Indoor air pollution

WHO indoor air quality guidelines: household fuel combustion

Recommendation 1: Emission Rate Targets

Emission rates from household fuel combustion should not exceed the following targets (ERTs) for particles with aerodynamic diameters of less than 2.5 µm (PM2.5) and carbon monoxide (CO), based on the values for kitchen volume, air exchange and duration of device use per day set out in Table R1.1 and which are assumed to be representative of conditions in low- and middle-income countries:

PM2.5 (unvented): 0.23 (mg/min)
PM2.5 (vented): 0.80 (mg/min)
CO (vented): 0.16 (g/min)
CO (vented): 0.59 (g/min)

The vented ERTs assume an average value of 25% of total emissions entering the room.

Strength of recommendation: Strong

Purpose of recommendation: To answer the question: “What device- and fuel-emission rates are required to meet WHO (annual average) air quality guidelines and intermediate target-1 for PM2.5, and the (24-hour average) air quality guideline for CO?” Such emission rates can provide, with suitable testing, a basis for selecting appropriate devices and fuels.

Implementation guidance
a) Other pollutants: This recommendation focuses on two of the most important products of incomplete combustion, PM2.5 and CO; however, WHO recognizes the importance of other pollutants as well: e.g., toxic components of coal or emissions of nitrous oxide from gas appliances.
b) Multiple devices and guidelines: The use of multiple devices to meet total daily home energy needs is common. The emission rate targets in this recommendation apply to each individual device used for cooking, heating or lighting. If the sum of the duration of use per day across all devices in each home is not exceeded by that assumed by the model, the percentage of homes meeting the WHO air quality guidelines will be the same, assuming all devices meet the emission rate targets.
c) Modelling and simulation: For details of input variables and methods, please see Review 3 (Emissions model). Plans for increasing the applicability of the model to more specific regional settings, and providing a user interface to input locally-derived data, are described under Support for Implementation.
d) Opt for most stringent targets, where possible: Health-oriented programmes promoting fuel/device combinations should over time opt for the most stringent emissions targets and measures to optimize use of the healthier technology, and ensure the repair or replacement of non-compliant devices.
e) Outdoor devices should meet indoor standards:The emission rate targets apply primarily to indoor environments, but to maximize health benefits outdoor stoves, heaters and lamps should also meet the same fuel-combustion standards. A higher percentage of homes where outdoor or semi-outdoor cooking is prevalent would likely meet WHO’s air quality guidelines, than homes where cooking is done indoors. Studies show, however, that people cooking outdoors on traditional stoves are still exposed to high levels of pollution. Furthermore, emissions to the outdoor environment reduce community ambient air quality, which in turn contributes to lower indoor air quality.
f) Short-term CO emissions:The recommended emission rate targets (and intermediate targets) protect against longer-term impacts of CO, but are not intended to address short-term emissions limits protecting against the acute effects of CO poisoning
g) Monitor and evaluate:Recommendation 1 aims to provide guidance on predicted area concentrations of PM2.5 and CO in kitchens, based on emission rates from testing of the stove or other devices. Effective management of household air pollution, however, also requires that assessment of actual use and performance in homes is also done as part of a monitoring and evaluation strategy (see also Recommendation 2).

Indoor air quality guidelines: household fuel combustion
The full text of Recommendation 1: Emission rate targets, including remarks, summary of evidence and research recommendations are available in Section 4.3 of the guideline document.
Data Table R1.2: Emission rate targets (ERT) for meeting WHO air quality guidelines for PM2.5, including a less stringent intermediate ERT for which 60% homes would meet the guideline.
Data Table R1.3: Emission rate targets (ERT) for meeting WHO air quality guidelines for CO, including a less stringent intermediate ERT for which 60% homes would meet the guideline.