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The rate of reaction of gas phase HO2 radicals with a monodisperse, submicrometer aerosol was measured in a flow tube reactor at atmospheric pressure. At the relative humidity of the experiments (75%), the aerosol consisted of concentrated solution droplets of either LiNO3 or NH4HSO4. When the aerosol contained a sufficient amount of Cu(II) ions, reaction of HO2 with the aerosol was observed. The mass accommodation coefficient for HO2 on aqueous particles was determined to be greater than 0.2. This implies that in clouds HO2 mass transport will be limited by gas-phase diffusion and HO2 will be in equilibrium at the gas-liquid interface. Reactions of HO2 with Cu(I) and Cu(II) ions in submicrometer aerosols may have a significant role in converting atmospheric odd hydrogen radicals into H202.

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In this paper an aerosol charger that largely avoids the production of multiply charged particles in the 0.1-1.0 pm diameter range is described. The input aerosol is first passed through an electrostatic condenser to remove all charged particles and ions. The remaining neutral aerosol then flows into a 23-cm-long, 2.1-cm inner diameter cylindrical tube; the inner surface of this tube is uniformly coated with 0.09 pCi 6 3~i , a 0.067 MeV p-emitter with a half-life of 92 years. At typical airflow rates of 0.2-1.0 Ipm, this low-activity source of ionizing radiation produces bipolar ion concentrations ranging from 1 X lo4 to 9 X lo4 ion/cn?, which is much lower than levels required to bring the aerosol to Bolkmann charge equilibrium. At a flow rate of 1.0 lpm, particles smaller than about 1.0 pm typically interact with no more than one ion en route through the charger. Therefore, particles at the charger exit are mostly either neutral or singly charged. Charge distributions of initially-neutral monodisperse polystyrene latex particles were measured at the exit from the charger for particle diameters ranging in size from 0.09 to 1.09 pm. It was found that, at an airflow rate of 1.0 Ipm and particle size 1.09 pm, the ratios of singly, doubly, and triply charged to total positively charged concentrations were 0.75, 0.19, and 0.06 respectively; particles with more than three charges were not detected. In contrast, the analogous charge ratio at Boltzmann equilibrium is 0.28 (+I), 0.24 (+2), 0.19 (+3), 0.13 (+4), 0.08 (+5), 0.05 (+6), and 0.02 (+7).

Higher accumulation of liposomal drug in inflammatory area and specific release of liposomes by enteric coated capsules provide better option for the treatment of colonic disease.

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