Aerosol chemistry is often studied without considering microbial involvements. Here, we have applied a high-volume (1 m3/min) aerosol sampler and the Micro-Orifice Uniform Deposit Impactor (NanoMoudi) along with molecular and microscopic methods to investigate time-and size-resolved bacterial aerosol dynamics in air. Under high particulate matter (PM) polluted episodes, bacterial aerosols were detected to have a viability 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 pharmaceuticals and wastewater treatment, bacteria such as Psychrobacter spp., Massilia spp., Acinetobacter lwoffii, Exiguobacterium aurantiacum, and Bacillus megaterium were shown to have experienced massive abundance shifts in polluted air on early mornings and late afternoons, on which were previously reported to witness rapid new particle formation events. For example, Acinetobacter spp. were shown to account for > 96% abundance at a corresponding PM2.5 level of 208 μg/m3. The bacterial aerosol changes corresponded to the observed PM2.5 mass peak shift from 3.2-5.6 μm to the high viability size range of 0.56-1μm. Additionally, it is interesting that elevated levels of soluble Na, Ca, Mg, K, Al, Fe and P elements that are 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 and Massilia were shown to alternate in dominating the time-resolved aerosol community structures. The results from a HYSPLIT trajectory model simulation suggested that the role by air mass transport in affecting the observed bacterial aerosol dynamics could be minor. As an evidence, we found that Acinetobacter, Psychrobacter, Exiguobacterium, and Bacillus genera were emitted into the air with a level of > 3000 CFU/m3 from a pharmaceutical plant. In addition, high level of VOCs up to 15,030 ppbv, mainly Acetone (61%) and Acetaldehyde (11%), were also detected in the air inside the plant. All the data including size-resolved viability and time-resolved bacterial aerosol dynamics together with their growth conditions detected in the air suggested that airborne bacteria in the size range of 0.56- 1μm could have played important roles for haze formation in Beijing. The results about time- and size-resolved bacterial aerosol dynamics from this work provide a fresh understanding of aerosol chemistry especially in highly polluted air. It is hoped that these findings could lend a support in future cost-effective air pollution control practices.
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