Bi-annual frequencies, seasonal frequencies, and meteorological summaries for each SOM multipollutant day type. Panels (a-d) map bi-annual frequency counts for each multipollutant day type to the SOM grid. Panels (e-h) map seasonal frequencies of day types to the SOM grid. Panels (i-l) map the average (standard deviations) local weather conditions observed under each day type to the SOM grid. (Lighter grey tones indicate lower values and darker shades indicate higher values).