Distribution of lead in relation to size of airborne particulate matter in Islamabad, Pakistan. 
Airborne particulate matter (PM) collected from two sampling stations in Islamabad, Pakistan, was analyzed for lead content and size gradation.  A high volume air sampler was used to trap particulates on glass fiber filters for 8-12 h on a daily basis.  Lead was estimated using a nitric acid digestion based AAS method on 44 samples from station 1 and 61 samples from station 2.  Particle size fractions were categorized as <2.5, 2.5-10, 10-100 and >100 microm.  The correlation between lead concentration and particle size was investigated.  The results from two stations indicated average airborne lead concentrations of 0.505 and 0.185 microg/m3.  Enhanced levels of lead were measured at a maximum of 4.075 microg/m3 at station 1 and 4.000 microg/m3 at station 2.  PM < 2.5 and PM > 100 were found to constitute the local atmosphere in comparable proportions.  A comparison of the lead levels is made with the existing permissible levels of this element laid down by different international agencies.