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Unconventional oil and natural gas (UONG) exploration and production have grown rapidly and are expected to increase further in the United States and internationally. Direct measurements of key air pollutant emissions from UONG are limited, especially during drilling and completion (hydraulic fracturing and flowback) of new wells. Knowledge of emission rates (ERs) of air toxics and other air pollutants from these activities is urgently needed to inform public policy. To address this key knowledge gap, we use a tracer ratio method to quantify pad-level, activity-specific [drilling, hydraulic fracturing (“fracking”), flowback, and production] ERs of 46 VOCs in the Denver-Julesburg (D-J, a mixed oil and gas play) and Piceance (primarily natural gas) basins in Colorado. Large differences in ERs of individual VOCs were observed across operation types, across facilities conducting the same operation type, and over time during a single operation. ERs of benzene and most VOCs were highest in both basins during flowback, when injected fracking fluids and produced water flow to the surface. ERs from production are much lower, an important result given the significant difference in the duration of activity (days to weeks for flowback vs decades for production). Fracking ERs of light alkanes and benzene were higher in the Piceance Basin than in the D-J Basin. Findings from this study provide important new information that can be used to evaluate potential health hazards and other air quality impacts of unconventional oil and gas activities in Colorado’s two major oil and gas production basins.

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Core Ideas Evapotranspiration from ASCEDM, ASCEDC was equivalent to lysimeters. Net radiation from global irradiance is sufficient in daily‐step model in absence of measured net radiation. ASCEDC improves irrigation scheduling in turfgrass when measured net radiation is not available. Evapotranspiration (ET) from turfgrass can be measured directly using lysimeters (LYS), estimated from weather data using models, or approximated using atmometers. Evapotranspiration measurements from LYS were compared with ET estimates from the American Society of Civel Engineers standardized ET equation using hourly steps from measured net radiation (Rn) (ASCEHM) and Rn calculated from global irradiance (ASCEHC), and daily steps from measured net radiation (ASCEDM) and Rn calculated from global irradiance (ASCEDC), the Priestley–Taylor (PT) model, and atmometers, all collocated in a sward of tall fescue (Festuca arundinacea Schreb.) turfgrass near Manhattan, KS. Data were collected on precipitation free days during the growing seasons 2010 through 2012 and analyzed by periods with high ET, low ET, and pooled across all days. Overall mean ET (May–October) ranged from 5.58 (LYS) to 4.47 mm d−1 (ASCEHC). During days with high evaporative demand ET from daily‐step models (ASCEDM, ASCEDC) were equivalent to LYS, based on paired t tests. Similarity in ET among LYS, ASCEDM, and ASCEDC indicate using Rn calculated from global irradiance is sufficient in the daily‐step model in the absence of measured Rn. At high ET rates ET from ASCEHM and PT was 5 to 9% lower than LYS, but accuracy was significantly reduced (by 22%) with ASCEHC. Atmometer ET averaged 17% lower than LYS, but performance was better at low than high ET. Results indicate the ASCEDC could improve irrigation scheduling in turfgrass by providing accurate ET estimates from standard weather station data where measured Rn is not available.