TIANJIN - Authorities in north China's port city of Tianjin on Monday said they will start including the stricter PM2.5 index in air quality readings.

Data released from the city's four air quality monitoring stations will include PM2.5, an air quality index that accounts for particles of 2.5 microns or less in diameter, starting next month, the city's environmental protection bureau said in a statement.

The number of monitoring stations is expected to be increased to 13 by the end of the year and 27 by next February, according to the statement.

To make the air cleaner, the bureau said it will raise environmental thresholds for new enterprises, order more boilers to be powered by gas instead of coal and restrict the number of cars on the city's roads.

The State Council, or China's cabinet, passed a new air quality standard that included an index for PM2.5 on February 29. The standard will be implemented in major cities in 2012 and 2013 before covering the whole country starting in 2016.

Beijing led other cities nationwide in releasing PM2.5 readings in January following public outcry over the inaccuracy of PM10 readings. Fine particles of 2.5 microns or less are believed to pose greater health risks than larger particles.