title: Enhanced air pollution via aerosol-boundary layer feedback in China.
abstract: Severe air pollution episodes have been frequent in China during the recent years. While high emissions are the primary reason for increasing pollutant concentrations, the ultimate cause for the most severe pollution episodes has remained unclear. Here we show that a high concentration of particulate matter (PM) will enhance the stability of an urban boundary layer, which in turn decreases the boundary layer height and consequently cause further increases in PM concentrations. We estimate the strength of this positive feedback mechanism by combining a new theoretical framework with ambient observations. We show that the feedback remains moderate at fine PM concentrations lower than about 200 μg m(-3), but that it becomes increasingly effective at higher PM loadings resulting from the combined effect of high surface PM emissions and massive secondary PM production within the boundary layer. Our analysis explains why air pollution episodes are particularly serious and severe in megacities and during the days when synoptic weather conditions stay constant.
authors.affiliation: Department of Physics, University of Helsinki, Finland.|Joint International Research Laboratory of Atmospheric and Earth System Sciences &School of Atmospheric Sciences, Nanjing University, China.
authors.forename: T
authors.initials: T
authors.lastname: Petäjä
authors.affiliation: Department of Physics, University of Helsinki, Finland.
authors.forename: L
authors.initials: L
authors.lastname: Järvi
authors.affiliation: Department of Physics, University of Helsinki, Finland.
authors.forename: V-M
authors.initials: VM
authors.lastname: Kerminen
authors.affiliation: Joint International Research Laboratory of Atmospheric and Earth System Sciences &School of Atmospheric Sciences, Nanjing University, China.
authors.forename: A J
authors.initials: AJ
authors.lastname: Ding
authors.affiliation: Joint International Research Laboratory of Atmospheric and Earth System Sciences &School of Atmospheric Sciences, Nanjing University, China.
authors.forename: J N
authors.initials: JN
authors.lastname: Sun
authors.affiliation: Department of Physics, University of Helsinki, Finland.|Joint International Research Laboratory of Atmospheric and Earth System Sciences &School of Atmospheric Sciences, Nanjing University, China.
authors.forename: W
authors.initials: W
authors.lastname: Nie
authors.affiliation: Department of Physics, University of Helsinki, Finland.
authors.forename: J
authors.initials: J
authors.lastname: Kujansuu
authors.affiliation: Joint International Research Laboratory of Atmospheric and Earth System Sciences &School of Atmospheric Sciences, Nanjing University, China.|Finnish Meteorological Institute, Helsinki, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Virkkula
authors.affiliation: Joint International Research Laboratory of Atmospheric and Earth System Sciences &School of Atmospheric Sciences, Nanjing University, China.
authors.forename: X-Q
authors.initials: XQ
authors.lastname: Yang
authors.affiliation: Joint International Research Laboratory of Atmospheric and Earth System Sciences &School of Atmospheric Sciences, Nanjing University, China.
authors.forename: C B
authors.initials: CB
authors.lastname: Fu
authors.affiliation: Department of Physics, University of Helsinki, Finland.|Finnish Meteorological Institute, Helsinki, Finland.|University of Nizhny Novgorod, Nizhny Novgorod, Russia.|Moscow State University, Moscow, Russia.|Institute of Geography, Russian Academy of Sciences, Moscow, Russia.
authors.forename: S
authors.initials: S
authors.lastname: Zilitinkevich
authors.affiliation: Department of Physics, University of Helsinki, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Kulmala
mesh_terms: D000336:Aerosols / Q000032:analysis*; D000397:Air Pollution / Q000032:analysis*; D002681:China; D005246:Feedback; D052638:Particulate Matter / Q000032:analysis; D053260:Soot / Q000032:analysis; D013472:Sunlight; D013997:Time Factors
chemical_list: D000336:Aerosols; D052638:Particulate Matter; D053260:Soot