Understanding Exposure to Air Pollutants in the Built Environment

Transcription

1 Understanding Exposure to Air Pollutants in the Built Environment William W Nazaroff Civil & Environmental Engr. Dept. University of California, Berkeley California, USA COBEE 1 st International Conference on Building Energy and Environment Dalian, China July 2008

2 Issue and objective Major concern about air pollutants: Health effects Health effects don t occur without exposure Most air pollutant exposure occurs indoors Built environments are numerous, diverse, and complex Important to quantify indoor exposures to air pollutants Need a systematic approach that fosters understanding Goal: Build a mechanistic understanding of air pollutant exposures indoors. Caveat: This presentation is mostly limited to inhalation exposure. Dermal uptake and ingestion are also important for some pollutants.

3 Air-pollution source-to-effects paradigm emissions concentration exposure intake dose effects After KR Smith, Annual Review of Energy and the Environment 18, 529, 1993.

4 Concepts in exposure science (for air pollutants) Qualitative idea: Exposure intersection in space & time between pollutants & people Some quantitative measures related to exposure (dimensions): Concentration species mass per air volume (M/L 3 ) Exposure concentration concentration in breathing zone (M/L 3 ) Exposure time-integral of exposure concentration [(M/L 3 )-T] Intake mass inhaled = exposure breathing rate (M) Uptake mass retained = intake retention fraction (M) See also: V Zartarian et al., J Exposure Analysis & Environmental Epidemiology 15, 1, 2005.

5 Exposure and intake are related to concentration Let X(t 1 -t 2 ) be exposure for t 1 to t 2 Let I(t 1 -t 2 ) be the intake for t 1 to t 2 Let Q B be volumetric breathing rate Let C x (t) be exposure concentration X(t 1 " t 2 ) = I(t 1 " t 2 ) =.4 t 2#.2 C x (t ) dt t 1 t 2$ Q B (t )#C x (t ) dt t 1 concentration (mg per cubic meter) exposure concentration versus time area =! C(t) dt time (min) In this example, X(0-100 min) = 47 mg m -3 min; if Q B = 0.01 m 3 min -1, then I(0-100 min) = 0.47 mg

6 Exposures in the built environment Exposure is inherently complex many influencing factors difficult to measure incompletely understood Important factors that affect exposure pollutant/source characteristics building characteristics human characteristics Need tiered approach simple methods for rapidly estimating magnitudes more complex methods for detailed assessment when needed

7 Pollutant and source factors affect exposure Dynamic behavior of pollutants vary by class inorganic gases (CO, NO x, O 3, SO 2, NH 3, ) VOCs (some sorptive interactions) SVOCs (strong sorption & persistence) particulate matter (size-dependent behavior) bioaerosols Source characteristics indoor emissions or intrusion from outdoors episodic or persistent localized or distributed

8 Building factors affect exposure Ventilation system mixing or displacement flow natural/infiltration or mechanical air filters ventilation rate Intrazonal mixing and interzonal airflows Building configuration (size, layout) Building & furnishing materials (emissions) Indoor surfaces (sorption & surface chemistry)

9 Human factors affect exposure Occupancy occupant density temporal pattern Age & activity level (breathing rate) Activity (emissions)

10 An exposure efficiency metric: Intake fraction (if) emissions concentration exposure intake dose effects emissions concentration exposure intake (linear relationship, usually) intake fraction = intake emissions See also: DH Bennett et al., Environmental Science & Technology 36, A206, 2002.

11 Intake fraction: Some attributes Intake fraction (if) is dimensionless Focuses on source-receptor relationships Emphasizes effect of proximity Can simplify exposure assessments If intake fraction & emissions are known: I ~ if " E

12 if for indoor emissions: nonreactive & well-mixed Q B Q =! V v if ~ Q B Q if is species independent for nonreactive pollutants Typical values (US residential or commercial bldgs): Q B ~ 0.5 m 3 /h per person Q ~ 130 m 3 /h per person if ~ 4000 per million for release into an occupied bldg. if is independent of time pattern of emissions, if occupancy and ventilation rate are constant. Source: WW Nazaroff, Building and Environment 43, 267, 2008.

13 Intake fraction: Typical values & Rule of 1000 A typical pollutant release indoors is ~ 1000 times as effective in causing human exposure as the same release to outdoor air. (Smith, 1988). moving vehicle, 1-4 occupants residence, 1-5 occupants "rule of 1000" ground-level line source elevated point release well-mixed air basin , ,000 intake fraction (per million) Figure from ACK Lai et al., J Air & Waste Management Association 50, 1688, 2000.

