Introduction The severity of public health concerns brought about by air pollution is not in question. The Green Building Movement, emphasizing water and energy efficiency, use of recycled building materials, and lower-VOC, PM 2.5 and CO2 emissions in construction and daily operation, is an extraordinary advance in assuaging environmental concerns. This essay suggests a means to augment the ingenuity of these practices, mitigating ambient VOC air pollution by using shallow containers of adsorbent activated carbon, directly attached to structures, and regularly desorbed and replaced. This prospective measure offers a role to building exteriors, facing the often polluted ambient environment rather than the interior of the building envelope. This paper addresses green buildings in brief, and suggests how open panel adsorption could complement current measures. 1. Air Pollutants as a Public Health Concern The severity of the public Health Crisis of Criteria Air Pollutants and Volatile Organic Compounds is not in question. Air pollutants, specifically “criteria pollutants” designated as harmful to human health by the EPA, have been implicated in adverse respiratory, cardiovascular, and neuro-developmental outcomes. A surfeit of studies attests to this[1]. The problem is global, and relatively underfunded[2]. Greenhouse gases such as CO2 and CH4 are indeed an immense threat to global climate, but their mitigation does not obviate the need to ameliorate local criteria pollutant emissions and Toxic Air Contaminants. EPA National Ambient Air Quality Standards pollutants, comprising carbon monoxide, ozone, particulate matter, lead, nitrogen dioxide, and sulfur dioxide, remain a persistent threat in urban environments. The Persistent Problem of Volatile Organic Compounds Once one starts to unravel the list of aerosol pollutants, differences in treatment of different ones become clear. But VOCs are ignored, relatively speaking, especially in the United States. The dangers of VOCs, a number of which are designated TACs, or Toxic Air Contaminants for which there is no safe threshold level of exposure, are not unknown[3],[4]. TACs are tracked by the California EPA's Office of Environmental Health Hazard Assessment (OEHHA), by the CDC’s Agency for Toxic Substances and Disease Registry, and by the European Union and the World Health Organization. The risk of cancer and associated health effects have decreased, but geographically focused studies, such as the South Coast Air Quality Management District's longitudinal MATES, or Multiple Air Toxics Exposure Studies, have indicated that despite reduced cancer on the basis of gross population, local illness clusters persist[5]. They are thus well-understood in environmental health, and yet much of their regulation is overseen at the state and local level. Yet for the purposes of enforcement rather than public health study VOCs are, generally, not taken as seriously as they should be. VOCs are an increasing threat in a world with secular trend of higher temperatures. As ozone precursors, VOCs contribute to its production as a secondary aerosol product. Toxic Air Contaminants are prevalent in minor stationary facilities including point sources such as dry cleaners, auto body shops, junkyards, parking structures, gas stations, restaurants, the vicinity of construction dust, roofing work, diesel trucks and old cars, and other locations with ongoing, and widely tolerated fugitive emissions from building construction and repair. Such locations are neither major stationary polluters, nor major mobile source polluters, but are still practically speaking, miniature pollution hotspots. Enforcement penalties are almost invariably a day late and a dollar short. The usage of less-than-ideal fuels and combustion technologies as kerosene, propane, burning of firewood, other substances, cook-stoves, and cars in poor repair is clearly driven (so to speak) by necessity. While the why of remediation is beyond question, the how of the matter is a matter of engineering and instrumentation. We believe this is where green buildings could be even greener. 2. The Green Building Movement’s Air Quality Measures Green building design is a comprehensive approach to building materials and construction processes, and with indoor air quality and materials for the building occupants. LEED standards certification requirements, comprehensive and multi-faceted, emphasize water and energy efficiency, mandate use of recycled building materials, and require lower-VOC, PM 2.5 and CO2 emissions in construction and daily operation. For IAQ and for CO2 and VOC emissions from buildings, these are formidable requirements. Thorough and meticulous specifications are provided, regarding adhesives, sealants, and architectural coatings. (For the purposes of this essay we conflate LEED platinum certification and CalGreen Tier 2 or 2019 Title 24)[6]. CalGreen’s Title 24 is strengthened even further by the California 01350 Specification, which requires exposure chamber testing. San Francisco’s Rule 38, which mandates enhanced HVAC measures for all new buildings in