Ambient levels of lead (Pb) in PM10 were studied at a site in Central Delhi for the period of one year during day and night. The annual mean concentration of lead has been observed as 625 and 1051？ng/m3 during day and night time, respectively. The seasonal averaged concentrations of Pb have followed the order winter > postmonsoon > summer > monsoon. Highest levels of lead have been observed in winter with 31% samples exceeding the CPCB-NAAQS value as 1000？ng/m3. Lead levels during winter have been found to be 5.7 times higher than in monsoon, which might be attributed to prevailing meteorological conditions and more biomass burning. The low levels of Pb during summer might be attributed to its higher dispersion in the atmosphere. A sharp rise of Pb during postmonsoon might be linked to the local nonpoint sources, more biomass burning, and shifting of boundary layer. However, the higher concentrations of lead were observed during night time in all the seasons of the year as compared to those of the day time. To identify the potential source regions of Pb, Concentration Weighted Trajectories (CWT) have been plotted which showed higher influence of local sources during winter and postmonsoon while showing distant sources during summer. 1. Introduction Among the various air pollutants, particulate matter plays an important role due to its effects on different atmospheric processes such as visibility, atmospheric chemistry, radiative balance, and human health [1, 2]. Trace metals associated with particulate matter may increase manyfold, by natural or anthropogenic sources [3–5]. At elevated concentrations, certain trace metals (Hg, Pb, Sn, Cd, etc.) show toxic effects on living beings [2, 6, 7]. Lead (Pb), as a well-known neurotoxin, shows high level of toxicity on living beings [2] and is the only metal listed in the EPA-NAAQS (http://www.epa.gov/air/criteria.html). Due to its adverse effects on human health, especially on pregnant women and children’s growth and intelligence, study of Pb has been a topic of interest. Anthropogenic activities play a major role for the emission of lead into the atmosphere [8]. Once it enters into the atmosphere, it can be deposited on the surface and resuspended to reenter the atmosphere. Thus, it has high potential to remain in the environment [9, 10]. This could increase human exposure to Pb causing adverse health effects [11]. Lead is released into the atmosphere mainly in the gaseous form during high temperature anthropogenic processes such as metal processing, fuel combustion, nonferrous metal production, or waste
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