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- Title
Site and Season Specific Calibrations Improve Low-cost Sensor Performance: Long-term Field Evaluation of PurpleAir Sensors in Urban and Rural India.
- Authors
Campmier, Mark Joseph; Gingrich, Jonathan; Singh, Saumya; Baig, Nisar; Gani, Shahzad; Upadhya, Adithi; Agrawal, Pratyush; Kushwaha, Meenakshi; Mishra, Harsh Raj; Pillarisetti, Ajay; Vakacherla, Sreekanth; Pathak, Ravi Kant; Apte, Joshua S.
- Abstract
We report on the long-term performance of a popular low-cost PM2.5 sensor, the PurpleAir PA-II, at multiple sites in India, with the aim of identifying robust calibration protocols. We established 3 distinct sites in India (North India: Delhi, Hamirpur; South India: Bangalore), where we collocated PA-II with reference beta-attenuation monitors to characterize sensor performance and to model calibration relationships between PA-IIs and reference monitors for hourly data. Our sites remained in operation across all major seasons of India. Without calibration, the PA-IIs had high precision (NRMSE among replicate sensors ≤ 15%) and tracked the overall seasonal and diurnal signals from the reference instruments well (Pearson's r ≥ 0.9) but were inaccurate (NRMSE ≥ 40%). We used a comprehensive feature selection process to create optimized site-specific calibrations. Relative to the uncalibrated data, parsimonious least-squares long-term calibration models improved PA-II performance at all sites (cross-validated NRMSE: 20-30%, R²: 0.82-0.95), particularly by reducing seasonal and diurnal biases. Because aerosol properties and meteorology vary regionally, the form of these long-term models differed by site. Likewise, using a moving-window calibration, we find a calibration scheme using seasonally specific information somewhat improves performance relative to a static long-term calibration model. In contrast, we demonstrate that a successful short-term calibration exercise for one season may not transfer reliably to other seasons. Overall, we demonstrate how the PA-II, when paired with a careful calibration scheme, can provide actionable information on PM2.5 in India with only modest irreducible uncertainty.
- Subjects
INDIA; ATMOSPHERIC aerosols; CALIBRATION; FEATURE selection; DETECTORS; SEASONS
- Publication
Atmospheric Measurement Techniques Discussions, 2023, p1
- ISSN
1867-8610
- Publication type
Article
- DOI
10.5194/amt-2023-35