Science for Society
Buildings account for a significant fraction of the land area in cities and actively exchange air with their proximate outdoor environments via mechanical ventilation systems. However, the direct impact of buildings on urban air pollution remains poorly characterized. Due to reductions in traffic-associated emissions of volatile organic compounds (VOCs), volatile chemical products, which are widely used inside buildings, have become a major VOC source in urban areas. Indoor-generated VOCs are likely to be an important contributor to the VOC burden of the urban atmosphere, and ventilation systems provide a pathway for VOCs to be released outdoors. Here, we show how modern buildings act as significant emission sources of VOCs for the outdoor environment. Our results demonstrate that future air quality monitoring efforts in cities need to account for direct VOC discharge from buildings in order to capture emerging sources of environmental pollution that can impact the climate and human health.
Summary
Urban air undergoes transformations as it is actively circulated throughout buildings via ventilation systems. However, the influence of air exchange between outdoor and indoor atmospheres on urban air pollution is not well understood. Here, we quantify how buildings behave as a dynamic source and sink for urban air pollutants via high-resolution online mass spectrometry measurements. During our field campaign in a high-performance office building, we observed that the building continually released volatile organic compounds (VOCs) into the urban air and removed outdoor ozone and fine particulate matter. VOC emissions from people, their activities, and surface reservoirs result in significant VOC discharge from the building to the outdoors. Per unit area, building emissions of VOCs are comparable to traffic, industrial, and biogenic emissions. The building source-sink behavior changed dynamically with occupancy and ventilation conditions. Our results demonstrate that buildings can directly influence urban air quality due to substantial outdoor-indoor air exchange.
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Emerging investigator series: primary emissions, ozone reactivity, and byproduct emissions from building insulation materials
Building insulation materials can affect indoor air by (i) releasing primary volatile organic compounds (VOCs) from building enclosure cavities to the interior space, (ii) mitigating exposure to outdoor pollutants through reactive deposition (of oxidants, e.g. , ozone) or filtration (of particles) in infiltration air, and (iii) generating secondary VOCs and other gas-phase byproducts resulting from oxidant reactions. This study reports primary VOC emission fluxes, ozone (O 3 ) reaction probabilities ( γ ), and O 3 reaction byproduct yields for eight common, commercially available insulation materials. Fluxes of primary VOCs from the materials, measured in a continuous flow reactor using proton transfer reaction-time of flight-mass spectrometry, ranged from 3 (polystyrene with thermal backing) to 61 (cellulose) μmol m −2 h −1 (with total VOC mass emission rates estimated to be between ∼0.3 and ∼3.3 mg m −2 h −1 ). Major primary VOC fluxes from cellulose were tentatively identified as compounds likely associated with cellulose chemical and thermal decomposition products. Ozone-material γ ranged from ∼1 × 10 −6 to ∼30 × 10 −6 . Polystyrene with thermal backing and polyisocyanurate had the lowest γ , while cellulose and fiberglass had the highest. In the presence of O 3 , total observed volatile byproduct yields ranged from 0.25 (polystyrene) to 0.85 (recycled denim) moles of VOCs produced per mole of O 3 consumed, or equivalent to secondary fluxes that range from 0.71 (polystyrene) to 10 (recycled denim) μmol m −2 h −1 . Major emitted products in the presence of O 3 were generally different from primary emissions and were characterized by yields of aldehydes and acetone. This work provides new data that can be used to evaluate and eventually model the impact of “hidden” materials ( i.e. , those present inside wall cavities) on indoor air quality. The data may also guide building enclosure material selection, especially for buildings in areas of high outdoor O 3 .
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- PAR ID:
- 10134013
- Date Published:
- Journal Name:
- Environmental Science: Processes & Impacts
- Volume:
- 21
- Issue:
- 8
- ISSN:
- 2050-7887
- Page Range / eLocation ID:
- 1255 to 1267
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Scented wax products, such as candles and wax warmers/melts, are popular fragranced consumer products that are commonly used in residential buildings. As scented wax products are intentionally fragranced to produce pleasant smellscapes for occupants, they may represent an important source of volatile organic compounds (VOCs) to indoor atmospheres. The aim of this study is to evaluate terpene emission factors (EFs) and inhalation intake fractions (iFs) for scented wax products to better understand their impact on indoor chemistry and chemical exposures. Full-scale emission experiments were conducted in the Purdue zEDGE Test House using a variety of scented candles (n = 5) and wax warmers/melts (n = 14) under different outdoor air exchange rates (AERs). Terpene concentrations were measured in real-time using a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS). PTR-TOF-MS measurements revealed that scented candle and wax warmer/melt products emit a variety of monoterpenes (C10H16) and oxygen-containing monoterpenoids (C10H14O, C10H16O, C10H18O, C10H20O), with peak concentrations in the range of 10^−1 to 10^2 ppb. Monoterpene EFs were much greater for scented wax warmers/melts (C10H16 EFs ~ 10^2 mg per g wax consumed) compared to scented candles (C10H16 EFs ~ 10^−1 to 100 mg per g wax consumed). Significant emissions of reactive terpenes from both products, along with nitrogen oxides (NO, NO2) from candles, depleted indoor ozone (O3) concentrations. Terpene iFs were similar between the two products (iFs ~ 10^3 ppm) and increased with decreasing outdoor AER. Terpene iFs during concentration decay periods were similar to, or greater than, iFs during active emission periods for outdoor AERs ≤ 3.0 h^−1. Overall, scented wax warmers/melts were found to release greater quantities of monoterpenes compared to other fragranced consumer products used in the home, including botanical disinfectants, hair care products, air fresheners, and scented sprays.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c9em00024k
