Indoor Air Quality and Nitrogen Oxide Transport in Energy-Efficient Buildings: A Review

Abstract

Energy codes require envelope airtightness that pushes natural air exchange below 0.30–0.35 h−1, turning the dwelling into a partly closed compartment of the reactive nitrogen cycle. This review synthesizes 82 studies on reactive nitrogen (NO, NO2, HONO) in energy-efficient buildings. The novelty of this review consists of three elements. First, it organizes the evidence around a mass balance for reactive nitrogen rather than around building typologies. Second, it uses the Damköhler number as a single criterion for when indoor transport and chemistry must be solved together. Third, it derives, from published parameters, the ventilation rates a cooking event would require. Emission factors for unvented gas cooking converge on 29.3–42.5 ng NOx J−1 expressed as NO2-equivalent, of which primary NO2 accounts for 7.8–9.1 ng J−1, with NO exceeding NO2 by 1.8–2.7 times. NO penetrates the envelope unimpeded; NO2 penetration is 0.72 ± 0.06 with a humidity-dependent loss rate of 0.27 ± 0.12 h−1. Reactive nitrogen cannot be treated as a passive scalar in quiescent zones of airtight dwellings, where air speeds fall below about 0.03–0.06 m s−1 at 20–40 ppb indoor ozone, whereas the bulk of a mixed room remains in the passive-scalar regime. Using the primary NO2 emission factor, the mass balance shows that keeping the hourly mean below the 1 h guideline during a 30 min cooking event would require 2.9–18.4 h−1, one to two orders of magnitude beyond z ventilation. NO2 removal is governed jointly by ventilation and surface uptake, so carbon dioxide is an unsuitable surrogate for demand-controlled ventilation.