Are building and furnishing materials sources or sinks of indoor air pollutants?

Why is this important?

Building and furnishing materials take many shapes and forms (e.g. plasters, paints, carpets), and are ubiquitous in all buildings. We need to understand what impact they have on indoor air quality (IAQ) and whether we can identify some that have lower emissions to recommend for more general use. There is a whole market now around so-called ‘green materials’, but very little research has been carried out on whether the emissions from these are lower than from more traditional materials, how the composition varies between the different materials and how they impact IAQ. If such materials become more ubiquitous in our homes, it is important we understand what impact they are having on indoor air quality.

What do we already know?

We already know that there is a large variation between emissions from different materials, both in terms of magnitude and also composition. Even for the same materials, emissions can vary with age, temperature and humidity (e.g. Kruza et al., 2017). Emissions can be considered to be primary or secondary. Primary emissions are emitted directly from the material, and tend to be highest when the material is first made (e.g. new furniture smell) and then decline with age, whilst secondary emissions can occur when an oxidant such as ozone deposits on the surface, chemically interacts with a component of it, and leads to emissions of new species (e.g. Kruza et al., 2017). Unlike primary emissions, these secondary emissions tend to depend on other factors (e.g. oxidant concentrations and the composition of the surface) and can still be substantial even after some time has elapsed. Note that this secondary emission process removes one air pollutant (ozone), but emits others (carbonyls). The balance between these two processes will determine whether a specific material acts as an overall source of or sink for pollution indoors. However, at the moment, we lack the detailed measurements that can provide us with this information.

Composition and manufacture of building and furnishing materials is increasingly being driven mainly through consideration of sustainability and energy efficiency. These materials are intended to be environmentally friendly, and may have characteristics such as low toxicity, minimal chemical emissions, the ability to be recycled, and better durability. Emissions from such materials tend to be lower than their non-green alternatives as discussed in chapter 4 of our WG3 report. Some materials claim to go a stage further by removing pollutants from the air, such as catalytic paints, although some of them produce other pollutants whilst doing so (again, chapter 4 of WG3 report). However, at present, there have been relatively few studies that have compared traditional and green materials in terms of their overall impacts on IAQ, or indeed on identifying those which lead to optimal IAQ.

What to measure?

The species emitted from building materials are listed based on our work for WG3 here and comprise numerous VOCS from many different chemical classes. Formaldehyde is one of the most ubiquitous species, but there are also numerous aromatic species emitted. Green materials tend to emit mainly terpenes as described in this table from WG3. We also provide information on the species expected to be emitted from the use of photocatalytic materials, though there is much less information available.

How should we measure these species?

We suggest that pollutant deposition and reactive products generated on indoor surfaces (e.g. carpets and furniture), including zero/low emitting materials or materials that actively remove pollutants should be characterised for a range of typical indoor conditions. Although analysis of removable building materials can take place in the laboratory, it is also important to study them in situ where they can interact with their environment. Specifically:

Ozone : WG4 work described in Part 5.2.1, p13 in Sampling and analysis techniques for inorganic air pollutants in indoor air

VOCs: refer to Mapping organic constituents and WG4 Full article: An overview of methodologies for the determination of volatile organic compounds in indoor air

Where should we measure these species?

 Ideally, an as wide a range of buildings as possible. It would be beneficial to understand how IAQ differs between conventional and green dwellings and in different countries with different green certifications and different climates.