Accuracy of estimating a human-sighted visual range for short-term particulate matter concentration in Chiang Mai, Thailand

Background: Haze crisis in the North Thailand has occurred more than decade. Although four air monitoring stations (Air4Thai) are installed in Chiang Mai, three stations are in the city. According to the California Department of Public Health, communities have used both measurement devices and visual estimates as the concentration of smog changes quickly. Therefore, particle levels are estimated from visual assessments or visual views as another measurement as well. This study aims to assess whether human-sighted visual range is reliable or not in Chiang Mai areas. Objectives: To determine accuracy of human-sighted visual range to estimating short-term Particulate Matter (PM) concentration Methods: A retrospective study was conducted purposively among hospitals and Public Health Office at 25 districts in Chiang Mai province where DustBoy air measurement devices were installed and reported air quality including PM2.5, PM10, temperature and relative humidity. The human-sighted visual range (Hr) were reported by trained health staff following the manual applied from “Wildfire Smoke, A Guide for Public Health Officials”. The Hr were reported into six color levels: blue, green, yellow, light orange, dark orange, and red., three times per day in morning (9.00), afternoon (13.00) and evening (16.00). Data was collected between April and May 2018. Both data were matched according to the date and time, excepted data with relative humidity exceeded 65% were excluded. Descriptive statistics described general data and Cohen's kappa statistics analyzed the accuracy of Hr. Results: Hr accuracy for PM10 was at a good level (79.21%) while Hr for PM2.5 was not useful (26.49%). Conclusion: Human-sighted visual range could be applicable for PM10 assessments for community. However, it would not be effective in early-morning, twilight-hours, rainy day, cloudy or humidity >65%. Moreover, personal experience and judgment should be of concern.