EFFECT OF NITROUS-ACID ON LUNG-FUNCTION IN ASTHMATICS - A CHAMBER STUDY

Nitrous acid, a component of photochemical smog and a common indoor ai r pollutant, may reach levels of 100 ppb where gas stoves and unvented portable kerosene heaters are used. Nitrous acid is a primary product of combustion and may also be a secondary product by reaction of nitr ogen dioxide with water. Because the usual assays for nitrogen dioxide measure several oxides of nitrogen (including nitrous acid) together, previous studies of indoor nitrogen dioxide may have included exposur e to an health effects of nitrous acid. To assess the respiratory effe cts of nitrous acid exposure alone, we carried out a double-blinded cr ossover chamber exposure study with 11 mildly asthmatic adult subjects . Each underwent 3-hr exposures to 650 ppb nitrous acid and to filtere d room air with three 20-min periods of moderate cycle exercise. Sympt oms, respiratory parameters during exercise, and spirometry after exer cise were measured. A statistically significant,decrease in forced vit al capacity was seen on days when subjects were exposed to nitrous aci d. This effect was most marked at 25 min and 85 min after exposure beg an. Aggregate respiratory and mucous membrane symptoms were also signi ficantly higher with nitrous acid. We conclude that this concentration and duration of exposure to nitrous acid alters lung mechanics slight ly, does not induce significant airflow obstruction, and produces mild irritant symptoms in asthmatics.