areas with high ambient pollution, likewise improves IAQ. CO2 carbon neutral building materials also draw great attention[7]. Further innovative design approaches include integration of buildings into the earth, and agriculture and hydroponics integrated into building design[8]. Building materials and indoor furnishings that do not off-gas formaldehyde, and the like could drastically reduce sick building syndrome.3. Integrating Green Buildings into the Surrounding Environment This arsenal of measures represents immense progress. But green buildings are not primarily about the exterior of the building insofar as the ambient air is concerned. What they do not do is remedy ambient air in the built environment- except for prospective ambient pollutants coming from the building itself. VOCs and GHG emissions from the building itself are indeed brought to a fraction of their worst possibilities, yet the fact remains that the exterior environment often presents a noxious mixing ratio. At the same time, the filtration associated with LEED standards and the security measures associated with smart buildings enforces the impression that the modern smart building is a fortress from a dangerous world. The world is indeed dangerous- environmentally speaking and otherwise. It is this opposite side of the building envelope with which we are concerned. The most prominent buildings, displaying a LEED certification, do not exculpate themselves from the air pollutants which linger immediately outside and reappear as unwelcome guests on a daily basis. Open panel adsorption could alleviate these currently ignored ambient pollutants. Currently being tested, this process uses small screened panels of commodity granulated activated carbon are placed in polluted locations in order to adsorb VOC aerosols. After pollutants are adsorbed, the panels are desorbed, the contaminants incinerated or decomposed electrochemically, and the material is reactivated [9]. 4. Ambient Adsorption as Complement to Extant Practices Adsorption (physiosorption), in which process gases are taken in but not chemically combined with the substrate they interact with, is canonical in chemical engineering. AC is typically derived from processed coal, coconut coir or increasingly agricultural waste products (such as husks and fruit seeds). Spent carbon desorption and reactivation is carried out at regulated facilities, by thermal oxidation and thermal desorption in rotary kilns, destroying the VOCs and gases by pyrolysis. Alternative Regeneration methods for adsorbed AC, such as electrochemical treatment or microwave desorption are under development, most notably in Brazil and China.* Adsorption systems use closed reactor beds and a closely controlled and specified cubic feet per minute inlet to hasten the transfer of the molecules of the contaminant gases being adsorbed to the point at which the adsorbent material is saturated. Most uses are in industrial settings, and in Superfund and Environmental Remediation sites, rather than in open or ambient air. Yet far too much of the world looks like a Superfund site, and far too little VOC (and NAAQS pollutant) remediation is taking place. Current usage only addresses the problem at the most acute instances, in the case of permitted facilities, or at the source in the case of point sources such as dry cleaners. The empirical reality of AQ incidents is in most cases intermittent episodes of high pollution, often acute, but of short duration. Since VOCs are often averaged over a 24-hour period rather than time series like NAAQS pollutants, countless instances are being missed. Design for wider implementation is needed. Granulated AC can adsorb a great variety of air pollutants, and is even used in EPA's new 2012 method 325B for fenceline testing for benzene and related BTEX pollutants. But conditions which will facilitate this process in ambient air have not been established. Designing a simple adsorption system for ambient air is faced with the issue of diffusion in the low partial pressure of pollutants in ambient air. Micromitigation, or open panel adsorption, uses shallow lightweight panels of activated carbon attached to buildings and hardscape, and regularly removed and replaced from those surfaces, to remove ambient VOC pollutants. The MMWG is testing three strategies to adsorb effectively and economically in ambient air, with its characteristic lower VOC concentrations and air pressure (relatively to industrial settings). The first is repeated flows to the adsorbent material, achieving saturation over a much longer duration. The second strategy is deployment locations carefully chosen in order to maximize persistent and episodic acute air pollutant concentrations. Finally, the method increases the adsorbent surface area even further by designing panels open to the air. Screened mesh coconut shell AC are placed in strategically chosen locations where pollutants are especially dense, or where air flow is laminar with low friction (because of impermeable adjacent vertical walls for instance) to facilitate adsorption. This design thus alternately