Performance evaluation of Atmotube PRO sensors for air quality measurements in an urban location

<p>This study presents a performance evaluation of eight Atmotube PRO sensors using US Environmental Protection Agency (US EPA) guidelines. The Atmotube PRO sensors were collocated side by side with a reference-grade Fidas monitor in an outdoor setting for a 14-week period in the city centre of Leeds, UK. We assessed the linearity and bias for PM<span class="inline-formula">₁</span>, PM<span class="inline-formula">_2.5</span>, and PM<span class="inline-formula">₁₀</span>. The result of the PM<span class="inline-formula">_2.5</span> assessment showed the Atmotube PRO sensors had particularly good precision with a coefficient of variation (CoV) of 28 %, 18 %, and 15 % for PM<span class="inline-formula">_2.5</span> data averaged every minute, hour, and day, respectively. The inter-sensor variability assessment showed two sensors with low bias and one sensor with a higher bias in comparison with the sensor average. Simple univariate analysis was sufficient to obtain good fitting quality to a Fidas reference-grade monitor (<span class="inline-formula"><i>R</i>²&gt;0.7</span>) at hourly averages, although poorer performance was observed using a higher time resolution of 15 min averaged PM<span class="inline-formula">_2.5</span> data (<span class="inline-formula"><i>R</i>²</span> of 0.48–0.53). The average error bias, root mean square error (RMSE), and normalized root mean square error (NRMSE) were 3.38 <span class="inline-formula">µ</span>g m<span class="inline-formula">⁻³</span> and 0.03 %, respectively. While there were negligible influences of temperature on Atmotube PRO-measured PM<span class="inline-formula">_2.5</span> values, substantial positive biases (compared to a reference instrument) occurred at relative humidity (RH) values <span class="inline-formula">&gt;</span> 80 %. The Atmotube PRO sensors correlated well with the PurpleAir sensor (<span class="inline-formula"><i>R</i>²</span> of 0.88, RMSE of 2.9 <span class="inline-formula">µ</span>g m<span class="inline-formula">⁻³</span>). In general, the Atmotube PRO sensors performed well and passed the base-testing metrics as stipulated by recommended guidelines for low-cost PM<span class="inline-formula">_2.5</span> sensors. Calibration using the multiple linear regression model was enough to improve the performance of the PM<span class="inline-formula">_2.5</span> data of the Atmotube PRO sensors.</p>