The reactive nitrogen species, nitrous acid (HONO), ammonia (NH3), and amines (NR3) are critical to chemistry of the outdoor environment. These species are also expected to impact indoor chemistry. To understand this chemistry, accurate quantitative measurements of HONO, NH3, and NR3 that are suitable for routine application to indoor environments are necessary.
In the outdoor environment, HONO is an important radical source. It is readily photodegraded (λ ≤ 400 nm) to form the hydroxyl radical, which initiates oxidation reactions and secondary organic aerosol formation. The photolability of HONO makes it an important radical source in low-light conditions, such as early morning, and means it may act as an indoor radical source. Reaction of HONO with NR3 leads to the formation of nitrosamines. Although these NR3 reactions are unimportant outdoors, they may play an important role in indoor chemistry. Indoors HONO has been found as a directly emitted species from gas stoves and other combustion processes. Formation of HONO by secondary processes has also been suggested, but the dominant formation mechanism is not yet clear and may change in the future with changing commercial product use.
Ammonia and NR3 are potent aerosol nucleators in the outdoor environment. They may similarly affect particle formation and growth indoors and alter the chemical nature of surfaces. Indoors, much of our knowledge concerning NR3 is related to emissions from cigarette combustion. With a decline in cigarette smoking indoors, other NR3 and their sources will be of increasing importance. Many known sources of NH3 and NR3 outdoors are likely to be present indoors, in addition to the widespread use of basic solutions as household cleaners, which may result in persistent release of these species indoors.
Ammonia, NR3, and HONO are part of the total reactive nitrogen (Nr) pool in the indoor environment. As described, these species are likely to impact chemistry indoors. However, there may be other species in the Nr category that may also play important roles in indoor chemistry. Our research will develop a total Nr instrument to set a quantitative bar on our closure of the emission, transformation, and fate of the entire Nr pool in the indoor environment, including HONO, NH3, and NR3. This platform will help detect and identify the chemical nature of previously unidentified nitrogenous species in the total indoor Nr budget
Current instruments for the measurement of HONO, NH3, NR3, and total Nr outdoors focus on the challenges unique to outdoor measurements and are not suitable for routine application indoors. Indoor measurement techniques for these species must be suitable for use: (i) in occupied indoor spaces; (ii) by non-experts; and (iii) in surveys of heterogeneous indoor environments. Explicit design of new methods that target the specific challenges and needs of the indoor chemistry community are therefore necessary. Our work will improve understanding of chemistry in the indoor environment by tackling the following three research questions:
- Can NH3 and NR3 be collected quantitatively in indoor environments by passive sampling?
- Can an interference-free passive sampling method for HONO be developed?
- Can the total Nr in indoor environments be quantified and fractionated with a simple and affordable real-time analytical platform?
Future updates can be found at: www.tcvandenboer.ca/indoorchem