratory system and can lodge in the lungs. Scientists have been studying the quantity of particulate matter in the air for a while, but between 1988 and 2013, the system for monitoring this air pollutant underwent many changes. Essentially, the old way of measuring PM2.5, through traditional filter sampling, was replaced by the more effective method of using Beta Attenuation Monitors (BAM). It is important to have a monitoring network that operates frequently and in many areas because this data can then be compared to data from various hospitals in order to draw conclusions about the connections between PM2.5 concentrations and health consequences. Additionally, the real-time nature of BAM can help make short-term forecasts for air qualities in different regions. This was not possible previously because traditional filter sampling had many delays caused by transporting, conditioning, and weighting filters before any conclusions about the actual PM2.5 measurement could be made.
In their paper entitled “Changes in fine particulate matter measurement methods and ambient concentrations in California,” Ling Tao and Robert A. Harley analyzed the available record of filter-based and BAM measurements of PM2.5 concentrations in California. There was much more PM2.5 data available from BAM then from filter measurements which they found were often checked once every third or sixth day or had missing samples all together. For example, in 2013, records showed that in the San Joaquin Valley, an average of 89% of days had BAM data compared to only 38% of days that had data from filter-based methods. Tao and Harley concluded that overall, PM2.5 levels in California have been reduced greatly over the last two decades. Especially in Los Angeles, the amount of PM2.5 in the air decreased by 50% between 1988 and 2013.
Tao, L., Harley, R., 2014. Changes in fine particulate matter measurement methods and ambient concentrations in California. Atmospheric Environment 98, December 2014, Pages 676–684.