| The lower part of atmosphere is most closely related to human activities.The chemical composition of atmospheric particulate matter is of great importance to its climatic and environmental effects.There are limit number of studies on the vertical observation for the chemical composition of atmospheric particles in the lower atmosphere.This is mainly impeded by the limitation of sampling platform,sampler and the amount of materials required for chemical analysis.In this study,two particle sampling systems were constructed to overcome these limitations when combining UAV(Unmanned Aerial Vehicles)sampling and single particle analysis for chemical composition.The multi-channel particle sampling system is based on the commercial impaction sampler,which allows collecting particles in different size ranges with remote control.The multi-sample position particle sampling system can collect up to 20 particle samples with high temporal and spatial resolution through remote control.The total weight of the system is only 2.2 kg with the cutting size(d50)of 0.5 μm at the sampling flow of 4.2 L/min.In 2019,two sampling systems were tested during the field observations in Xiamen and Shenzhen.Different types of scenarios or applications were designed and implemented including high-resolution vertical flights,high-resolution horizontal flights,diurnal vertical flights and dual UAVs joint flights.To obtain statistically significant information for particle chemical composition,about 1000-2000 particles for each sample were analyzed by scanning electron microscopy/X-ray spectrometer.Results show that the two sampling systems carried by UAVs for particle sampling in the lower atmosphere and the number of particles are suitable for single-particle analysis.In this study,UAV particle sampling and single particle analysis techniques are successfully applied to obtain the morphology and elemental information at Xiamen and Shenzhen sites.The vertical observation based on the multi-channel particle sampling system shows that,during the observation period,the supermicron particles(>1μm)are mainly sea salt particles,whereas the submicron particles(<1 μm)are mainly sulfur-containing particles.Using the multi-sample position particle sampling system,a vertical resolution of 30 meters has been achieved with a height of 500 meters.The horizontal observation at the sea-land interface indicates that particle composition is affected by both land and marine sources.During the observation,there is clear diurnal variation in contribution of sulfur-containing particles and sea salt particles to particle population for the selected case.During the simultaneous observations using dual UAVs,there is no significant difference in particle composition between the Yangmeikeng site and the met tower site in Shenzhen,however sea salt particles show different degrees of chloride depletion.In this study,we verify that the two particle sampling systems based on UAV can be used for atmospheric vertical observation,and can be further applied to study the transport and aging processes,local emission,biomass burning events and sandstorm events. |
