N-nitrosodimethylamine (NDMA): a potent carcinogen in clouds and fogs

James Hutchings (1), PIERRE HERCKES (1), Barbara Ervens (2,3)

(1) Arizona State University, Tempe, AZ, (2) CIRES, University of Colorado, Boulder, CO, (3) NOAA, ESRL/CSD, Boulder, CO

     Abstract Number: 157
     Last modified: November 6, 2009

Abstract
Air pollution events including photochemical smog and high particulate matter episodes have been associated with adverse health effects. Many carcinogenic and mutagenic species have been detected in the atmospheric gas or particle phase. In recent work, carcinogenic nitrosamines have been detected in cloud and fog water. In particular, N-nitrosodimethylamine (NDMA) is a potent carcinogenic species that is very water soluble. NDMA is currently under scrutiny for its occurrence as a disinfection byproduct in drinking water. NDMA has been shown to occur in the atmosphere; however these measurements were mostly in industrial and manufacturing areas. Overall, very few measurements of NDMA in the atmosphere have been conducted as it is believed that NDMA photolyzes quickly during the day time.

The occurrence of NDMA has been investigated in radiation fog and cloud samples. NDMA concentrations ranging from 243ng/L (Fresno, CA) to 362ng/L (Selinsgrove, PA) to 208ng/L in clouds in northern Arizona have been observed. The source of NDMA in atmospheric droplets has been investigated through field and laboratory studies. Laboratory studies on aqueous phase cloud chemistry suggest that homogeneous aqueous phase formation, while possible, is not able to explain the high concentrations found in atmospheric droplets. Substantial (greater than 1ppm) concentrations of the precursor species dimethylamine and nitrite would be required to achieve the observed concentrations of NDMA. The observations made suggest that the source of aqueous NDMA would be gas phase NDMA that forms either through gas phase or heterogeneous reactions followed by partitioning into the aqueous phase.

To explore the possible formation and loss pathways for NDMA in the atmosphere, a chemical box model was used. This model includes aqueous and gaseous formation pathways including the exchange between the phases. The results suggest that gas phase formation of NDMA followed by partitioning is the predominant pathway to the aqueous NDMA.