In vitro methemoglobin formation in human blood exposed to NO2.

The in vitro formation of methemoglobin in human blood was determined for various NO2 concentrations and exposure times. Blood was exposed either to measured amounts of NO2 in air or to a continuous flow of known concentrations of NO2 in air. CO2 was added to the gas phase to maintain pH and PCO2 in a normal range. Exposure to 45 ppm NO2 oxidized 95% of the total hemoglobin (THb) in 5 hr. Six ppm NO2 oxidized 17% of THb in 3 hr. Differences between in vitro and in vivo NO2 results are discussed.