Evolution of PM_2.5 measurements and standards in the U.S. And future perspectives for China

National Ambient Air Quality Standards (NAAQS) were first established in the United States to protect public health and welfare, and the concept has been adopted in China and many other countries. For particulate matter (PM), the NAAQS indicator evolved from total particle mass concentration, to PM₁₀ and PM_2.5 mass concentrations as defined by the PM size-selective properties of the monitoring instrument and human inhalation characteristics. Particle measurements started with optical microscopy in the early 18^th century, and scientific research over the past 300 years has related particles to adverse environmental and health effects. Several options for PM_2.5 measurement and assessment are available to China and other developing countries as they implement new PM_2.5 ambient air quality standards. Although much can be learned from the experience of North America and Europe, China can leapfrog ahead in terms of PM_2.5 monitoring and emission reduction technology. China-specific guidance documents should be created for network design, equipment selection and operation, quality control and quality assurance, database management, and interpretation. Future air quality management and standards will need to consider multiple pollutants and their effects on visibility, climate, materials, and ecosystems in addition to the primary concerns about public health.