14 Some exposure examples 1. Particles of outdoor origin 3. Byproducts of ozone-initiated indoor surface chemistry 2. Air pollutants from cleaning products

15 1. Indoor particle dynamics and exposure Seek mechanistic, quantitative understanding of relationship between governing processes and exposure or intake. Emissions

16 Particle size varies tremendously; All are small ultrafine fine (PM 2.5 ) accumulation coarse Particle diameter (micrometer = µm) Ultrafine particles: behave like large gas molecules Coarse particles: gravitational settling and inertia dominate Accumulation particles: too big to diffuse, too small to settle

17 Material-balance model for indoor particles C o Q S Q Q N L " S P V C i! E Q + Q + Q S N L Q F " F Strong dependence on particle diameter: C o, P, E, η S, η F, β Strong dependence on time: C o, E, Q S, Q N, Source: WW Nazaroff, Indoor Air 14 (Suppl. 7), 175, 2004.

18 Filtration efficiency (η F, η S ): Characteristic U shape ultrafine accumulation coarse ASHRAE, 65% dustspot efficiency filter Source: WW Nazaroff, Indoor Air 14 (Suppl. 7), 175, 2004.

19 Particle penetration through building cracks (P) ultrafine coarse accumulation d = 1 mm; z = 10 cm; P = 4 Pa Source: DL Liu and WW Nazaroff, Atmospheric Environment 35, 4451, 2001.

20 Particle deposition onto indoor surfaces (β) coarse accumulation ultrafine Source: WJ Riley et al., Environmental Science & Technology 36, 200, 2002.

21 Results: Indoor proportion of outdoor particles Central air: Continuous fan (Q R /V = 4 h -1 ); furnace filter; Q L /V = 0.75 h -1. Typical ventilation: Q L /V = 0.53 h -1. Office: Q S /V = 0.73 h -1 ; Q R /V = 3 h -1 ; Q L /V= 0.25 h -1 ; ASHRAE 40% or 85% dust-spot filter for S & R. Source: WJ Riley et al., Environmental Science & Technology 36, 200, 2002.

22 Annual US intake of PM 2.5 of outdoor origin I ~ C o "Q B " US Conditions [( IPOP res " f res )+ ( IPOP ofc " f ofc )+ f out ] C o ~ 10 µg m -3 Q B ~ 4000 m 3 y -1 IPOP res ~ (estimated IPOP for residential PM 2.5 ) f res ~ 0.69 (average fraction of time at home) IPOP ofc ~ (estimated IPOP for nonresidential PM 2.5 ) f ofc ~ 0.18 (average fraction of time indoors, not at home) f out ~ 0.13 (time spent outdoors or in transport microenvironments) I ~ mg per person per year I ~ 6-10 t/y for US population (300 million)

23 2. Cleaning products and air pollutant exposure Asthma linked to cleaning Some cleaning solvents are toxic 2-butoxyethanol 2-hexyloxyethanol Terpenes: solvents and fragrances Terpenes + ozone chemistry: aldehydes particles and more d-limonene

24 Emissions characterization experiments (*) Product Constituents full-strength spray, wipe full-strength scrub, rinse dilute (floor mop) Glass cleaner (GLC-1) 2-butoxyethanol 2-hexyloxyethanol General purpose cleaner (GPC-1) pine oil: terpenes, terpene alcohols General purpose cleaner (GPC-2) 2-butoxyethanol General purpose cleaner (GPC-3) 2-butoxyethanol General purpose cleaner (GPC-4) 2-butoxyethanol, limonene (*) Seventeen simulated uses in 50 m 3 chamber ventilated at 0.5 ach.

25 Concentration patterns: 2-butoxyethanol peak levels are ~ mg/m 3 concentrations at 4-24 h are higher with towels peak occurs min after mopping Source: BC Singer et al., Indoor Air 16, 179, Simulated uses in 50 m 3 chamber with 0.5 ach.

26 Fractional emissions vary among compounds pine-oil based cleaner (GPC-1) Key findings: 1. towel removal lowers emissions 2. emitted fractions are lower with dilute use 3. terpene alcohols volatilize less than terpene hydrocarbons Source: BC Singer et al., Indoor Air 16, 179, Simulated uses in 50 m 3 chamber with 0.5 ach.

27 Secondary pollutants from terpenes + ozone Thirteen simulated use experiments. V = 50 m 3 ; 1 ACH Ozone in supply air at 120 ppb in seven experiments. Primary emissions: OH O O O OH OH O O OH

28 Byproduct formation with ozone (PM, HCHO, OH) 300 B Exp. C: OOD PM 1.1 concentration (µg m -3 ) A C B A C Exp. G: POC Exp. J: AFR d-limonene ozonolysis is particularly effective in producing secondary PM 24-h PM2.5 std (ambient air) time (h) Source: BC Singer et al., Atmospheric Environment 40, 6696, 2006.

