Helen C. Shields

Potential reactions among indoor pollutants

Abstract Reactions among indoor pollutants can produce products that, otherwise, might not be present in an indoor environment. To be relevant in an indoor setting, a chemical reaction must occur within a time interval shorter than or comparable to the residence time for a packet of indoor air. At typical air exchange rates, the reactions that meet this criterion include those of ozone with nitric oxide, nitrogen dioxide, and selected unsaturated hydrocarbons; thermal decomposition of peroxyacyl nitrates; numerous free radical reactions; and selected heterogeneous processes. Stable products include aldehydes, ketones, carboxylic acids and various organic nitrates. These reactions also generate free radicals, starting with the nitrate radical, Criegree biradicals, and peroxyacyl radicals, and leading to the hydroxyl, alkyl, alkylperoxy, hydroperoxy, and alkoxy radicals. Such radicals can react with other indoor species yielding additional aldehydes, ketones, carboxylic acids, dinitrates and peroxyacyl nitrates. Some of the potential products are known or suspected to be irritating (e.g. methacrolein, nonanoic acid, 1,2-propanediol dinitrate, peroxybenzoyl nitrate, and radical anions of the type [Cl… NO2]−) However, some of these same products are difficult to detect using the sampling and analysis techniques currently applied to indoor air.

Indoor Ozone Exposures

Indoor and outdoor ozone concentrations were measured from late May through October at three office buildings with very different ventilation rates. The indoor values closely tracked the outdoor values, and, depending on the ventilation rate, were 20 to 80 percent of those outdoors. The indoor/outdoor data are adequately described with a mass balance model. The model can also be coupled with reported air exchange rates to estimate indoor/outdoor ratios for other structures. The results from this and previous studies indicate that indoor concentrations are frequently a significant fraction of outdoor values. These observations, and the fact that most people spend greater than 90 percent of their time indoors, indicate that indoor ozone exposure (concentration X time) is greater than outdoor exposure for many people. Relatively inexpensive strategies exist to reduce indoor ozone levels, and these could be implemented to reduce the publics total ozone exposure.

Indoor Chemistry Involving O3, NO, and NO2 as Evidenced by 14 Months of Measurements at a Site in Southern California.

For more than 1 year, indoor and outdoor 0 3 , NO, NOz* (NO, NO), temperature, and relative humidity as well as the air exchange rate have been measured continuously at a commercial building in Burbank, CA. The indoor concentration of a given pollutant is a function of its outdoor level, the air exchange rate, the rate at which it is removed by indoor surfaces, and the rate at which it is produced or removed by indoor chemistry. Several examples of indoor chemistry are inferred from daily and seasonal variations in the collected data. These include homogeneous reactions such as those of 03 with both NO (fast) and NO2 (slow) and heterogeneous reactions such as those between NO2 and indoor surfaces. The latter ultimately contribute to indoor levels of both HONO and NO and are more likely to be observed in the absence of indoor 03. Indeed, due to the very rapid 0 3 / N 0 reaction as well as other slower reactions, the presence or absence of indoor O3 strongly influences speciation among the indoor oxides of nitrogen.

Analysis of Ambient Concentrations of Organic Vapors with a Passive Sampler

Volatile organic compounds can contribute to the failure of electronic equipment in both switching offices and data centers. They can also be useful indicators of ventilation needs. Only within the past decade have ambient concentrations of volatile organics been measured routinely. In standard sampling approach, a pump is used to pull a known volume of air through an adsorbent. This study examines a sampling procedure that does not use a pump, but instead depends on molecular diffusion for eventual contact between the vapor phase compounds and the charcoal sorbent (passive sampling). The technique is both simpler and less expensive than active sampling with a pump. This method has been validated for low-level sampling over extended time intervals. This study demonstrates that collected amounts vary linearly with airborne concentrations for sampling intervals in excess of four weeks: even after eight weeks of sampling at typical ambient concentrations, the amount of material collected does not approach th...

Volatile Organic Compounds Measured at a Telephone Switching Center From 5/30/85-12/6/88: A Detailed Case Study

Volatile organic compounds (VOCs) can cause failures in electronic equipment. This paper presents detailed observations from a three year study of VOCs at a telephone switching office in Neenah, Wisconsin. Included are data on matched indoor and outdoor VOC measurements, as well as corresponding data on HVAC fan operation and ventilation rates. The Neenah office has few occupants and hence provides an opportunity to examine factors that influence VOC levels without the complications associated with daily human activities. As reported in other studies, total VOC levels indoors were greater than those outdoors. During normal periods (no renovation or construction) the total VOC levels were inversely proportional to the air exchange rates. The sources with the greatest influence on the VOC levels tended to be those with the greatest surface area. The results demonstrate that low baseline levels of VOCs (total VOCs < 60 μg/m3) can be achieved by minimizing VOC sources and providing adequate ventilation. Even ...

Deposition of Airborne Sulfate, Nitrate, and Chloride Salts as It Relates to Corrosion of Electronics

The intent of this study was to determine if the range in surface accumulation rates of corrosive ionic substances at the Newark and Neenah locations is a result of variability in the corresponding airborne concentrations across the equipment room or other factors

The effects of ventilation, filtration, and outdoor air on the composition of indoor air at a telephone office building

Sensors installed at a telephone office building in Neenah, WI, continuously monitor 24 parameters related to the operation of the buildings heating, ventilating, and air conditioning (HVAC) system. This data is stored in a dedicated minicomputer and can be retrieved, in various formats, for subsequent analyses. For more than a year, we have measured indoor and outdoor concentrations of both fine and coarse airborne particles, their chemical constituents, and volatile organic compounds at this same location. Using this data, we have examined the composition of the indoor air as it correlates to the composition of the outdoor air and the various HVAC operating parameters. The steady-state indoor concentrations of the particles, particulate constituents, and organic vapors can be explained in the context of a mass balance model. This model can also be used to calculate the rate at which selected chemicals are generated within the building, as well as to predict resulting changes in steady-state indoor concentrations when changes in the ventilation or filtration parameters are made. Examples of each of these applications are given.