The June 2017 issue of the ASHRAE Journal features an article on measurement of indoor airborne particulate matter. The article cautions against comparing real-time nephelometric measurements of particulate matter to USEPA National Ambient Air Quality Standards for particulate matter or OSHA standards.
Nephelometers detect particles and measure light scattering by the particle. A mass concentration estimate can be obtained based on assumptions about optical properties and density. Real-time multi-fraction particle counters can be useful in refining building assessments beyond the use of CO2 concentrations as an indicator of ventilation. Although there are no health-based guidelines for PM limits using real-time count concentration values, comparing indoor results to outdoor results or assessing spaces over time can provide "practical, inexpensive guidance on managing the PM burden in a space" (p. 86). Fine particles have been associated with cardiovascular disease while coarse particles have been associated with respiratory disease, although there is an overlap in effects.