Determination of total and lung-deposited particle surface area concentrations, in central Athens, Greece

Numerous health studies have linked the exposure to particulate matter with adverse health effects, while there is an increasing scientific interest in the particle metrics of surface area (SA) and lung-deposited SA (LDSA) concentration. In the present study, two integrated SA estimation methods, both based on widely used instrumentation, were applied at an urban traffic environment in Athens for a 6-month period. The first estimation method used the size distribution by number to estimate SA (average SA₁ 669.3 ± 229.0 μm² cm^-3), while the second method used a simple inversion scheme that incorporates number and mass concentrations (average SA₂ 1627.9 ± 562.8 μm² cm^-3). In pairwise comparisons, SA₂ levels were found two times greater than the corresponding SA₁, but exhibited a strong correlation (r = 0.73). SA₁ and SA₂ concentrations correlated well with the traffic-related pollutants NO_x (r = 0.64 and 0.78) and equivalent black carbon (r = 0.53 and 0.51). The diurnal variation of SA₁ concentrations by size range indicated traffic as a major controlling factor. Estimated LDSA (53.9 μm² cm^-3 on average) concentrations were also clearly affected by anthropogenic emissions with more pronounced associations in the 0.01-0.4 μm range (r = 0.66 with NO_x and r = 0.65 with equivalent black carbon). Validating estimated LDSA through simultaneous measurements with a reference instrument revealed that the estimation method underestimates LDSA by a factor between 2 and 3, exhibiting, however, a high correlation (r = 0.79). Overall, the performance of estimation methods appear satisfactory and indicate that a trustworthy assessment of the temporal variability of SA and LDSA concentration metrics can be provided in real time, on the basis of relatively lower-cost instrumentation, especially in view of recent advances in particle sensing technologies.