Update on the Optimization of U.S. EPA Method TO-11A for the Measurement of Carbonyls in Ambient Air

Best Practices in Indoor and Outdoor Air Monitoring
Oral Presentation

Prepared by

Contact Information: [email protected]; 614-424-3242


Update on the Optimization of U.S. EPA Method TO-11A for the Measurement of Carbonyls in Ambient Air

Ian C. MacGregor1,*, Elizabeth A. Hanft1, and David M. Shelow2

1Battelle, 505 King Ave. Columbus, OH 43201
2US EPA OAQPS, 109 TW Alexander Dr., Durham, NC 27711
*Corresponding author: [email protected], 614-424-3242

Monitoring agencies across the U.S. employ US EPA Compendium Method TO-11A for the determination of trace levels of carbonyl compounds such as formaldehyde and acetaldehyde in ambient air. Yet there are known shortcomings, some published in the peer-reviewed literature, with Method TO-11A. These include interferences with co-collected moisture and oxidants as well as inefficiencies in compound collection, all of which may adversely affect the methodís accuracy, sensitivity, selectivity and robustness. The objective of this work is to investigate the various limitations of the current monitoring method and to subsequently devise and implement workarounds and procedural improvements, as needed, to optimize the methodís functionality. To this end, laboratory testing has been and continues to be conducted to evaluate the effects of flow rate and co-collected humidity, ozone (O3), and nitrogen dioxide (NO2) on what has become the standard carbonyl sampling and analysis approach. We are evaluating the methodís performance for four target carbonyls of primary interest to the air toxics community, including formaldehyde, acetaldehyde, propionaldehyde, and benzaldehyde. To date we have assessed, at four different humidities (10, 30, 65, and 85%) and on the two commercial DNPH cartridge types (Waters and Supelco): (a) collection efficiencies of the four target carbonyls at various flow rates; (b) the capacity and efficiency of two types of KI ozone denuders at a flow rate of 1 L/min; (c) and the impact of ambient levels of NO2 on the measurement of formaldehyde. Preliminary data show that collection efficiencies for the four target carbonyls are nearly 100% across a flow rate range of 0.25 to 1.25 L/min over a 24 hour sampling duration when carbonyl concentrations are approximately 5 ppb and the relative humidity (RH) is either 30% or 65% at a typical collection temperature of 20 to 25įC. In addition, the two ozone denuders quantitatively and continuously remove O3 at 150 ppb in a 1 L/min stream at all four humidities over 30 days, consistent with the capacity required to remove ~70 ppb of O3 over a year of 1:6 sampling. Inaccuracy in the measurement of formaldehyde due to interferences from co-collected NO2 appears to be avoidable under appropriate chromatographic separation conditions. We expect experimental work to be complete by the time of our presentation and will provide more results at that time. The final outcome of this work will be a set of recommendations for how to best implement TO-11A for measurement of carbonyls at trace levels in ambient air.