The characterisation of pollution aerosol in a changing photochemical environment

[摘要] Measurements are presented from a sampling location 50 km downwind ofGreater London, UK, to investigate the timescales required for theatmospheric transformations of aerosol in urban emissions plumes in thecontext of photochemical age based on the benzene to toluene ratio. It isshown that particles at or around 100 nm in diameter exhibit the greatestsystematic variability in chemical properties, and thus hygroscopicproperties, on a timescale of 1–2 days. The smaller Aitken mode and largeraccumulation mode particles exhibit less variability on these timescales,which we propose is as a result of their different residence times in theatmosphere. The larger accumulation particles have been in the atmospherelonger than the 100 nm particles and their chemistry and hygroscopicproperties have been integrated over several days and potentially overseveral source regions. In contrast, the smaller Aitken mode particles showlittle systematic variability with photochemical age because theiratmospheric lifetimes are short, thus chemical changes and hence changes inwater affinity have not had time to occur. Increases in the particlediameter of up to 40% are observed at 90% relative humidity in theaccumulation mode from the uptake of water as the particles becomeincreasingly soluble in nature.

[学科分类] 大气科学