Scientific and Policy Motivations behind the Study of Houston Atmospheric Radical Precursors (SHARP) Field Experiment

The SHARP campaign was conceived by the Houston Advanced Research Center (HARC) on behalf of the Texas Environmental Research Consortium (TERC) as a result of initial modeling studies in support of the Texas State Implementation Plan (SIP) for the Houston-Galveston-Brazoria (HGB) ozone non-attainment area and subsequent observations during the TERC-funded portion of the Second Texas Air Quality Study (TexAQS II). The initial modeling studies indicated that the air quality simulation in the HGB SIP was possibly deficient in radical sources, and that peak ozone in the Houston region would respond significantly to as yet uncounted primary formaldehyde from industrial flares. This had major implications for the effectiveness of SIP control strategies as represented in ozone attainment demonstrations. Analysis of data from the TexAQS II Radical and Aerosol Measurement Project (TRAMP) and instrumented flights of the Baylor University Piper Aztec aircraft during the TexAQS II 2006 intensive showed intriguing evidence of primary formaldehyde from flares, as well as significant transient peaks in nitrous acid, another important radical precursor, possibly associated with traffic emissions and/or nocturnally formed secondary organic aerosol. SHARP was designed to further investigate both primary and secondary sources of formaldehyde and nitrous acid. For example, SHARP provided a unique opportunity to elucidate the multiphase chemistry involved in nitrous acid formation through a comprehensive suite of measurements at the top of the University of Houston's Moody Tower dormitory. Another interesting aspect of SHARP was the first ever deployment of a combination of novel remote sensing , in situ monitoring, and plume inverse modeling techniques to measure process-specific industrial emissions of a large suite of ozone and radical precursors from outside facility fence lines. Such hybrid monitoring approaches have the potential to enhance regulatory enforcement and to provide comprehensive industrial emission inventories beyond previous approaches.