Abstract

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. Panels attached to buildings and hardscape, regularly desorbed, could offer public health co-benefits in an environmental justice context.