Ultrafine and Fine Particulate Matter Inside and Outside of Mechanically Ventilated Buildings.

Shelly Miller,John Zhai,Darin Toohey,Nick Facciola

doi:10.3390/ijerph14020128

Abstract

The objectives of this study were to measure levels of particulate matter (PM) in mechanically ventilated buildings and to improve understanding of filtration requirements to reduce exposure. With the use of an Ultra High Sensitivity Aerosol Spectrometer and an Aerodyne Mass Spectrometer, ultrafine (0.055–0.1 μm) and fine (0.1–0.7 μm) indoor and outdoor PM was measured as a function of time in an office, a university building, and two elementary schools. Indoor particle levels were highly correlated with outdoor levels. Indoor and outdoor number concentrations in Denver were higher than those in Boulder, with the highest number concentrations occurring during summer and fall. The ratio of indoor-to-outdoor (I/O) PM was weakly but positively correlated with the amount of ventilation provided to the indoor environment, did not vary much with particle size (ranged between 0.48 and 0.63 for the entire size range), and was similar for each period of the week (weekend vs. weekday, night vs. day). Regression analyses showed that ultrafine indoor PM baseline concentrations were higher at night from nighttime infiltration. A lag time was observed between outdoor and indoor measurements. Weekday days had the shortest lag time of 11 min, and weekend nighttime lags when the HVAC was not in use were 50 to 148 min. Indoor-outdoor PM concentration plots showed ultrafine PM was more correlated compared to fine, and especially when the HVAC system was on. Finally, AMS data showed that most of the PM was organic, with occasional nitrate events occurring outdoors. During nitrate events, there were less indoor particles detected, indicating a loss of particulate phase nitrate. The results from this study show that improved filtration is warranted in mechanically ventilated buildings, particularly for ultrafine particles, and that nighttime infiltration is significant depending on the building design.

Highlights

Because people spend upwards of 85% of their time indoors, it is widely recognized that a significant portion of total personal exposure to particulate matter (PM) occurs in indoor environments.Roughly 80% of the time indoors is spent in residences, while the other 20% is spent in offices, restaurants, schools, and other indoor locations that are mostly mechanically ventilated buildings.Indoor particle concentrations are often lower in mechanically ventilated buildings compared to outdoor particle concentrations, since most buildings have some filtration in their ventilation systems, and there are limited indoor sources [1,2,3,4]
The air exchange rates (AER) for the teacher’s lounge at the Boulder school was exceedingly high, possibly due to a design airflow rate that accounted for cigarette smoking, as the building was built in 1971
Each air exchange rate test was conducted during the day when the HVAC was running, except for the single overnight run at the Boulder school

Summary

Introduction

Because people spend upwards of 85% of their time indoors, it is widely recognized that a significant portion of total personal exposure to particulate matter (PM) occurs in indoor environments.Roughly 80% of the time indoors is spent in residences, while the other 20% is spent in offices, restaurants, schools, and other indoor locations that are mostly mechanically ventilated buildings.Indoor particle concentrations are often lower in mechanically ventilated buildings compared to outdoor particle concentrations, since most buildings have some filtration in their ventilation systems, and there are limited indoor sources [1,2,3,4]. Because people spend upwards of 85% of their time indoors, it is widely recognized that a significant portion of total personal exposure to particulate matter (PM) occurs in indoor environments. 80% of the time indoors is spent in residences, while the other 20% is spent in offices, restaurants, schools, and other indoor locations that are mostly mechanically ventilated buildings. Indoor particle concentrations are often lower in mechanically ventilated buildings compared to outdoor particle concentrations, since most buildings have some filtration in their ventilation systems, and there are limited indoor sources [1,2,3,4]. This research was conducted to better understand the factors that influence PM in mechanically ventilated buildings. Res. Public Health 2017, 14, 128; doi:10.3390/ijerph14020128 www.mdpi.com/journal/ijerph

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