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 SPAH in six coal-tar based products (dried 3 days indoors) is ~90,000 mg/kg1

Mean SPAH in 12 scraping samples from coal-tar sealed lots is ~20,000 mg/kg1,2

PAHs in fresh and aged sealcoat

PAHs in fresh and aged sealcoat

1Mahler et al., 2005 2Van Metre et al., 2009

PATHWAYS

Ambient Air

Surface air layer

Impervious surface

Ksa=Csurf/Chat,eq

F(T°)

“Hat” sampling1“Hat” sampling1

Gradient: source or sink?1.28 m

0.03 m

1Meijer 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 SPAH8 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

SPAH8 at Pickle

Dust (n=2) 2,500 & 1,400 mg/kg Scrapings (n=4) 11,000 – 28,000 mg/kg

PAH in Air SPAH8 in unsealed lots

HAT = 73 AMB = 26 ng/m3 dC/dzPhe= 17 ng/m

SPAH8 in sealcoated lots

HAT=1,770 AMB = 190 ng/m3 dC/dzPhe = 466 ng/m

Source/Sink?

Surface source

PAH Pickle test plot

SPAH8 2 hours after application

HAT = 290,000 AMB = 5,400 ng/m3

dC/dzPhe= 165,000 ng/m SPAH8 149 days after (during

winter) HAT=291 AMB = 28 ng/m3

dC/dzPhe = 180

35° C

34° 41°

31°

17°

11°

31°

Trends in Sum-PAH Concentrations

10

100

1,000

10,000

100,000

1,000,000

0 50 100 150 200 250 300 350 400

Days since sealing

SU

M P

AH

(n

g/m

3)

PIC-HAT

PIC-AMB

CT-HAT

CT-AMB

US-HAT

US-AMB

PAH Pickle test plot

R2 = 0.95 t1/2 = 7 days

Fluxes?Q = u* K’T [Ca(zhat) - Ca(zamb)] (1)

Q = flux [C – C] = air

concentration gradient u* K’T = mass transfer

coefficient

(1) Scholtz et al., 2002

u* K’T is primarily a function of wind speed

Flux = f (gradient)