Description of the Calendar Plot tool

The Openair Calendar Plot tool provides a way of visualising trends in daily pollutant concentrations across a year in the familiar form of a calendar. Concentrations are represented with a colour scale and the meteorological conditions can be represented using arrows giving the vector averaged wind direction, scaled according to the wind speed based on modelled wind speed and direction from data from the UK air quality forecast. In this way pollution episodes can be identified by date and sources potentially indicated by the combination of pollutant and meteorological conditions.

The pollutants measured at each site are shown in the variables box once a site has been selected from the drop-down list of site names at the top of the page. Calendar plots can only be produced for one site and one pollutant at a time on this website.

Data can be plotted by year according to the availability of pollutant data and if choosing to annotate by wind direction and speed, the availability of modelled wind speed and direction data from the UK air quality forecast. The options to annotate have been restricted to 'Date' or 'Wind speed and direction' on this website.

The Colours drop-down menu allows the user more control over the colour scheme used to plot which can be useful to highlight pollution episodes and a variety of colour palettes are available. The colour presented for a particular day on the calendar represents the daily mean (Openair default) on this website. There are further options available through using the full Openair package, in particular to control both the annotation of the plot and in setting colour schemes that differentiate values above and below a threshold. Openair allows a data capture threshold to be set where averaging is applied using this tool. A data capture threshold of 75% has been set for the Calendar Plot function, meaning that 75% of data has to be present for the average to be calculated.