SHANGHAI'S air quality improved over the first four months of the year, and the environment authority is taking further measures to build on that progress, including hitting polluters with stiffer fines, the city environment chief said yesterday.

Over the first four months of the year, the air quality was rated as good or excellent 71.9 percent of the time, a 9.4 percent increase over the same period last year.

Also, the average density of the city's major air pollutant, tiny particle PM2.5, was 58 micrograms per cubic meter from January to April, a 7.9 percent decrease over last year.