Indoor acids and bases

Abstract

Numerous acids and bases influence indoor air quality. The most abundant of these species are CO2 (acidic) and NH3 (basic), both emitted by building occupants. Other prominent inorganic acids are HNO3, HONO, SO2, H2SO4, HCl, and HOCl. Prominent organic acids include formic, acetic, and lactic; nicotine is a noteworthy organic base. Sources of N‐, S‐, and Cl‐containing acids can include ventilation from outdoors, indoor combustion, consumer product use, and chemical reactions. Organic acids are commonly more abundant indoors than outdoors, with indoor sources including occupants, wood, and cooking. Beyond NH3 and nicotine, other noteworthy bases include inorganic and organic amines. Acids and bases partition indoors among the gas‐phase, airborne particles, bulk water, and surfaces; relevant thermodynamic parameters governing the partitioning are the acid‐dissociation constant (Ka), Henry's law constant (KH), and the octanol‐air partition coefficient (Koa). Condensed‐phase water strongly influences the fate of indoor acids and bases and is also a medium for chemical interactions. Indoor surfaces can be large reservoirs of acids and bases. This extensive review of the state of knowledge establishes a foundation for future inquiry to better understand how acids and bases influence the suitability of indoor environments for occupants, cultural artifacts, and sensitive equipment.

Particulate matter emitted from ultrasonic humidifiers—Chemical composition and implication to indoor air

“…42,43 The only identified indoor source of sulfate is the use of kerosene stoves. 3 Our study demonstrates for the first time that the operation of ultrasonic humidifiers can serve as a significant source of SO A class of organic compounds of great relevance to tap water is disinfection byproducts (DBPs), which arise from chlorination of residual dissolved organic matter in water. Extensive research has been conducted for DBPs and their toxicity to humans.…”

“…59 The indoor air contains numerous acidic and basic chemical compounds, the partitioning of which is highly dependent on the pH of the condensed phases. 3 In particular, acidic compounds tend to undergo partitioning to basic condensed phases, as deprotonation of acids reduces their volatility. Thus, inhalation of humidifier-generated PM may represent a previously unrecognized exposure pathway for certain acidic compounds.…”

“…A number of comprehensive review articles and book chapters have been published recently on topics relevant to indoor air, including atmospheric chemistry, indoor PM, source of pollutants, exposure, and health effects. 3,4,[23][24][25][26][27] The word "humidifier" did not appear in any of these articles, except for Nazaroff and Weschler, who mentioned that humidifiers could be a source of amines. 3 The number, mass concentration, morphology, and size distribution of PM emitted from portable humidifiers have been investigated.…”

“…3,4,[23][24][25][26][27] The word "humidifier" did not appear in any of these articles, except for Nazaroff and Weschler, who mentioned that humidifiers could be a source of amines. 3 The number, mass concentration, morphology, and size distribution of PM emitted from portable humidifiers have been investigated. 13,[28][29][30][31] Chemical composition is determined by only a few studies.…”

Negative ions offset cardiorespiratory benefits of PM 2.5 reduction from residential use of negative ion air purifiers

“…The levels of personal exposures to different pollutants and NI were calculated based on the time‐activity patterns surveyed by questionnaire and real‐time indoor and outdoor concentrations of air pollutants as described previously 9 . Because indoor NO 2 , SO 2 , CO, and O 3 concentrations were not expected to be affected by NIAPs, based on the physical characteristics of the dormitories and reports in the literature, 9,20,21 we estimated their levels in the dormitory rooms assuming indoor/outdoor (I/O) ratios of 0.7, 0.4, 1.0, and 0.2 for NO 2 , SO 2 , CO, and O 3 , respectively. Because some participants have spent a small fraction of time in rooms without interventions (eg, classroom), we made another assumption based on our previous findings that the I/O ratios of PM 2.5 in an unknown indoor environment were 0.9 when windows were open and 0.7 when windows were closed 9 .…”