UCLA

Introduction: Air pollution is associated with various adverse acute and chronic health outcomes. Indoor air quality is of great concern as people spend a majority of time indoors. To better study indoor pollutants in a community scale, low-cost particulate matter (PM) sensors were installed in a community to collect and monitor PM data.

Objectives: 1. Identify indoor PM sources. 2. Identify and measure effectiveness of indoor PM mitigation measures. 3. Determine the capability of the use of low-cost sensors.

Methods: 18 apartments in the UCLA university village were recruited for the study. Each apartment was installed with one PurpleAir PM sensor. 12 outdoor sensors were installed on the roof of apartment buildings distributed evenly in the village. PM data were collected automatically by the sensors every 80 seconds and were uploaded to PurpleAir website in real time. Recruited residents were asked to complete one activity log to record their indoor activities and one survey for home characteristics, cleaning activities and cooking activities.

Results: Cooking is the most significant indoor PM source, with 28 reported cases and average PM2.5 I/O ratio of 14.3 during cooking hours, the average I/O ratio during non-cooking hours is 1.51. Candle burning is another strong indoor source but with low occurrence frequency. The average PM2.5 I/O ratio during candle burning is 13.08 and during non-burning hours is 1.27. Outdoor and indoor PM2.5 concentration has a strong linear relationship with regression coefficient = 0.35 and R2 = 0.61 when there are no indoor human activities. Natural ventilation can reduce PM2.5 I/O ratio faster after cooking activities. Apartments with air purifier turned on all the time have a significantly lower indoor PM2.5 concentrations and I/O ratios compared to apartments without air purifiers or apartments that use air purifier less frequently. Turning on the fan over stove while cooking can effectively reduce PM levels.

Conclusions: The study shows that various sources of indoor PMs and the effect of indoor PM mitigation measures are detected by the PurpleAir. Indoor PMs are contributed by indoor human activities and transportation from outdoor air. The use of an air purifier is an effective mitigation measure. PurpleAir low-cost sensors are capable equipment in conducting such a community scale study.