Microbial aerosol chemistry characteristics in highly polluted air

Aerosol chemistry is often studied without considering microbial involvements. Here, we investigated time-and size-resolved bacterial aerosol dynamics in air. Under high particulate matter(PM) polluted episodes, bacterial aerosols exhibited a viability of up to 50%–70% in the 0.56–1 μm size range, at which elevated levels of SO42-, NO3- and NH4+ were concurrently observed.Engineered or acclimated for both industrial use, bacteria such as Psychrobacter spp., Massilia spp., Acinetobacter lwoffii,Exiguobacteriumaurantiacum and Bacillusmegaterium were shown to have experienced massive abundance shifts in polluted air on early mornings and late afternoons, on which rapid new particle formation events were widely reported. Here, Psychrobacter spp. were shown to account for >96% abundance at a corresponding PM2.5 level of 208 μg/m3. These observed bacterial aerosol changes corresponded to the PM2.5 mass peak shift from 3.2–5.6 μm to the high viability size range of 0.56–1 μm. Additionally,elevated levels of soluble Na, Ca, Mg, K, Al, Fe and P elements, required for bacterial growth, were observed to co-occur with those significant bacterial aerosol structure shifts in the air. For particular time-resolved PM2.5 pollution episodes, Acinetobacter,Psychrobacter and Massilia were shown to alternate in dominating the time-resolved aerosol community structures. The results from a HYSPLIT trajectory model simulation suggested that air mass transport played a minor role in affecting the observed bacterial aerosol structure dynamics. All the data here suggested that airborne bacteria in the size range of 0.56–1 μm could be extensively involved in aerosol chemistry in highly polluted humid air.

In-situ generation and global property profiling of metal nanoclusters by ultraviolet laser dissociation-mass spectrometry

Metal nanoclusters are promising nanomaterials with unique properties, but only a few ones with specific numbers of metal atoms can be obtained and studied up to now. In this study, we establish a new paradigm of in-situ generation and global study of metal nanoclusters with different sizes, constitutions, and charge states, including both accurate constitution characterization and global activity profiling. The complex mixtures of metal nanoclusters are produced by employing single-pulsed 193-nm laser dissociation of monolayer-protected cluster(MPC) precursors within a high-resolution mass spectrometry(HRMS). More than400 types of bare gold nanoclusters including novel multiply charged(2+ and 3+), S-/P-doped, and silver alloy ones can be efficiently generated and accurately characterized. A distinct size(1 to 142 atoms)-and charge(1+ to 3+)-hierarchy reactivity is clearly observed for the first time. This global cluster study might greatly promote the developments and applications of novel metal nanoclusters.