As part of the 2009 SHARP (Study of Houston Atmospheric Radical Precursors ) project, aircraft-based and ground-based measurements of SO₂, CH₂O, CO, NO_x NO_y and alkenes were made of the Houston-Galveston urban area, the Houston Ship Channel (HSC), and the Mt Belvieu area. Sources of ambient mixing ratios of formaldehyde include biogenic, mobile or industrial sources through either primary or secondary formation. This work investigates these sources by utilizing CH₂O/CO, CH₂O/NO_y, SO₂/CH₂O ratios and other methods to categorize these sources.