Analysis and interpretation of particulate matter – PM10, PM2.5 and PM1 emissions from the heterogeneous traffic near an urban roadway

This paper presents analysis and interpretation of diurnal, weekly and seasonal cycles of 1–h average particulate matter (PM10, PM2.5 and PM1) concentrations measured near an urban roadway in Chennai city, India, between November 2007 and May 2008. The PM data analysis showed clear diurnal, weekly and seasonal cycles at the study site. In diurnal cycle, highest PM concentrations were observed during weekday’s peak hour traffic and lowest PM concentrations were found during trickle traffic (afternoon and nighttime). The seasonal PM data analysis showed highest concentrations during post monsoon season (PM10 = 189, PM2.5 = 84, PM1 = 66 μg/m3) compared to winter (PM10 = 135, PM2.5 = 73, PM1 = 59 μg/m3) and summer (PM10 = 102, PM2.5 = 50, PM1 = 34 μg/m3) seasons. The particle size distribution during post-monsoon, winter and summer seasons showed two distinct modes viz. accumulation (mean diameter, d = 2.2 μm; distribution = 40%) and coarse (d = 7.1 μm, distribution = 60%). The frequency distribution of PM10 concentrations during post–monsoon and winter seasons indicated that the PM10 values at the study site fall under moderate to poor categories. During post–monsoon and winter seasons, it was found that more than 50% of the time the 24–h average PM10 concentrations were violating the Indian national ambient air quality standards (NAAQS) (100 μg/m3) and world health organization (WHO) standard (50 μg/m3). The 24–h average PM2.5 concentrations were also exceeding the NAAQS (60 μg/m3) and WHO standards (25 μg/m3) by 75% of time, irrespective of seasons.