Efficiency and harmfulness of air-purifying photocatalytic commercial devices: From standardized chamber tests to nanoparticles release

• French and soon European standard for commercial photocatalytic air purifiers.
• Closed-chamber tests for air-purifier devices including a photocatalytic function.
• Determination of the clean air delivery rate and of the extent of mineralization.
• Two classes of commercial photocatalytic air-purifiers.

The aim of this study was the comparison of the efficiency of several commercial photocatalytic air-purifiers according to the French XP B44-013 AFNOR standard test (soon European) in a large closed chamber at the ppbV level under controlled conditions representative of indoor air. After inter-lab comparisons validating the method and analytical procedures, the commercial devices were evaluated for the mineralization of a mixture of four representative VOCs (acetaldehyde, acetone, n-heptane and toluene). Comparison of the degradation rate allowed the determination of the clean air delivery rate (CADR), while the mineralization efficiency was determined from CO2 analysis. The devices could be ranked in two classes: class 1 for efficient devices (high CADR, extended mineralization, no by-product) and class 2 for inefficient and unsafe ones (by-product release even in the absence of VOCs, low CADR and mineralization). Electrical low pressure impactor (ELPI) could not evidence any nanoparticles release with any of the studied devices. Formaldehyde was the main by-product detected in all cases, but the concentration remained low and decreased with time due to its total mineralization with class 1 devices. For class 2 devices, formaldehyde concentration was higher and went on increasing with time.These experimental data point out the urgent need of careful evaluation and certification of commercial photocatalytic air-purifiers for consumer's safety and secure development of the technology.

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