Since installing the SDS011 in its permanent location I have not had much opportunity to evaluate the data it has been collecting. My next significant goal in this regard is to collate the data from the weather station and the PM sensor (and of course my MQ135 sensor) all into one data stream to allow quick visual inspection to reveal obvious correlations.
I have been expecting to find, for instance, that wind direction will have a strong impact on the MQ135 air pollution readings. Our proximity to the South West Water Works means that we run the risk of foul air whenever the wind is out of the south. I have not known quite what to anticipate with the particulate matter readings. We are not far from a popular road route used to access a local two-form-entry primary school, so maybe I should expect peaks at drop off and pick up times? I do not think I have observed this.
What has become apparent is that when the wind is low the PM readings seem to go up. Especially if the (low speed) wind is out of the south. That's what has happened today. At approximately 1900 GMT, looking back over the past three hours I can see winds 0-2mph, direction ESE through SSE, with PM10 readings exceeding 100ug/m³ and PM2.5 hitting 85ug/m³. For those who prefer the AQI (Air Quality Index) scale that is:
PM10 102ug/m³ = AQI 74 Moderate
PM2.5 85ug/m³ = AQI 166 UNHEALTHY
The AQI warning associated with an "unhealthy" reading is as follows, "People with respiratory or heart disease, the elderly and children should avoid prolonged exertion; everyone else should limit prolonged exertion." You can find out more about the globally recognised Air Quality Index at airnow.gov.
My first thought was that this low speed southerly wind must be bringing pollution from the water works. But a quick look at Luftdaten revealed a far more widespread rapid increase in pollution at the same time across Eastbourne and indeed the UK, which rather rules out our local water works as the source of the problem.
Perhaps the dominant influence on this occasion is not the wind direction but the date. Remember, remember the fifth of November, gunpowder, treason and smog.
So more work remains to be done on evaluating the patterns of behaviour of airborne particulate matter pollution in Sovereign Harbour, Eastbourne. Watch this space for further observations!