Experimental Study On The Effect Of Ammonia On The Secondary Organic Aerosol Formation

The secondary organic aerosol?SOA?had a significant contribution to the formation of PM_2.5 pollution events.Volatile organic compounds?VOCs?and ammonia?NH₃?were important precursors of secondary organic aerosol.NH₃ from non-agriculture source had a close link with the atmospheric pollution in urban areas due to the deficiency of relevant controlling strategies.In this study,an oxidation flow reactor?OFR?system was custom-built.The influence mechanism of NH₃ to secondary organic aerosol under different complex scenarios was investigated,based mainly on OFR experiments and also on some smog chamber experiments.The detail work of this study was listed as below:?1?An OFR system was custom-built,and the airtightness of chamber,flowing characteristics,OH exposure and reproducibility of experiments were characterised.A maximum equivalent atmospheric aging time of?5.2 days could be simulated by the OFR under different light intensity with the total gas flow rate of 4 L/min.?2?The effects of NH₃ on SOA formation were studied in the isoprene/O₃ and isoprene/OH reaction systems with the OFR.The results showed that the growing potential of particle size was higher and the number concentration of nuclei particles was lower in the presence of NH₃ in the isoprene/O₃ reaction system,resulting in the decrease of particle mass concentration and less oxidation for reaction products.The presence of NH₃ in the isoprene/OH reaction system could also increase the growing potential of particle size and the number concentration of nuclei particles,resulting in the increase of particle mass concentration and less oxidation for reaction products.?3?The effects of NH₃ on SOA formation under different complex polluted scenarios were studied in the toluene/OH reaction system with the OFR.The results showed that the growing potential of particle size was higher and the number concentration of nuclei particles was lower in the presence of NH₃,resulting in the decrease of particle mass concentration and less oxidation for reaction products.However,the presence of NO or SO₂ could increase the growing potential of particle size and the number concentration of nuclei particles,resulting in the increase of SIA and SOA mass concentration and less oxidation for reaction products.It was probable that the SIA which formed during the experiment supplied a surface for the deposition of organic vapours and promoted the formation of SOA.?4?The effects of NH₃ and relative humidity?RH?on toluene SOA were investigated in the toluene/NOx photo-oxidation with a smog chamber.The results showed that the particle size of SOA decreased while the particle number concentration increased in the presence of NH₃ or high RH.The onset of particle formation was earlier with increased RH.The major compositions of SOA were carboxylic acid,ketone and aldehyde,which had strong extinction effects.The extinction effect might change under the influence of NH₃ or high humidity conditions.