Rural and urban exposure to indoor air pollution

Sumeet SaksenaEast West Center

Honolulu

Alternative title: Satisfying the curiosity of the ambient air pollution

experts about IAP• Principle used: do not preach to the

converted• What do we know and what do we not

know about IAP related human exposures?

• Why we do what we do?

Basics of human exposure assessment

• Whose exposure?– Infants, children, adults (women?), elders, etc.– Influenced by health outcome focus– Implications on protocols (breathing zone, activity

patterns, etc)

• Where is the exposure happening?– Indoors (kitchen, living room), Outdoors (yard, near

house, far from house)

• Duration of exposure?– High concentration short duration exposure– Low concentration long duration exposure

Exposure assessment: direct approach

• Personal monitoring for 24 hours or lesser

Exposure assessment: indirect approach – micro-environmental

modeling• Identify major microenvironments

– Indoors during cooking– Indoors non-cooking (day vs. night)– Outdoors (near ambient)

• Daily exposure is time weighted average of area levels (breathing height) in these microenvironments

Typical levels of key pollutants related to cook-stoves (wood fuel)

Pollutant Cooking time average

24-hour average

PM10 (μg/m3) 520-1200 650-2300

PM < 5 (μg/m3)

850-1500 800-3500

CO (mg/m3) 10-50 4-60

Typical levels of key pollutants related to cook-stoves

(kerosene/gas)Pollutant Cooking time

average24-hour average

PM10 (μg/m3) 200-760 170-500

PM < 5 (μg/m3)

70-170 80-130

CO (mg/m3) 3-10

Typical levels of key pollutants related to cook-stoves: key

messages• Anomalies partly due to lack of

uniformity in measurement protocols• Background PM levels are high

Particulate matter size distribution

• Recent study in Costa Rica indicated two peaks at 0.7 and 2.5 microns

• In lab studies, unimodal aerosol size distributions observed with mass median aerodynamic diameters of 0.5-0.8 microns

Trends in measurement methods

• PM: gravimetric– Low-flow pumps for area/stationary or

personal sampling– Medium-flow pumps for area/micro-

environmental sampling– Cyclones for 3.5, 4, and 5 microns– Impactors for 2.5 and 10 microns– Advantage: standard methods available (e.g.

NIOSH 0600), further chemical analysis– Disadvantage: cost (~ $1500 per kit), high

QA/QC skills, electricity in the field, etc.

Trends in measurement methods (cont.)

• PM: real time– Based on optical scattering/ ionization.

Very few studies so far– Advantage: real time data, some makes are

inexpensive (UCB monitor), multi-stage size cut-offs

– Disadvantages: commercial access difficult, some models cannot be used in personal mode, particle size-cut off convention different from traditional conventions.

Trends in measurement methods (cont.)

• CO– Potentiometric dosimeters: standard,

durable, expensive– Diffusion tubes: cheap, 25% error

Spatial variations

• Why study?– Whose exposure? – Defining the breathing zone

• Within the kitchen variations– Horizontal : distance from stove, but being far

is not necessarily safer – depends on fuel, stove and ventilation conditions

– Vertical variations: smoke hangs at about 4 feet• Inter-room variations

– Cook moves around– Others in the family

Temporal variations

• Across meals• Day-to-day variations: mixed results so

far• Seasonal variations: few studies,

changes in type of fuel, cooking activity, weather and ventilation

• Few studies conducted with long sampling duration (e.g. one week), but short term measurements not made simultaneously, so cannot conclude

Impacts of stove interventions

• Type 1 studies: cross-sectional designs– Early studies in India and Nepal led to inconclusive

results due to design weaknesses (confounding)– Modest benefits for TSP, better for CO– Hoods more effective– Problems due to neighbours’ smoke and background

levels

• Type 2 studies: before-and-after comparisons– PM reductions of 40-60%– Area levels reduction > personal levels reduction– Study in Kenya found hoods far more effective, and

windows ineffective

Correlations between and among pollutants

• Why study this?– Identify simple and inexpensive proxy indicators

for PM– Simplify personal monitoring

• Correlation between CO and PM (co-located sampling)– Degree of correlation higher over longer periods of

time as compared to shorter periods– As PM size decreases correlation with CO

increases– Mixed results across studies. Degree of correlation

depends on stove, fuel, ventilation factors, etc.

Correlations between and among pollutants (cont.)

• Correlation between area and personal sampling– Mixed results across studies– Situation specific

Other major explanatory factors

• Recent studies have provided evidence of the important role of– Type of house– Location of kitchen– Kitchen architecture– Ventilation

• There is an urgent need to have standard definitions for the above parameters (e.g. what is open cooking?)

Role of time activity patterns

• Obvious: more time spent cooking greater the exposure

• Not so obvious: Interventions and natural transitions not only change emissions but may impact on activity patters and behaviour. The NET impact on exposure can be positive, negative or zero.

Exposure across fuel groups: Delhi slum case study

• Mean daily exposure not significantly different between wood and kerosene users– More meals, more items, longer meals =

longer cooking times in kerosene houses– Kerosene users cook indoors, wood users

outdoors– Infants of kerosene users near stove

longer

Exposures in urban/peri-urban areas

• Concentration levels during cooking same as in rural areas –same fuels, stoves, small kitchens

• Exposure to PM due to cooking as a fraction of daily exposure

• > 75% in rural areas• 10-20% in urban areas

Exposures in urban/peri-urban areas (cont.)

• Dense housing implies– Smoke from one house infiltrates another

house– High near-ambient levels (> 500 ug/m3

for PM5)– Need community-wide interventions– Cluster of houses act as an area source of

ambient air pollution at micro-urban scales

– Indoor-outdoor relationships are complicated and not well studied

IAP exposures and epidemiology

• Only one study (Kenya) quantified the link between exposure and incidence of ALRI– Concave relationship– Rate of increase declining above 11-2 mg/m3

• Highlighted the role of short term peaks• Elevated levels occur during fire ignition

(especially for coal and charcoal) and fire tending

• There is a need to have standard sampling durations (15 minutes, meal time, 24 hour?)

Key research questions/issues for the future

• PM size distribution under field conditions

• Correlation between area and personal sampling

• Quantifying the impact of housing and ventilation variables

• Indoor-outdoor relationships in urban/peri-urban areas

• Measurement of acute exposures

Key issues for aid agencies for the future

• Development of simple and inexpensive methods and protocols

• Identification of other types of interventions in addition to improved stoves

• Harmonization of methods• Training of NGO trainers • Creating repositories of instruments,

Technical Backup Units (linked to NGOs) with advanced infrastructure