Improved method for characterising temporal variability in urban air quality part II: Particulate matter and precursors in central Poland

Four years (2008-2011) of air quality observations are investigated near Lodz, central Poland. Despite reduced industrialisation in the region since around 1990, peak hourly PM10 (PM2.5) occasionally exceeded 400 (300) mu g m(-3) in the 'heating season' (Oct-Mar), attributable to a combination of 'imported' pollution and local traffic-related and domestic sources. High heating season emissions caused annual-mean PM10 and PM2.5 values of 33.6 and 21.1 mu g m(-3) (13.6 and 11.1 mu g m(-3), respectively, above the WHO guidelines), with daily mean PM10 exceeding the WHO guideline of 50 mu g m(-3) 56 times a year. An approach is outlined by which urban air quality can be more directly related to local meteorology by separate consideration of atmospheric stability on diurnal, synoptic and seasonal timescales. Newly developed radon-based techniques for classification of diurnal and synoptic timescale changes in stability are adapted for use in this study. Daily PM10 and PM2.5 exceeded WHO guidelines for only two of six mixing state categories: (i) strong persistent synoptic inversion conditions, associated with lingering and-cyclonic systems in the non-summer months (comprising <= 15% of heating season months), and (ii) fine-weather conditions conducive to the formation of strongly stable nocturnal boundary layers (15-20% of heating season months). Both mixing states were associated with low mean wind speeds (1-1.5 m s(-1)), near-surface temperature gradients of 1-2 degrees C m(-1), shallow nocturnal boundary layers (45-55 m), and south-easterly winds. Radon-based stability "class-typing" is shown to constitute a convenient, consistent, objective and economical means by which to relate local meteorological conditions to air quality in complex urban environments. It also provides a statistically-robust method of retrospectively relating exposure to poor air quality to likely health implications.