Effect of humidity on nitric acid uptake to mineral dust aerosol particles

[摘要] This study presents the first laboratory observation of HNO₃ uptake byairborne mineral dust particles. The model aerosols were generated by drydispersion of Arizona Test Dust (ATD), SiO₂, and by nebulizing asaturated solution of calcium carbonate. The uptake of ¹³N-labeledgaseous nitric acid was observed in a flow reactor on the 0.2–2 s reactiontime scale at room temperature and atmospheric pressure. The amount ofnitric acid appearing in the aerosol phase at the end of the flow tube was found to be a linear function of the aerosol surfacearea. SiO₂ particles did not show any significant uptake, while theCaCO₃ aerosol was found to be more reactive than ATD. Due to thesmaller uncertainty associated with the reactive surface area in the case ofsuspended particles as compared to bulk powder samples, we believe that weprovide an improved estimate of the rate of uptake of HNO₃ to mineraldust. The fact that the rate of uptake was smaller at a concentration of 10¹²than at 10¹¹ was indicative of a complex uptake mechanism. The uptake coefficient averaged over the first 2 s of reaction time ata concentration of 10¹² molecules cm^-3 was found to increase withincreasing relative humidity, from 0.022±0.007 at 12% RH to0.113±0.017 at 73% RH , which was attributed to an increasing degree of solvation of the more basic minerals.The extended processing of the dust by higher concentrations of HNO₃ at 85% RH led to a water soluble coating onthe particles and enhanced their hygroscopicity.

[学科分类] 大气科学