RELATIONSHIPS BETWEEN INDOOR AND OUTDOOR AIR POLLUTION

DAVID BRODAY

Indoor Air Quality and Health – Environmental and Health Fund – 14/9/2021

(Steinle et al., 2015)Indoor Air Quality matters

(not only in countries that use open

fire for cooking and/or heating)

NO2 concentration (ppb) Daily exposure to NO2

(Shafran-Nathan et al., 2018)

Indoor and outdoor air pollutants are subjected to distinct

processes

(Nazaroff et al., Atmospheric Environment, 2003; Weschler, Indoor Air, 2011)

Photochemistry is less importantphoton flux is lower (w/ different spectral distribution).

No precipitation scavenging indoors.

Engineered air cleaning devices only indoors

OutdoorIndoorAttribute

(heterogenous/

homogenous chemistry)

(heterogeneous/ surface

chemistry – faster)

Surface-to-volume ratio

(unlimited)

(limited due to economic

considerations)

Air exchange rate/ fresh

air/ ventilation

summerwinterT

wintersummerRH

Photochemistry

OHO3 Leading oxidant

wet deposition/

scavenging

dry deposition/ HVAC systems

(desorption)

Removal

windhuman activitiesResuspension

I/O ratio References

O3 0.2-0.7 (Weschler, 2000; …)

NOx 0.3-3 (Pitts et al., 1989; Levy et al., 1998; …)

OH ~0.1 (Fan et al., 2003; Fick et al., 2002, 2003; Singer

et al., 2006; Weschler and Shields, 1997; White

et al., 2010)

PM PM10 ~ 0.7

PM2.5 ~1

(Wallace, 1996; Finlayson Pitts and Pitts, 2000;

Abt et al., 2000; Jimenez, 2006)

VOC 2-80 (Brown et al. 1994; Nazaroff et al. 2004; Uhde et

al. 2007; Morrison et al. 2002; Reiss et al. 1995;

Sarwar et al., 2002; …)

IOR

(Chan, 2002)

What affects the

IOR

(PM4 & NOx; classroom in HK)

What affects IOR?(office in HBA at small mechanics shop area)

IOR varies (i.e. is a stochastic variable)

D: 6 - 18

N: 18 - 6

WD: Sun - Thu

WE: Fri - Sat

Diff. Stat. sig.

W: Dec - Feb

T: Mar - Apr, Oct-Nov

S: May - Sep

LW: <2.3 m/s

HW: >2.3 m/s

2.3 m/s = median

Diff. Stat. sig.

LT: <25% percentile

MHT: > 25% percentile

25% percentile = 16.3 oC

Diff. Stat. sig.

Split (24 categories) O3 NOx NO NO2 PM10

DayWinterColdHighWind 1 1 1 0 1

DayWinterColdLowWind 3 2 2 0 2

DayWinterHotHighWind 0 1 1 1 2

DayWinterHotLowWind 1 2 2 1 5

DaySummerHotHighWind 1 1 1 1 1

DaySummerHotLowWind 1 1 2 1 0

DayTransitionColdHighWind 0 2 1 0 2

DayTransitionColdLowWind 0 1 1 1 0

DayTransitionHotHighWind 0 1 1 1 1

DayTransitionHotLowWind 0 2 2 1 1

NightWinterColdHighWind 1 1 3 1 1

NightWinterColdLowWind 0 4 4 2 1

IOR is affected by the pollutant penetration “time constant”

Lag (time points

= 0.5 hrs) when

the highest

correlation was

observed

N,S,MHT

D,S

N,S.LT,HW

D,S,LT,HWD,T,MHT,HW

D,S,MHT,HW

IOR variability

Time seriesreveal that IOR does not tell the whole story

(Chatoutsidou et al., 2015)

PM10PNC

IOR by particle size(office in GR)

Physical drivers that affect IOR

and pollutant transport in built

environments

What affects the IOR?

Physical drivers of IOR and pollutant transport

Tin > Tout

TinTout Tout Tin

Tin < Tout

Pout Pin

Cold air

Hot air

(Reichman & Dubowski, 2020)

Simulation of pollutant transport in a multi-story building

Tin > Tout

TinTout

Pout Pin