utilizes the relatively passive diffusion of batch adsorption systems, and effusion under pressure used by the more prevalent tubular or plug flow or column reactor adsorption system[10]. Initial experimental results have been encouraging[11]. Preliminary desorption reports indicate that passive ambient adsorption over a period of time works[12]. Issues and Concerns in Implementing Ambient VOC Mitigation The first of several immediately obvious issues is the blackbody problem, that is, the thermal effects of carbon AC in sunlight, taking in radiant energy and evolving heat. In contrast, much current building design is to deflect light, using surface and color high albedo to reflect light rather than absorb light and heat. This is much in evidence in the Cool Cities approach and derived cool pavements projects and practices. It appears that exterior walls of new, prominent and high-end environmentally certified buildings serve this cooling function. Open panel adsorption is not intended to create or contribute to heat islands, and adsorption itself does not work as well at higher temperatures. Alleviating the prospective heat evolved by open panel adsorption should not be an insurmountable challenge. Adsorption panels could incorporate light-colored PM 2.5 baffles to both deflect heat adsorption and to bin particulates before they reach the panels. Such panels could be part of a non-load bearing curtain wall. This could represent a modification of current design of external walls in environmentally friendly buildings. Such walls are, in most cases, impervious and not apparently designed with alleviation of ambient pollutants. This is true of San Francisco’s Millennium Tower and Salesforce Tower, as well as CARB’s new HQ in Riverside and the Apple HQ in Cupertino, all of which have impervious walls. An interesting possibility is building construction which would facilitate the placement and removal of adsorption panels. Slotted brackets added to the sides of buildings, at a height of ten to fifteen feet, co facilitate routine placement and replacement of open adsorption panels. Moreover, the design of such brackets could allow space between the building and the adsorption panel itself, again reducing the prospect of overheating by the panels. Such placement and routine removal and replacement of panels could be built into building design and maintenance. The sides of buildings, especially in high-rises and dense residential neighborhoods adjacent to traffic, are perhaps the most likely large-scale usage. 5. Implications for the Built Environment Widely implemented, OPA could be consequential for public health, building design, and community development. Applications in ambient air improvement would take considerable time to be quantified through epidemiological studies. Reduced TACs could mean tangible, material improvement in health in both sensitive receptors and everyone else. Modify Building Design Perhaps most interesting from a visual perspective is what it could do to alter building appearance. As mentioned, the current aesthetic leans toward the sleek and the aerodynamic. Adsorption modification measures could provide a look that is more earth-toned, and granular looking. The widespread implementation of adsorption tech adhering to building sides could mean that buildings could take on an unanticipated role in urban planning and pollution remediation outside the building envelope itself. Hardscape: The Contributions of Humble Buildings OPA could give increased functionality to hardscape and to a variety of utility structures. Frequently associated with transportation, such edifices as bus stops, entrances and safety guards for light rail lines, surfaces of arterial roadside barriers, utility buildings; on-ramps and off-ramps in cities and towns, all have surfaces on which OPA could be implemented. It's no surprise that such structures are typically besieged by air pollution, given their typical proximity to major sources of NAAQS and VOC emissions[13]. Other amenable structures are not buildings strictly speaking but include utility and navigational signage; street signage, utility fencing, safety and traffic diversion structures adjacent to construction work. This could also include the gamut of hardscape- staircases, landscaping, curbs adjacent to driveways, walls adjacent to parking structures. The functionality of structures could be transformed beyond the purpose for which they have been constructed. Air Quality as a central concern of public spaces The increased attention that MM could bring to air quality issues in otherwise ignored public spaces, could be a boon to the unhoused, informal economy participants who work at open markets or on sidewalks or plazas, and basically to everyone who lives and works in deep urban canyons. Ostensibly obscure public spaces, often in business or light industrial areas, are actually ones in which people spend a great deal of time. Likewise, open panel adsorption could draw greater attention to urban structures, aspects of the built environment that are also putatively obscure. We want this to take