29 Cleaning-product exposure analysis Scenario Routine cleaning by occupant Professional domestic cleaner Clean surfaces in small bathroom Clean all interior windows with low ventilation Air freshener + O 3 in bedroom Cleaning with high outdoor O 3 Result Exposure well below reference levels Formaldehyde exceeds NSRL, SOA exceeds annual PM 2.5 standard Exceed acute REL for 2-butoxyethanol Approach/exceed REL for 2- butoxyethanol Exceed formaldehyde NSRL Daily average is 25% of PM 2.5 limit Acronyms: NSRL no-significant risk level; SOA secondary organic aerosol; REL reference exposure level; PM 2.5 particulate matter smaller than 2.5 micrometers in diameter.

30 3. Estimating attributable intake: O 3 byproducts What? Mass inhaled by US population of the airborne byproducts of ozone-initiated indoor chemistry Why? Provides perspective on the relative importance of this source for causing pollutant exposure How? Approach 1: Estimate based on exposure concentration Approach 2: Estimate based on intake fraction Source: WW Nazaroff and CJ Weschler, to be presented at Indoor Air 2008, Copenhagen, Denmark.

31 Products of ozone-initiated organic chemistry Radicals: OH, HO 2, RO, RO 2 Peroxides: H 2 O 2, hydroperoxides, organic peroxides Short-lived organics: ozonides, peroxyhemiacetals, α-hydroxy hydroperoxides Stable organics (*): aldehydes, ketones, diols, acids Nazaroff & Cass 1986; Weschler & Shields 1996, 1997; Sarwar et al., 2002 Li et al., 2001; Fan et al., 2003; Atkinson & Arey, 2003 Tobias and Ziemann 2000; Tobias et al. 2000; Fick et al., 2003; Atkinson & Arey, 2003 Finlayson-Pitts & Pitts, 2000; Glasius et al., 2000; Yu et al., 1998, 1999; Atkinson & Arey, 2003 (*) Only these are routinely measured and therefore included in assessment. Courtesy: CJ Weschler

32 Product yields: Experiments in aircraft cabin Y ~ 0.3 moles of stable byproducts formed per mole of O 3 consumed Source: CJ Weschler et al., Environmental Science & Technology 41, 6177, 2007.

33 Attributable intake: O 3 indoor surface chemistry Approach 1: I p ~ C p " P " B Ozone-initiated byproducts from indoor surface reactions # P & C p ~ MW p " F "% Y O3,out (" k ~ 37 µg m*3 $ RT ' k + ) MW p = molecular weight of product ~ 100 g/mol F = fractional yield ~ 0.3 Y O3,out P/RT = avg. outdoor ozone conc. (35 ppb) ~ mol m -3 k = surface loss rate for ozone indoors ~ 3 h -1 λ = air-exchange rate ~ 0.5 h -1 P ~ 300 million B = 4000 m 3 person -1 y -1 I p ~ 45 t/y

34 Attributable intake: O 3 indoor surface chemistry Approach 2: I p ~ if " E E ~ F " MW p MW O3 "C O3,in "v d " S V "V p " P ~ 4,700 t/y F = fractional yield ~ 0.3 mol product per mol O 3 consumed MW p /MW O3 = molecular weight ratio (product/ozone) ~ 2 C O3,in = average indoor ozone concentration (5 ppb) ~ 10 µg m -3 v d = ozone surface deposition velocity ~ 1 m/h S/V = building surface-volume ratio ~ 3 m -1 V p = occupied building volume per person ~ 100 m 3 person -1 P = population ~ 300 million if ~ 4000 per million I p ~ 20 t/y

35 US intake: ambient sources, ETS, O 3 chemistry Source: WW Nazaroff and BC Singer, J Exposure Analysis & Environmental Epidemiology 14, S71, 2004.

36 Future challenges: I. Near-field indoor exposures Detailed airflow studies point to the potential importance of near-head chemistry, chemistry on clothing, and chemistry on floors affecting exposure. Reference: S Zhu et al., Building and Environment 40, , 2005.

37 Future challenges: II. SVOCs Is direct air-to-skin transport an important exposure pathway for indoor SVOCs? Model-measurement comparison: predictions for direct air-to-skin partitioning and measurements from skin wipes. Reference: CJ Weschler and WW Nazaroff, Atmospheric Environment (submitted) 2008.

38 Closing remarks emissions concentration exposure intake dose effects Understanding indoor exposures is essential to promote economical & healthful built environments. Mechanistic framework based on physical science is key to generalizing understanding from empirical evidence. Public health and well-being can benefit from such efforts. Rapid progress is possible with reasonable effort.