Temporal and Spatial Variations of Black Carbon Concentration during DISCOVER-AQ Houston Texas 2013 Campaign

Abstract:

During the DISCOVER-AQ Houston Texas 2013 campaign, optical black carbon (BC) characterization of particulate matter (PM) were carried out through multiple parameters based on three different instruments: two at surface-based sites and one flight-based. A seven-wavelength portable Aethalometer deployed at Moody Tower on the University of Houston campus, an urban site, was under continuous measurement from August 29 to September 30, 2013. A Photoacoustic Extinctiometer (PAX) deployed at Manvel Croix, a suburban site 25 km away from Moody Tower, was running continuously from September 14 to September 30. Finally, a Single Particle Soot Photometer (SP2) was aboard the NASA’s P-3B aircraft for nine flight-days in September. Real-time BC concentrations from both of the ground sites have a sharp morning rush hour peak and a minor afternoon peak, indicating a pronounced contribution of morning rush hour traffic emission. The average hourly-averaged BC concentrations for the two surface-based instruments are correlated, for both their total measurement period (correlation coefficient R = 0.78) and their overlapped period (R = 0.7). The BC concentrations from the two surface-based instruments are less correlated with the BC concentration measured by SP2 (R = 0.4 for PAX with SP2 and R = 0.51 for Aethalometer with SP2) for their overlapped periods, due to the spatial variations. The morning rush hour peak for the urban site is earlier than the suburban location, suggesting a relatively more direct influence of high intensity traffic emission for the urban site and a transported influence of carbon particulate for the suburban site. Vertical gradient and spatial variation of the BC concentration based on SP2 measurement will be examined to understand source contributions and atmospheric transport of BC into the Houston area.