Hourly elemental concentrations in ambient aerosols in four cities in Asia and Europe – comparison and source apportionment

Megacities worldwide are suffering from elevated air pollution due, e.g., to continuously increasing urbanization, and a sizeable amount of the population in such areas is exposed to particulate matter (PM) concentrations exceeding the WHO limits. Huge efforts are therefore undertaken to characterize the air pollution situation and to reduce or mitigate the impact on the population and the environment. Modern instrumentation allows for a quantitative determination of aerosol concentration and composition with high time resolution (minutes to hours), and subsequent source apportionment.We collected PM10 and PM2.5 aerosols alternatingly with an online X-ray fluorescence (XRF) spectrometer in the cities of New Delhi (India) in 2019, Beijing (China) in 2017, and Krakow (Poland) in 2018, with time resolutions from 30 to 120 min, and in London (UK) in 2012 with 3-stage rotating drum impactors and subsequent offline SR-XRF analysis. Campaigns lasted for two to seven weeks in fall and winter. Elements from Al to Bi were analyzed in near-real time, except for London.Our results show that some of the cities experience episodic extreme events, whereas extremely high elemental concentrations are chronic in others. Toxic metals are shown to be strongly location-dependent, and may occur in extreme plumes. Meteorological conditions also play an important role and will be discussed. The regional influence of fine PM, in comparison to the more local origin of coarse PM will be evaluated. The differences among the four cities, with substantially higher concentrations in the Asian cities than the European ones will be discussed. Highly time-resolved size-segregated sampling allowed for a rough classification of elements into five groups and will be described in detail. We demonstrate that the use of size information on toxic elements, diurnal patterns of targeted emissions, and local vs. regional effects are advantageous for formulating effective environmental policies to protect public health.