Nepal Cookstove Trials

Summary of Environmental Concentrations in Nepal

Cookstove

Phase I Study

Nepal Cookstove Intervention Project – Phase I

• Cluster-randomized, modified step-wedge trial nested in Nepal Nutrition Intervention Project – Sarlahi (NNIPS)

– Evaluate the effect of using enhanced, ventilated cookstoves to improve indoor air quality for maternal and child health

– Continuous PM, CO, and temperature/humiditywere measured before and after new stove installation in eligible households for ~24hs

– 3,356 eligible households for pre-intervention

– 3,188 eligible households for post-intervention

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Stoves Selected for Main Trial

Improved Stove

(Envirofit G3300/G3355)

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Traditional Mud Stove

Environmental Sampling

• PM – DataRAM pDR-1000 (passive mode)• CO – LASCAR data logger• Temperature and humidity - HOBO U10 Data Logger • Placed ~1 meter in front of the stove and ~1.5 meters

off the floor• Sampling started ~3pm and ended around noon the

next day with data logged every 10s

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http://tinyurl.com/low5k4w http://tinyurl.com/kpmnu3f http://tinyurl.com/mas9ukj

Quality Control

• Qualitative assessment

• Humidity adjustment and gravimetricequivalent to PM2.5 for nephelometric instrument

– Adjust for overestimation of PM concentration due to changes in particle size distribution with increasing humidity

– Account for characteristic differences between calibrated standard and local PM

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Data Processing

• Data smoothing and aggregation into average of 5 minutes

• Differentiate 24-h average household air pollution into stove-influenced (SI) and non-stove-influenced (non-SI) periods

– Algorithm based on three constants and considered variation across households

Stove-Influence Algorithm

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• SI concentrations calculated through 27 combinations of coefficients yielded high correlations

Pre-Intervention

Summary of Pre-intervention Exposure

• 2966 measurements for PM2.5, and 2002 measurements for CO collected between March 2010 and March 2011

• Median sampling time 21.7 h (IQR, 20.9—22.1h)

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Diurnal Variation and SI Period

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Monthly Variation

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Correlation of PM2.5 and CO

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Stove Effect on Concentrations

Pre- and Post-Intervention Daily Average Concentrations

Pollutant # HH Mean (95% CI) Median (IQR)

Pre-SI PM2.5 (μg/m3) 2963 1380 (1336, 1425) 1085 (620, 1763)

CO (ppm) 2011 11.0 (10.6, 11.4) 8.1 (4.6, 14.5)

Post-SI PM2.5 (μg/m3) 2752 936 (895, 978) 654 (350, 1166)

CO (ppm) 1848 6.7 (6.4, 7.1) 4.1 (2.2, 8.2)

Summary of Stove Effect

+-Lower and upper 95% CI of regression coefficient estimate.

Summary of Stove Effect in Percentage Change

Phase II Study

Nepal Cookstove Intervention Project – Phase II

• Randomized trial nested in Nepal Nutrition Intervention Project – Sarlahi (NNIPS)– Evaluate the effect of using enhanced, ventilated

cookstoves and LPG stove to improve indoor air quality for maternal and child health

– Continuous PM, CO, and temperature/humiditywere measured after enhanced and LPG stoves installed in eligible households for ~24hs

– Same sampling equipment, quality control and data processing as Phase I study

– 926 eligible households for enhanced cookstove

– 967 eligible households for LPG cookstove

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Enhanced and LPG Cookstove Daily Average Concentrations

Pollutant # HH Mean (95% CI) Median (IQR)

Enhanced

cookstove

PM2.5 (μg/m3) 659 885 (810, 959) 618 (299, 1104)

CO (ppm) 526 5.5 (5.0, 6.0) 3.4 (1.3, 7.6)

LPG

cookstove

PM2.5 (μg/m3) 661 443 (4-3, 482) 268 (128, 594)

CO (ppm) 522 1.7 (1.5, 1.9) 1.0 (0.6, 1.8)

Stove Effect from Linear Regression Model

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Pollutant concentration=β0+β1×Stove Type+β3×S(Date,3)

S: natural cubic spline with 3 degree of freedom to account for seasonal change.

Stove effect was defined as the reduction in pollutant concentration associated with stove type change

LL Stove Effect UL

(Absolute Change)

LL Stove Effect UL

(Percentage Change) (%)

P-value

PM2.5 (μg/m3) 364 444 523 41 50 59 <0.001

CO (ppm) 3.2 3.8 4.3 59 69 79 <0.001

Linear Regression Models—PM2.5

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Linear Regression Models—CO

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Household Characteristics (N=2966)

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*Percentage among households with non-missing values. Households with missing household

characteristics are not statistically different from the others in exposure

Linear Regression Models—PM2.5

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Linear Regression Models—CO

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Summary of Pre and Post Measurements

• Environmental measurements collected between March 2010 and July 2012

• 2461 households had both pre and post measurements for PM2.5, 1128 households had both measurements for CO

Summary of Pollutants from Pre and Post Stove Installation

* SI for stove-influenced; +-Lower and upper 95% CI of regression coefficient estimate.

Stove Effect from Linear Mixed Effect Regression Model

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• Pollutant concentration=β0+β1×Stove Installation+β2×Rainfall+β3×S(Date,8)– Fixed effect: stove installation, natural spline of date with 8 degree of freedom, rainfall. – Radom effect: household, cluster.

• Stove-installation effect is defined to be the predicted difference in average daily HAP for a one-year period after the post-installation measurements began (April, 2011 – March, 2012) to the corresponding one-year period immediately before stove installation (April, 2010 – March, 2011).

Summary of Phase II Measurements

• Both enhanced stoves and LPG stoves were installed between March 2013 and June 2013

• Environmental measurements collected between June 2013 and February 2014

• 659 households with enhanced cookstove had environmental measurements, 661 households with LPG cookstove had environmental measurements

Figure. CO and PM2.5 concentrations for LPG cookstoves

Summary of Pollutants from Enhanced and LPG Stove