Volatilization of PAHs from sealcoated pavement Peter C. Van Metre, Barbara J. Mahler, William Foreman, Christopher Braun, Jennifer Wilson, Teresa Burbank, and Rhiannon ReVello
Mean PAH in six coal-tar based products (dried 3 days indoors) is ~90,000 mg/kg 1 Mean PAH in 12 scraping samples from coal-tar sealed lots is ~20,000 mg/kg 1,2 PAHs in fresh and aged sealcoat 1 Mahler et al., Van Metre et al., 2009
PATHWAYS
Ambient Air Surface air layer Impervious surface K sa =C surf /C hat,eq F(T°) Hat sampling 1 Gradient: source or sink? 1.28 m 0.03 m 1 Meijer et al., 2003
In-use parking lots Ten in use parking lots in Austin, TX. Seven with sealcoat, three unsealed pavement Summer 4 pm samples at all sites, 4 am samples at five Pavement dust sampled
Pickle Test Plot Newly CT sealed test plot at UT Pickle Research Campus Sampled for 1 year: 2 hours after sealing, then after 1, 5, 16, 45, 149, 232, 328, 373 d Monitored wind and temperature Collected pavement dust and scraping samples at each time
Analysis PUFs were ASE extracted and PAH analyzed by GC/MS 19 PAH quantified 8 PAH frequently detected: Phe, An, 4,5- MP, 1-MP, Flu, Py, Chy, and B(b)F
The Solid Phase PAH 8 in dust at in-use lots Coal-tar sealed (n=6) 1,200 – 7,100 mg/kg Asphalt sealed (n=1) 29 mg/kg Unsealed (n=3) 0.47 – 6.3 mg/kg PAH 8 at Pickle Dust (n=2) 2,500 & 1,400 mg/kg Scrapings (n=4) 11,000 – 28,000 mg/kg
PAH in Air PAH 8 in unsealed lots HAT = 73 AMB = 26 ng/m 3 dC/dz Phe = 17 ng/m PAH 8 in sealcoated lots HAT=1,770 AMB = 190 ng/m 3 dC/dz Phe = 466 ng/m
Source/Sink?
Surface source
PAH Pickle test plot PAH 8 2 hours after application HAT = 290,000 AMB = 5,400 ng/m 3 dC/dz Phe = 165,000 ng/m PAH days after (during winter) HAT=291 AMB = 28 ng/m 3 dC/dz Phe = ° C 34° 41° 31° 17° 11° 31°
PAH Pickle test plot R 2 = 0.95 t 1/2 = 7 days
Fluxes? Q = u* K T [C a (z hat ) - C a (z amb )] (1) Q = flux [C – C] = air concentration gradient u* K T = mass transfer coefficient (1) Scholtz et al., 2002 u* KT is primarily a function of wind speed
Flux = f (gradient)