concrete [sic] form by improvement of quotidian, pedestrian public spaces. In addition to air quality mitigation itself, it could bring about concurrent changes to community life. It could lend even more urgency lent to environmental justice issues in non-attainment neighborhoods. We would also hope for a new and fruitful association between local communities and university and scientific communities. Indoor Air Quality Increased attention to indoor air quality is one of the paltry few positive and constructive advances to have come out of the ongoing horror of the Covid-19 pandemic. This includes new products at all price levels; from modest Smart Air filters and economical self-assembled Corsi-Rosenthal boxes[14] to the luxurious Molekule and Dyson product lines. There is much room for attention to IAQ beyond this[15]. Open Panel adsorption could draw more attention to the usage of VOCs in household products (cleaning sprays, dryer sheets, laundry detergent, scented candles, air fresheners). This is in itself a public health problem, although one only addressed indirectly here but of increased concern in academic circles[16]. 6. Conclusion As the human cost of aerosol pollutants is at long last taken seriously, we anticipate that the cost of VOC emissions mitigation will increasingly seem less and less expensive. Remediating the excesses of the industrial 20th century is a momentous and daunting challenge that will demand the energy and ingenuity of the 21st century. This method could contribute to that task. The prospects of open panel adsorption are especially exciting when we consider the sheer expanse of surface occupied by building exterior walls. Integrating building design with improvements to ambient air quality could augment current green building design. Such measures could brighten the countenance of prominent urban buildings as well as the face of the subaltern, obscure locations of cities- to borrow the evocative words of U2- the places "where the streets have no names". [1] WHO docs, ALA 2020 State of the Air; IPCC 2018.[2] NAAQS; WHO, EU.[3] World Health Organization. WHO Guidelines for Indoor Air Quality: selected pollutants. WHO: Copenhagen, Denmark. 2010.[4] Galezowmska, G., M. Chraniuk, I. Wolska." In vitro assays as a tool for determination of VOCs' toxic effect on respiratory system: a critical review". Trac-Trend Anal. Chem. 77 (2016) 14-22.[5] Propper et al. 2015, p11335.[6] Other green standards and credentials include LBC Petal; Well v2 Pilot, LEED Platinum and the ILFI net zero carbon, as well as building codes in specific cities.[7] Brent Constantz, founder of Blue Planet, which makes CO2-rich and thus carbon-negative concrete, has found himself a celebrity in Green circles in recent years. During a talk he gave in 2018, he paused and surveyed the packed audience of municipal civil engineers in a crowded San Francisco city agency office, and said" "People didn't used to be this interested in concrete!"[8] Doug Jackson, ed. Super Green! Souped up Green Architecture. New York: Actar Publishers 2017. Wines, James. Green Architecture. New York: Taschen. 2000.[9] This citizen science initiative seeks to establish an open-source protocol to abate VOC air pollution, and disseminate it by CERN Open Hardware License (Permissive, 2020 v2), or a similar license. The Micromitigation Working Group, a bi-monthly Meetup hosted since April 2021 by the open science Counter Culture Labs in Oakland, California, is developing this method.[10] Testing, OPA design, and instrumentation are addressed in the proposal, https://github.com/rebeccaelizskinner/Open-Panel-Adsorption10PageJune2023 . [11] The first test was deployed in ambient air near a six-lane arterial street at the intersection of Alemany Boulevard and Habitat Terrace in San Francisco. The sample of the adsorbed AC was tested at an analytical laboratory by GC-MS analysis through thermal desorption (TD GC-MS), using a modified EPA Method TO-17 protocol. The results indicated significant hydrocarbons, including chlorinated and aromatic rings species. Despite concerns, the AC was not blinded by PM 2.5 nor did competition from adsorbed H20 preclude adsorption of VOCs.[12] To determine how rapidly breakthrough occurs, we are carrying out timed tests of AC sorbent material in glass jar, with VOC-saturated air, with a Photo-Ionization Detector. [13] Samal, Choudhury, et. al." Air pollution in micro-environments: a case study of India habitat center". Indoor and Built Environment. August 2013. 22,4: 710-718. Hicklin, William et.al." Investigation of VOCs in and around buildings close to service stations". Atmospheric Environment January 2018. 172,1: 93-101. [14] https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box.[15] Jiang, Zhuoying and Xiong Yu."Kinetic studies on using photocatalytic coatings for removal of indoor V O Cs." Indoor and Built Environment. June 2020. 29, 5: 689-700.[16] Anna L. Hodshire et. Al. “Detailed Investigation of the Contribution of Gas-Phase Air Contaminants to Exposure Risk during Indoor Activities. Environ. Sci. Technol. 2022. 56, 12148-12157.
