To validate the efficacy and performance of the Pure Skies unit, continuous monitoring of PM10 and PM2.5 have been done at study locations. For the first week without the installation of control technology, baseline data was collected. During this time, air pollution data for PM10 and PM2.5 were collected every 5 minutes to assess pollution trends. Following the establishment of the baseline, the control system was installed in the location and turned on for a three-week period during which the data was collected and analyzed in the same way as the baseline period. After the intervention period, another week the control system kept off and collected the data to confirm the efficacy of the unit. The complete detail about the study is given in the supporting information the results were discussed in the results and discussion section. Additionally, to validate the technology, we have conducted lab studies in a controlled atmosphere (Chamber based analysis).
Experiments under a controlled atmosphere
Particulate matter is introduced into the chamber using a Powder feeder. The particle size and charge distributions are measured using APS (Aerodynamic Particle Sizer). Temperature and relative humidity inside the chamber were measured using humidity and temperature transmitter. The temperature inside the chamber was maintained by circulating the heated/cooled water through the reaction chamber.
Field Studies
The air quality is measured for a period of 14-days under the natural operational conditions to establish a baseline. The baseline air quality is compared to the air quality observed during the intervention period (after installing the unit in that location spanning for 2–3 weeks.
Study location. The study was conducted in three different indoor spaces: 1) An office space, 2) A departmental store, and 3) An indoor multiplex cinema hall.
The first study location was a private office space in an urban zone. This urban area is heavily populated and is one of the busiest places, and highly polluted with the outdoor 24-hour average PM2.5 and PM10 levels ranging between 80–100 µg/m3.
The second location was a department store. Due to an adjacent arterial road, the department store continuously faced poor indoor air quality.
The third location was an indoor multiplex cinema hall. Indoor air quality was poor due to its proximity to the mall parking lot, as well as generally poor outdoor air quality. In addition, most cinema halls lack fresh air as the indoor air is re-circulated through the air handling units.
Installation of the air pollution control unit. The pulsed radio wave units are housed in a fiber-reinforced plastic cabinet of size 2’(W) x 1’ (D) x 3’ (H). The complete unit comprises of a power source, a signal source, a circularly polarized transmitter antenna, quartz crystals for signal stability, the internet of things (IoT) - for communication from our laboratory to the unit, an uninterrupted power supply (UPS), and other hardware for electrical safety. The peak power consumption of each unit is 30 W.
One unit of the pollution control device was installed indoors at all three study locations. Additionally, an air quality monitor was installed at each location to measure air quality in real time. The air quality monitors were installed at a minimum distance of 30–50 m from the air pollution control unit.
Air quality monitoring. The levels of pollution in these locations were assessed continuously over the period of study using indoor air quality monitors. The air quality monitor for all our deployments is located at least 5–10 meters away from the pollution control equipment.
The air quality monitors such as TSI and PALAS were used for the field installation studies as well as experimental studies. Air quality data was measured using an indoor monitor to provide real-time data on air quality. The air quality parameters measured were PM10 and PM2.5 sensors, based on the principle of laser scattering. The sensors were pre-calibrated against reference-grade monitors prior to use.
Table 1
Monitoring Instruments Specifications
Specifications | TSI | PALAS |
---|
Make and model | DUST TRACK 8533 | Fidas Frog |
Principle used | Light Scattering | Aerosol spectrometer |
Range of measurement | 0–150000 µg/m3 | 0–50000 µg/m3 |
Sampling frequency | Continuous | Continuous |
Study protocol. To analyze the levels of particle pollutants, baseline air quality was measured at all the locations for a period of two weeks under normal operational conditions. After the baseline air quality was established, the pulsed radio wave technology was powered on and the air quality parameters were measured over a period ranging from one week up to one month, which marked the intervention period. Care was taken to ensure that both the baseline and intervention periods occurred during the same season. The air quality during the intervention period was compared to the baseline air quality. During the first month of the intervention period, a weekly comparison of the baseline and the intervention period was performed to understand the effective extent of reduction in pollutant levels. After the initial month of the technology period, a monthly analysis was performed to understand the overall reduction.
Data quality check and statistical analysis. The air quality data was assessed and analyzing the values and outliers. All values were presented as a mean ± standard deviation for continuous variables and as a percentage for categorical variables. The air quality data on the days when precipitation was recorded were excluded from the analysis. For evaluating the efficacy of the air pollution control units, at all the locations, the 24-hour average values of PM2.5 and PM10 were compared during the intervention vs. the baseline periods. For all analyses, p ≤ 0.05 was considered statistically significant. Statistical analysis of the data was performed using GraphPad Prism 8.3.1 (San Diego, USA). The statistical tests used for analysis included one-way ANOVA with relevant post-tests for multiple comparisons.