Research Triangle Energy Consortium

When was the last time you saw a headline such as this? Probably never. While indulging in a modicum of hyperbole, as you will see, the headline is not too much of a reach. The environment here is that experienced in household air pollution (HAP) and is the direct cause of an estimated 3.6 million deaths annually. Substantial radiative forcing is also expected from the elemental carbon emissions, with the HAP source estimated to provide 20% of the loading worldwide, and a much higher proportion in Asia. Radiative forcing has a direct impact on climate change.

3 billion persons use biomass as a cooking fuel, almost all in low- and middle-income countries (LMIC’s). The biomass is largely the wood of convenience but can also be animal waste (dung). In countries such as the Sub-Saharan Burkina Faso, 95% use biomass for cooking. Improving cookstoves has been a pursuit for decades. While improving efficiency of the stove does reduce the emissions per cooking episode, the overall reduction is not sufficient for a significantly favorable mortality outcome. For a clue regarding the reason for this, consider that the PM_2.5 count can be as high as 600 μg/m3, as compared to the WHO guideline of 35 μg/m3, and the US standard of 12 μg/m3. Some of the “improved” stoves reduce the emissions by 60%. That does not cut it. To make matters worse, the emissions/impact curve is supralinear, meaning the impact curve flattens at high exposures, despite being linear at the very low numbers. This means that the gains are relatively small for exposure reductions from high to moderate numbers.

This relatively recent realization (a 2014 publication) has led to interventions involving complete substitution of the biomass fuel. The leading candidates are alcohols, liquefied petroleum gas (LPG) and electricity. Electricity is not a good idea. Target villages lack electricity for the basic necessities of lighting, fans and cell phone charging, with the occasional refrigerator. Diverting what little is available to cook stoves, when other alternatives exist, is a bad idea. Ethanol is too expensive and in many countries the production would compete with a food use. LPG has become the favored substitute in many countries.

LPG is a mixture of propane, butane, and some larger molecules. It is derived from oil and gas production. It is delivered in pressurized cylinders, typically holding 14.2 kg fuel. The particulate emissions from an LPG stove have been observed to be close to the WHO guideline of 35 μg/m3, compared to up to 600 μg/m3 with traditional fuel and stoves. Many countries have doubled down on this fuel substitution. India has programs for distribution of stoves and substantial subsidies on the fuel.

But the health benefits from this substitution have not been quantified in randomized control trials until recently. Many of these are ongoing. The largest of these is the USD 30 million Household Air Pollution Intervention Network (HAPIN) trial in 3200 households in India, Rwanda, Guatemala, and Peru. In a recent advance in the state of the art in PM_2.5 monitoring, a small wearable device, RTI’s Enhanced Children’s MicroPEM^TM is utilized. This follows the personal exposure on pregnant women, other adult women, and children under 1 year of age. This cohort is the most affected by HAP caused by cookstoves. Carbon monoxide is also measured in the cooking area. Studies have shown that the total PM exposure captured by the wearable monitor is usually less than would be measured in the ambience of the home. In any case, the monitor comes closest to determining what the person breathes and will likely become the standard of practice in trials. The filters in the monitors are archived and the collected PM may be used in in vitro studies to assess the toxicity of the particles.

Even if the health benefits of LPG substitution of biomass are established, issues remain. Almost all the affected LMIC’s are net importers of LPG. The price is pegged to the marginal kg, which is basically the world price. Propane pricing may be used as a proxy for LPG. Natural gas liquids, including propane, generally track the oil price. Short term volatility in the price of oil has become a way of life since about 2014. In the US, propane has been priced as low as USD 3.63 per million BTU in January 2016 and a scant two years prior to that was at USD 15. These fluctuations will be very hard on the poor in villages, even if respective governments act to ameliorate with subsidies. The practice of “stacking”, comprising switching back to wood, at least in part, will vitiate the gains.

LPG, undeniably carrying the label of a fossil fuel, may well be the means for improving air quality for the poorest and for addressing the single biggest public health problem in the world today. Labels can be deceiving.

Vikram Rao