Supplemental Material

Development and Characterization of an Exposure Generation System to Investigate the Health Effects of Particles from Fresh and Aged Traffic Emissions

Vasileios Papapostolou, Joy E. Lawrence, Stephen T. Ferguson, Jack M. Wolfson, Edgar A. Diaz, John J. Godleski and Petros Koutrakis

1. Lamps irradiation rate

The light irradiation of the combined UVA-350nm and UVB-313nm lamps in the chamber was estimated by determining the nitrogen dioxide (NO2) photolysis rate (j1) in the chamber. A mixture of nitric oxide (NO) and O3 in clean, particle-free air was introduced continuously into the chamber at a total flow of 35 L/min. When a stable NO2 concentration was reached, the lamps were turned on. After 2 chamber mean residence times, the NO2 photolysis rate (j1) was calculated using the photostationary state relationship (Cocker et al. 2001; Seinfeld and Pandis 2006) of NO, NO2, and O3 (Equation 1):

[1]

where k2, the temperature-dependent rate constant for the reaction of NO and O3, has a value (T in degrees K) (Seinfeld and Pandis 2006). We estimated the NO2 photolysis rate to be j1 = 0.41 min-1, which is comparable with those reported by other researchers. For example, Zafonte et al. (1977) measured j1 = 0.45 min-1 in Los Angeles at noon time. The maximum NO2 photolysis rate observed at ground level (at mid-US latitudes) on a clear day with direct overhead sunlight is approximately j1 = 0.3 min-1 (Carter et al. 1995). Thus, the light intensity in the photochemical chamber is reasonably representative of sunlight.

2.  Secondary aerosol composition

Supplemental Material, Table 1. SOA composition diagnostic ratios

P+SOA / SOA
Baseline / Plus O3 / Lamps / Baseline / Plus O3 / Lamps
EC/PM / 0.26 / 0.20 / 0.05 / 0.00 / 0.00 / 0.00
OC/PM / 0.24 / 0.71 / 0.39 / 7.28 / 2.31 / 0.23
OC/EC / 0.93 / 3.62 / 7.35 / N/A / N/A / N/A
OC1/OC / 0.03 / 0.01 / 0.01 / 0.01 / 0.03 / 0.01
OC2/OC / 0.50 / 0.48 / 0.29 / 0.50 / 0.46 / 0.30
OC3/OC / 0.39 / 0.36 / 0.38 / 0.29 / 0.30 / 0.37
Pyrol C/OC / 0.00 / 0.04 / 0.19 / 0.12 / 0.13 / 0.21
(NH4)2SO4/EC / 0.30 / 0.41 / 3.33 / N/A / N/A / N/A
NH4NO3/(NH4)2SO4 / 0.66 / 2.88 / 0.68 / 0.91 / 6.75 / 0.54

References

Carter WPL, Luo D, Malkina IL, Pierce JA. 1995. Environmental chamber studies of atmospheric reactivities of volatile organic compounds. Effects of varying chamber and light source. Final Report.

Cocker DR, Flagan RC, Seinfeld JH. 2001. State-of-the-art chamber facility for studying atmospheric aerosol chemistry. Environ Sci Technol 35:2594-2601.

Seinfeld JH and Pandis SN. 2006. Atmospheric chemistry and physics: From air pollution to climate change. New York: John Wiley and Sons.

Zafonte L, Rieer PL, Holmes Jr. 1977. Nitrogen-dioxide photolysis in Los Angeles atmosphere. Environ Sci Technol 11:483-487.

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