Dynamics of particle size and concentration indoors: A building science perspective. Jeffrey Siegel

Transcription

1 Dynamics of particle size and concentration indoors: A building science perspective Jeffrey Siegel jeffrey.siegel@utoronto.ca

2 What governs the dynamics of particle size and concentration indoors? There are different important sources and sinks for particles indoors. The building affects most of the important source and sink processes.

3 What We Know: Source Characteristics Size distribution of many indoor aerosols Combustion sources (cooking, smoking, other) Resuspension from indoor activities Secondary organic aerosol Penetration from outdoors Misc. sources

4 Example: Cooking Wallace et al. (2008) Environ. Sci Tech.

5 What We Know: Sink Characteristics HVAC Air Cleaning Ventilation and Leakage Portable Air Cleaning Deposition

6 Example: Filtration Hanley et al. (1994) Indoor Air Stephens and Siegel (2013) Indoor Air

7 Emerging Knowledge 1. Impact of Building Surfaces 2. Impact of HVAC Systems 3. Heterogeneity of Indoor Concentrations 4. Impact of Non-particle Constituents

8 Building Surfaces Buildings have a lot of surface area Buildings are an amazingly diverse collection of surfaces Indoor surfaces are soiled chemically and biologically We don t see many (most?) relevant surfaces Surfaces interact with aerosols in meaningful ways

9 Surfaces: Deposition The significant effect of particle size and room conditions on deposition loss rates argues against using a single first-order loss-rate coefficient to represent deposition for integrated mass measurements (PM 2.5 orpm 10 ). T.L. Thatcher et al. / Atmospheric Environment 36 ( 2002) Lai and Nazaroff (2000) Aerosol Sci. Tech. Large variation in measured and modeled deposition rates: e.g., PM 2.5 and PM 10 study are also presented (Lai and Nazaroff, 2000). The two traces are intended to approximately span expected conditions for ordinary indoor environments: surfaceto-volume ratio (S=V ¼ 22 4m 2 /m 3 ), turbulence intensity (u ¼ 0:32 3cm/s), and specific gravity of the particles (sg ¼ 1:02 2:5). Fig. 6 reveals several important points. First, particle size is seen to be an important factor influencing deposition rates. For example, the central tendency of the experimental data shows an increase in deposition rate from B 0.1h 1 for 0.2mm particles to B 1h 1 for 2.5 mm particles. This large dependence on size calls into question the utility of using a single loss-rate coefficient for a mass-integral measure such as PM 2.5. Second, for any given particle size, the experimental loss-rate data exhibit a large degree of variability. On the whole, this variability is considerably larger than the factor of 3 found in the current study. For example, for 0.2 mm particles, experimental data vary by a factor of B 100, from B 0.01 to B 1h 1. With respect to assessing human exposure, removal by deposition always competes with removal by air exchange, which seldom occurs at a rate o 0.1h 1. Thus, one might argue that understanding the causes of deposition rate variability at levels below 0.1h 1 are of academic interest Afshari and Reinhold (2008) Indoor Built Environ. Fig. 5. Particle deposition loss-rate coefficients as a function of particle size at each furnishing level. Curves represent the four air flow conditions: without fans, 5.4, 14.2 and 19.1cm/s (mean core airspeed). Thatcher et al. (2002) Atmos Environ

10 Surfaces: Resuspension ded by: [University of Toronto Libraries] 6:35 cis in England and Wales Registered Number: Registered office: Mortimer House, London W1T 3JH, UK Qian and Ferro (2008) Aerosol Sci. Tech Aerosol Science and Technology Publication details, including instructions for authors and subscription information: Mukai et al. (2009) Aerosol Sci. Tech Monolayer and Multilayer Particle Deposits on Hard Surfaces: Literature Review and Implications for Particle Resuspension in the Indoor Environment Brandon E. Boor a, Jeffrey A. Siegel a b & Atila Novoselac Boor et al. (2013) Aerosol Sci. Tech a a Department of Civil, Architectural, and Environmental Engineering, Cockrell School of Engineering, The University of Texas at Austin, Austin, Texas, USA b Department of Civil Engineering, The University of Toronto, Toronto, Ontario, Canada Accepted author version posted online: 16 Apr 2013.Published online: 13 May Kassab et al. (2013) Aerosol Sci. Tech

11 HVAC Systems Forced air systems are ubiquitous ~100% of commercial buildings in US ~80% of residential buildings (66% in America Jr.) Affect indoor particles Filtration (run time, volumetric flow rate) Ventilation (mechanical ventilation, impact on leakage) Deposition and resuspension (air velocities and turbulence) Components act as a source (direct or indirect) or sink Change in environmental conditions Mixing

12 HVAC Systems: Runtime Reference Location Sample Size Thornburg et al. (2004) Atmos. Environ. NC FL 26 9 Fractional On-Time (%)(mean ± s.d.) 6.1 ± ± 11 Stephens et al. (2011) Bldg. Environ. TX ± 25 Cetin and Novoselac (2015) Energy Bldg. TX ± 2.4 Cetin and Novoselac (2015) Figure 3a

13 flow rate run time volume λ i = 0.44 hr -1 β 2.5 = 0.74 hr -1 β 10 = 3.87 hr -1 base case is MERV 3

14 Heterogeneity: Exposure to indoor Ubiquity of well-mixed assumption in exposure assessments sources Acevedo-Bolton et al. (2014) Indoor Air

15 Heterogeneity: Sinks Air Cleaner Effectiveness, H μm particles Time (min) Air Cleaner Effectiveness, H μm particles Time (min) Air Cleaner a CADR = 50 m /hr Air Cleaner b CADR = 500 m /hr 3 3 in Room 1 in Room 1 in Room 2 in Room 2 in Room 3 in Room 3 Novoselac and Siegel (2009) Bldg. Environ.

16 Heterogeneity: Importance for Exposure Rim and Novoselac (2010) JOEH Rim and Novoselac (2010) Bldg. Environ.

17 Knowledge Gaps Our knowledge of fundamental characteristics of buildings is insufficient to fully understand indoor aerosol exposure.

18 Knowledge Gap 1: HVAC Characterization Riley et al (2002) ES&T = 4/hr Chen et al. (2012) Epidem. = 3.1/hr

19 Knowledge Gap 2: Ventilation Dynamics Carrilho et al. (2015) Energy Bldg.

20 Knowledge Gap 3: Sink Dynamics Ref: Lehtimäki et al. (2002) ASHRAE RP-1189 Report Montgomery et al. (2015) Aerosol Sci. Tech

21 Knowledge Gap 4: Unseen Surfaces and Spaces A short list of interstitial and buffer spaces Inside walls/ceilings/floors Attics Crawlspaces Basements Kneewalls Garages

22 Addressing Knowledge Gaps Canada s long-form census is back for 2016 Just a day after taking office, the Liberal government announced Thursday that the mandatory long-form census axed by the Conservatives in 2010 will be reinstated for the 2016 census. Ref: liberals-restore-mandatory-long-form-census.html A really long-form building census Address key building science parameters needed to understand (and mitigate) exposures to particles in buildings Opportunity for citizen science and practitioner science

23 Thank you