title: windRose in openair package: how to control PM10 concentration?
body: <p>In <code>openair</code> package, <code>windRose</code> function linked wind direction between PM10 concentration. For example:</p>
  
  <pre><code>windRose(mydata, type = "pm10", layout = c(4, 1))
  </code></pre>
  
  <p>Wind rose for four different levels of PM10 concentration. The levels are defined as the four quantiles of PM10 concentration and the ranges are shown on each of the plot labels.
  <img src="https://i.stack.imgur.com/ohjGC.png" alt="">
  Does anyone know how to control the PM10 concentration in those four figures ? For example, I want to make plots showing the PM10 concentration in "1 to 40", "40 to 75", "75 to 100" and "100 to 801"</p>