LPG: Cooking and Health

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Selling LPG in Rwanda

LPG (liquefied petroleum gas) is among the most important fuels for achieving clean cooking. Many countries are actively developing intervention programs. In a five year project starting in 2007, an Indonesian program converted over 50 million households cooking with kerosene to LPG. In 2016, India intensified their campaign providing free connections to LPG cylinders to “Below Poverty Line” homes. In China, gas and biomass fuels, the dominant energy fuels for cooking, are used by 44.8% and 32.1% of households, respectively. In 2014, 47.6% of rural cooks used biomass, whereas urban households were more likely to cook with gas (65.8%) (Applied Energy 2014, 136:692-703 Duan, et al.).

Even older LPG stoves burn cleanly. Five different LPG stoves were tested 89 times and described in a 2018 article. Two stoves were manufactured in China and obtained in a local market near Beijing. One was manufactured in Japan and purchased in Kampala, Uganda. Solgas Repsol Downstream Peru (an international LPG distributor) disseminated another stove. A worn-out appliance was obtained from a rural household in Cameroon  (Environ. Sci. Technol. 2018, 52, 904−915 Guofeng Shen, et al.).

  • The average thermal efficiency for the LPG cook stoves was 51 ± 6%.
  • Approximately 90% of the PM2.5 data was below the level of detection.
  • The other 10% of the stoves had an average PM2.5 score of 0.20 ± 0.16 mg/minute. (The WHO Emission Rate target is 0.23mg/minute).

However, in a country like Rwanda the switch from wood and charcoal to LPG is slow. In 2019, only 2% of cooks were using LPG in the cities. 64% used a charcoal or wood stove and in rural areas “the use of clean fuels is negligible” (The World Bank, 2019). 93% of rural households use wood, 6% of charcoal, and 0.2% of gas (National Institute of Statistics Rwanda, 2019).

The cost of LPG is a big factor. “Prices are much higher in rural areas and upcountry towns as retail traders factor in transport logistics. Rising prices for cooking gas in the country have sparked concerns of likely reversing gains made in the push for a clean cooking solution as more households turn to wood and charcoal.”  

Marie-Jeanne Uwanyiringira, a businesswoman who sells LPG, says that the fluctuation in prices has caused frustration among consumers. “When someone buys gas from me at RWF 3,500 and the next month I tell them that it is RWF 5,500, ($5 USD) they don’t seem to understand that it is not the seller’s fault.” (Rwanda Today, April 9, 2021).

International Support for Cook Stoves and Climate!

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WASHINGTON, DC, April 22, 2021 — At the Leaders Summit on Climate hosted by President Biden, the U.S. government pledged to help countries achieve their climate ambitions through expanding access to clean cooking.

“Providing clean energy to households is critical to achieving global climate and sustainable development goals,” said Helena Molin Valdés, Head of the Climate and Clean Air Coalition Secretariat. “Smoke from fireplaces, cook stoves, and lighting is responsible for more than half of human-made black carbon emissions and millions of premature deaths from household air pollution. The Climate and Clean Air Coalition partners welcome the U.S. government’s re-engagement in the issue and look forward to cooperating to put in place solutions that improve lives and protect the planet.” 

The United Nations Foundation’s Clean Cooking Alliance

Would it be helpful to add climate metrics to the health-based ISO 19867? Currently, Scoring Tier 5 for emissions of PM2.5 and CO means that safety is assured in average households. As the score decreases from Tier 5 to Tier 0 the estimated amounts of ill health from breathing smoke and gas increase.

During ISO 19867 testing under an emissions hood, the fuel use, thermal efficiency and emissions of CO2, CO, and PM2.5 are measured and the data is used to determine a ranking on the voluntary tiers of performance. ARC multiplies lab data by a factor of three to estimate in field emissions. Usually in cook stoves, the CO2 has by far the largest effect on climate change. However, PM (black to white in color), CO, methane (CH4), non-methane hydrocarbons (NMHC), and nitrous oxide (N2O) also have varying amounts of climate forcing potentials. Currently, CO2, PM2.5, and CO are measured as a part of ISO 19867. ARC also determines the amount of black carbon in every test (using a filter) of PM2.5. Adding methane and non-methane hydrocarbons to the measured gases is not difficult. In fact, Sam is working on adding them to the LEMS right now.

