Toxicity potential of particles caused by particle-bound polycyclic aromatic hydrocarbons (PPAHs) at two roadside locations and relationship with traffic.

This study assessed exposure by the roadside to highly toxic particle-bound polycyclic aromatic hydrocarbons (PPAHs) that are known to adsorb preferentially on fine particles, aerodynamic diameter (dp ≤ 1 μm). The real-time air quality measurements were conducted in March, April, and May 2015 in Kanpur at two busy roadside locations: one outside IIT Kanpur main gate, IG, and another by a residential area, M3. The locations show varying land use type and traffic density. Higher averaged daily concentrations of PM10, PM2.5, and PM1 were observed at IG (PM10 700-800 μg/m3) owing to nature and high density of traffic, and occurrence of biomass burning nearby. Statistically significant relation (R2 > 90%, p < 0.05) between PM1 and PM2.5 highlights the influence of mobile sources on particle load at IG. IG, the busier location, had higher daily averaged concentration of aggregate PPAHs (104 ng/m3) than M3 which is located near a residential area (38 ng/m3). In contrast, the higher average daily value of PC/DC ratio (mass per unit surface area of PPAHs on nanoparticles) at M3 (4.87 ng/mm2) than at IG (4.08 ng/mm2) suggests that PAHs of greater mass occur on particles at M3. Finer particles are known to adsorb pollutants of a larger mass that are likely to be more toxic in case of PAHs suggest that ambient air at M3 has more toxicity potential. However, this inference is not based on chemical analyses, and chemical characteristics must also be taken into account for the detailed assessment of health risk. The multiple path dosimetry model (MPPD-v3.04) reveals that the 99.02% of PM10 inhaled, 77.01% of PM2.5 and 34.54% of PM1 are deposited in the outermost (head) region of the human respiratory tract.