Wind-blown pollution at Horn Lane
This post is about the direction of PM10 pollution arrived at the Horn Lane sensor. Consider it an extension to Dee's thread on air pollution, which was getting rather unwieldy.The Horn Lane monitoring site reports wind speed and direction for the period February 2005 to February 2006, but not subsequently. Dr. John Freeman of Ealing Regulatory Services Division has kindly informed me that the wind sensor at that time was on a building within the Yeoman Aggregates site, while the PM10 sensor was at its current location in Horn Lane.The wind rose below was plotted from that data, and shows the likelihood of the wind coming from any particular direction, over the monitoring year. (Striations are likely caused by the original quantised wind angle not mapping evenly onto 360 compass points.) Clearly the prevailing wind comes from the west to south west. This plot says nothing about the source of pollution, but does say a lot about the responsiveness of the sensor. Pollution sources at any distance to the north-west (NW) or SE are unlikely to be spotted, as wind will seldom blow the pollution toward the sensor. Sources to the SW or NE, on the other hand, are very likely to be noticed.The Google map below displays the same wind rose, this time centred on the Horn Lane location of the PM10 sensor. Prevailing wind is roughly along the railway tracks, from left to right. The map is followed by a further graph, which plots wind-blown pollution.The next graph takes some explaining. Those who read Dee's thread may remember that PM10 pollution seemed to come from a regular emitter, which for convenience I will call a plant. The plant operated a full day on weekdays, and half day on Saturdays. PM10 samples from the year 2005 have been separated into two sets; one set from times of day when the plant was active, the other from times when the plant was inactive, such as Sundays. These sets were then plotted as two separate curves.The X axis shows wind direction. At any point on the axis, the data plotted is the average of samples that were collected when the wind happened to be from that direction. Data from SE and NW is particularly noisy because wind seldom blew from those directions.With the plant inactive, PM10 levels seem slightly less when the wind is from the west. A plausible explanation is that, as the sensor box is located on the west side of Horn Lane, a wind from the west would tend to blow away traffic pollution.When the plant is active, PM10 levels are highest when the wind is from the west to south west, suggesting strongly that the main pollution is coming from that direction.
Ian M Green ● 5909d25 Comments ● 5888d