A CONTINUOUS MONITORING-SYSTEM FOR STRONG ACIDITY IN AEROSOLS

Inhalation of acid aerosols is believed to be a major source of respir atory ailments. A fully automated instrument that can measure acidity levels meaningful to real situations is described. A 5-10 L/min sampli ng rate is used. First, coarse particles are removed by a cyclone, fol lowed by the removal of acid and basic gases with a parallel plate wet denuder, Aerosols are then collected with a vapor condensation aeroso l collection system (VCACS). The VCACS provides an aqueous liquid effl uent in which all soluble constituents are present in the dissolved fo rm and the undissolved material remains suspended. The effluent is con centrated sequentially on a cation exchanger and an anion exchanger, w hich respectively constitute the injection loops of cation and anion a nalysis subsystems. In the first system, non-H+-cations (primarily NH4 +) are conductometrically determined as the corresponding hydroxide by elution with a strong acid plug and conductivity suppression with a h ydroxide-form anion exchanger. In the second system, total (strong aci d) anions are conductometrically determined by elution with a carbonat e/hydroxide-based eluent and continuous suppression by a Nation-based cation exchanger fiber suppressor; Aerosol strong acidity is determine d on the basis of charge balance: H+ equivalents present = Sigma anion equivalents - Sigma non-H+ cation equivalents. The system is operated continuously, typically sampling for 5-8 min at 5 L/min with an 8-10- min cycle providing a limit of detection (LOD) of 7-38 mmol m(-3) in t hat sampling cycle. For a greater sample volume, e.g., 300 L, the LOD is 0.6-3.2 mmol m(3), depending on the amount of total neutral salts c oncurrently present. No significant interference from acidic or basic gases has been found. The instrument was successfully used to measure acidity arising from kerosene-fueled indoor space heaters and the degr ee of neutralization of acidity in deliberate human exposure experimen ts by expired ammonia.