The effects of inhaling particulate matter have been widely studied in humans and animals. They include asthma, cardiovascular disease, and premature death. Particles can also have an extremely strong effect on the atmosphere by absorbing and/or scattering the sun’s incoming radiation, depending on their color. The black particles have an approximate warming potential by weight of 680 times that of CO2 (Roden and Bond, 2006; Bond and Sun, 2005).

Total global warming impact, grams CO2 equivalent on a 100-year time-frame, per liter of water boiled and simmered for 30 minutes, normalized for starting temperature and fuel moisture content. Inclusive of CO2 and all PICs.

When we studied the global warming impact of five cook stoves burning biomass, CO2 was shown to be the major component, as seen above. At the time (2008), estimates of the various warming potentials were:

CO2….1  (IPCC, 2007)
CO….1.9  (IPCC, 2007)
CH4….25  (IPCC, 2007)
NMHC….12  (Edwards and Smith, 2002)
N2O….298  (IPCC, 2007)
PM – Black….680  (Roden and Bond, 2006; Bond and Sun, 2005)
PM – White….-50 (Estimate – Bond, 2007)

Warming potential, 100-year, CO2 equivalents

  • When biomass is harvested sustainably, the CO2 emissions from biomass-burning are considered to be greenhouse-neutral.
  • Although N2O is a strong climate-forcing constituent, emissions from the wood- and charcoal-burning stoves were very low, contributing less than 1% to the overall warming potentials.
  • The data suggests that there are biomass stoves that can be designed to (1) reduce the fuel used to cook, (2) reduce health-damaging emissions and (3) address climate change. The considerable differences in climate-changing emissions from the stoves in this study should be noted. Large-scale use of cleaner burning stoves might well reduce global warming effects, especially when the biomass is harvested in a “carbon neutral” manner. (N. MacCarty, D. Ogle, D. Still, T. Bond, C. Roden, Energy for Sustainable Development, 2008)

How Do We Know?

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When I went to UC Berkeley, studying psychology as an undergrad, lots of people made fun of Freud, Jung, and Adler who wrote (a lot) about divergent theories of what makes people tick. UCB liked to think of itself as a scientific institution, and facts are proven by statistical validity. Why should we believe speculation from the dear departed? I eventually agreed and I was intrigued by the big question: How do we know the truth?

The paradigm that captured my thinking was the BLACK BOX. In black box theory facts are like an elephant in a box. Scientists poke sticks into small holes in the box and one stick hits a toenail. A scientist exclaims, “Why, what is in the box is hard and slippery!” Other sticks hit the softer belly or the trunk, resulting in very different observations. Hopefully, after many experiments an accurate description of the elephant can emerge. (Although, what the elephant is thinking may well remain private.)

I was really excited by statistics!

If you’re trying to know the effectiveness of something, calculating the statistical significance can help. It gives you a measured amount of confidence in the hypothetical conclusion. At UCB we did experiments and 95% confidence was the minimum that students had to achieve to get an “A.” To achieve 95%, the sample size and the size of the effect had to be big enough.

Here’s the application to stoves: 

When we try to use found wood sticks from the forest in our experiments, one stick, for example, has two inches of bark on it. Another stick has three inches of bark and the two sticks make very different amounts of smoke. So, the variable of using sticks that emit different amounts of smoke makes it more difficult to know the truth: Did changing the air/fuel ratio, for example, result in the stove making less smoke? Using wood with no bark, we can achieve confidence in five to seven tests. We have to do a lot more tests when the fuel has added variables.

When trying to understand heat transfer or combustion efficiency in the lab (not what happens in the field) limiting variables has a great appeal to lazy researchers like me at ARC. So, we do not design stoves in the lab!

We realized quite a long time ago that we could only investigate heat transfer and combustion efficiency in the lab, and then with great relief go to an amazing place, work with wonderful people in a new culture, eat incredible meals, etc. in order to help a local team evolve a stove using found everything (and testing/statistics).