Application of the variability-size relationship to atmospheric aerosol studies: estimating aerosol lifetimes and ages

[摘要] Aerosol variability is examined as function of particle size for data collectedover the Northern Indian Ocean in February 1999 as part of the INDOEX experiment.It was found that for particles believed to be of terrestrial or oceanic origin, thevariability correlated with the average number concentration. For particles that arethought to be formed and grow in the atmosphere through coagulation and condensation an anticorrelation was observed, the minimum in variability coincidingwith the maximum in the number concentration. Three altitude ranges were examined (0--1, 4--8 and8--13 km) and the minimum in variability was found to occur at lower particle sizes in the free troposphere(0.065 mm) than in the boundary layer(0.165mm). The observed variability has been compared to that generated by anumerical model in order to determine the relative importance of the physicalprocesses. Modelled variability of 0.02 mm particles caused by nucleation was notobserved in the measurements. A previously derived empirical relationship foraerosol residence time was compared with the measured variability as a function ofbin size. The aerosol variability / residence time relationship was characterised by acoefficient (b) at all altitudes and for both correlating and anticorrelating regimes. Bycombining the derived coefficient with the model predicted lifetime for0.020 mmparticles we estimated residence times and ages as a function of particle size andaltitude. General agreement was found with previous estimates of aerosol residencetime. In the upper atmosphere aerosols of 0.065 mmin size have residence times of approximately 1 month and can be transported on a hemispheric scale. The samesize aerosol has a lifetime one order of magnitude less in the boundary layer andtherefore will not be transported far from the source regions.

[学科分类] 大气科学