Essay The Performance Evaluation of the Low-Cost OPCs – Essay Writing Assignment Help

Assignment Task:

Results and Discussion

The following sections present the performance evaluation of the low-cost OPCs prior to the correction, and the subsequent results post their machine learning field calibration. Firstly, the performance of the low-cost OPCs is compared against the reference instruments. The assessment for the same is discussed as per the criteria mentioned in the CFR Parts 58- Ambient Air Quality Surveillance (Subchapter C) of EPA. Thereafter, the results of (1.) and (2.) of the field calibration method are discussed. Finally, the cumulative results of the proposed calibration method are compared with the reference concentrations in the test dataset to determine if the low-cost OPCs meet the EPA’s criteria after the field calibration.

Performance Evaluation of OPC-N2

Fig.2 portrays the comparison of low-cost OPCs’ firmware and calculated PV2.5 and PV10 relative to the reference concentrations for the entire data collection campaign. In this duration, when the ReNEWW house was occupied, the OPCs’ raw calculated PV2.5 mean for a 30-minute time-averaging window was 0.52 µg/m3 (OPC 1) and 0.54 µg/m3 (OPC 2). For the same duration and time-averaging window, the mean PV2.5 measured by the reference instrument was 2.65 µg/m3. This suggests a major underestimation of PV2.5 calculated from both the OPCs. Similar findings were observed for OPCs’ calculated PV10 as well (Mean concentrations – OPC 1: 2.84 µg/m3, OPC 2: 2.76 µg/m3 and Reference: 7.45 µg/m3; 30-minute time-averaging window). However, the firmware outputs of the OPCs showed a little improvement in measurements compared to the raw calculated concentrations (Mean PV2.5 – OPC 1: 1.91 µg/m3, OPC 2: 2.02 µg/m3; Mean PV10 – OPC 1: 3.87 µg/m3, OPC 2: 4.37 µg/m3; 30-minute time-averaging window). This is because the selected OPC performs a proprietary self-calibration for its firmware outputs [17]. Nevertheless, despite the improvements, the firmware outputs also underestimated the particle concentrations compared to the reference values.

To quantify the difference in OPCs’ and reference instrument’s PV measurements, the accuracy metrics discussed in the previous section were estimated. Each of the accuracy metric is calculated for PV concentrations averaged over 30-minute window, and for the period when ReNEWW house was occupied. The MAPE for comparison of OPCs’ calculated PV2.5 relative to the reference PV2.5 was observed to be 79.81 % (OPC 1) and 78.97 % (OPC2). For calculated PV10, the MAPE was found to be 67.67 % (OPC 1) and 67.59 % (OPC 2).

The ReNEWW house remained unoccupied between 15th December 2018 and 5th January 2019. For this duration, substantial lower PV concentrations were recorded by both the OPCs (Mean PV2.5 – OPC 1: 0.15 µg/m3 (Calculated) and 0.53 µg/m3 (Firmware), OPC 2: 0.14 µg/m3 and 0.49 µg/m3 (Firmware); Mean PV10 – OPC 1: 0.36 µg/m3 and 1.57 µg/m3 (Firmware), OPC 2: 0.34 µg/m3 and 1.67 µg/m3 (Firmware); 30-minute time-averaging window). The reference instruments, being costly in nature, were not operated during this period. 

While measurements provided by OPCs (calculated and firmware) differed substantially from the reference concentrations, the OPCs were observed to behave similarly with each other throughout the measurement campaign (Fig.2). To confirm this hypothesis, the mean CV between PV concentrations (averaged over 30-minute window) measured by both OPCs (calculated and firmware) was calculated for the entire data collection campaign. The mean CV values for calculated and firmware PV2.5 were 4.82 % and 4.07 %, respectively. For PV10, CV values observed were 4.94 % and 8.73 % for calculated and firmware concentrations, respectively. These reported CV values were within the limits recommended by EPA (in the CFR Parts 58- Ambient Air Quality Surveillance (Subchapter C)). This indicates that both the OPCs were consistent with respect to each other in terms of output concentrations. In a laboratory analysis, Sousan et al. [17] reported a similar range of mean CV values for the selected OPC’s PM concentrations (4.2% to 9.5%).