The monitoring of PM2.5 is done with manual monitoring or automatic monitoring. Data collected from these two methods is systematically different from each other, and must be harmonized and calibrated through comparison and statistical analysis to ensure consistency. According to the statutory air quality standards, the data collected through standard manual monitoring should prevail when monitoring PM2.5.
To make sure that the data collected from automatic monitoring and manual monitoring can be more consistent, we refer to the practice of the Environmental Protection Agency of the United States and developed a linear regression (relation) equation to calibrate data collected by automatic monitoring and publish them in real-time, which can serve as an early warning. The calibration of data began in May 2014 and started with data from January 2014.
The EPA planned to replace old PM2.5 automatic monitors starting from 2019. It is now comparing the new and old instruments batch by batch. In order to understand the differences in functions of the new and old instruments and avoid changing the linear regression equation lest adding confusion to data comparison, the "national linear regression (relation) equation for automatic monitoring of fine particulate matter (PM2.5) in 2017" continue to be effective without any change.
New instruments have passed tests related to regulations governing the comparison between data collected from instruments and data collected from manual monitoring. Therefore stations that has replaced their instruments do not need to calibrate the equation.
Stations that have replaced old instruments with the new ones (date of replacement): Linyuan (Oct. 23, 2018), Guting (Nov. 22, 2018), Xinying (Oct. 11, 2018), Chiaotou (Nov. 23, 2018), Lunbei (Jan. 1, 2019).
The PM2.5 value collected from automatic monitoring and calibrated based on the relation equation is meant for the convenience of a comparison with the data value collected from manual monitoring. If it needs to be compared with automatic monitoring data of PM10 or an analysis of the proportion of these two particulates must be done, the differences between manual monitoring and automatic monitoring must be considered. It is suggested that the relation equation can be used reversely so to get the automatic monitoring data of PM2.5 or just use the original monitoring value.
The PM2.5 value of manual monitoring is collected by applying a standard monitoring method to take samples for 24 consecutive hours.
A total of 31 manual monitoring stations is installed around the country. Since the setting and collection of samplers is done manually, it can only be done once every 3 days, and another 20 days are needed for preparation, measurement, and processing for quality assurance and quality control. In addition, because Taoyuan County had become a municipality, 1 station was added in Pingzhen District starting from January 12, 2015.