The threat to human health posed by Volatile Organic Compounds- carcinogenic substances for which the EPA has set no safe threshold exposure levels- is profound^[1]. Despite international^[2], national and state air quality standards, and greatly improved air quality monitoring, exposure remains a health hazard. 

   Open panel adsorption, an open-source technical solution to mitigate ambient VOCs, uses small screened panels of commodity granulated activated carbon placed in locations polluted with VOC aerosols. After pollutants are adsorbed, the panels are desorbed by pyrolysis or thermal oxidation and contaminants incinerated, and the material is reactivated. Alternative methods such as electrochemical treatment or microwave desorption are under development.    A simple adsorption system for ambient air is faced with atmospheric humidity, the erratic mixing ratio of ambient air, and diffusion in the low partial pressure of pollutants in ambient air. Adsorption systems use closed reactor beds and a closely controlled and specified cubic feet per minute inlet to hasten mass transfer to breakthrough (saturation and dynamic equilibrium).     OPA relies on 1) repeated flows to the adsorbent material, achieving saturation over a much longer duration; 2) deployment locations carefully chosen in order to maximize persistent and episodic acute air pollutant concentrations; and 3) increasing the adsorbent surface area by designing panels open to the air.  Adsorption panels should be placed in locations where pollutants are dense, preferably 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.

   Timed jar tests utilize AC sorbent material in VOC-saturated air, with a handheld Ion Science Cub Photo-Ionization Detector unit placed into a 2.3 cubic Liter Rubbermaid Brilliance container. These tests have indicated favorable adsorption with repeated introductions of TVOC (nail polish remover), as well as rapid adsorbance under varying light, RH, and air turbulence conditions. Another initial experiment used screened panels of 4x8 mesh coconut-shell AC, adjacent to a six-lane arterial urban route. Tested by TD-GC-MS analysis using a modified EPA Method TO-17 protocol, the panels evidenced significant hydrocarbon species. Crucially, the AC was not blinded by PM 2.5, nor did competition from adsorbed H20 hinder adsorption of VOCs.    We calculated cost for the first TVOC removal test (See Attachment A, 11.30.2022, and Appendix 3).  The rate equation of 1969.8 ppm removed over 135 minutes is 14.5911, that is 14.5911 ppm removed per minute.  Alternatively, one could say that the 50 grams of AC with a delta of 1969.8 ppm, removes 39.396 ppm of TVOC per gram of Activated Carbon, over two and one-quarter hours.  Since GAC cost $22.99 for five pounds, the 50 grams of AC, at 0.11.231 lb., cost 50 cents (0.506842). At one penny per gram, or about 40 cents to remove 39.393ppm TVOC, this is modest in price. This would be more emphatically the case with the most rapid rate equations- those for the first round of adsorption, in sunlight, from the maximum reading to 5.0ppm. In such cases, with a higher rate equation of per-minute adsorption, the cost would be less than one gram, or one penny, per minute as 14.5911ppm TVOC is removed. The cost per-ppm adsorbance metric is significant for the case for OPA, which is intended for circumstances in which and constituencies for whom time is less dear than money. The cost of the complementary processes of desorption and decomposition, by any one of several methods, is being explored.

     These preliminary findings affirm the working hypothesis: ambient diffusion will do the job of adsorption, and a columnar reactor with no PSA or TSA mechanism exerted. Ambient adsorption using only diffusion may not complete its work optimally, but well enough for the circumstances for which OPA is intended. Panels attached to buildings and hardscape, regularly desorbed, could offer public health co-benefits in an environmental justice context.

^[1] Propper, Ralph¹ [email protected] Wong, Patrick et al. “Ambient and Emission Trends of Toxic Air Contaminants in California. Environmental Science & Technology. 10/6/2015, Vol. 49 Issue 19, p11329-11339.

^[2] Air quality guidelines for Europe: second edition. WHO Regional publications. European series No 91.