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The Transformation of Outdoor Ammonium Nitrate Aerosols in the Indoor Environment
| Content Provider | Semantic Scholar |
|---|---|
| Author | Lunden, Melissa Littlejohn, David Fischer, Marc L. Hering |
| Copyright Year | 2005 |
| Abstract | Recent studies associate particulate air pollution with adverse health effects; however, the exposure to indoor particles of outdoor origin is not well characterized, particularly for individual chemical species. In response to this, a field study in an unoccupied, single-story residence in Clovis, California has been conducted. Real-time particle monitors were used both outdoors and indoors to quantify PM2.5 nitrate, sulfate, and carbon. The results show that reduced indoor sulfate and carbon levels are primarily due to deposition and penetration losses. However, measured indoor ammonium nitrate levels were often observed to be at significantly lower levels than expected based solely on penetration and deposition losses. The additional reduction appears to be due to the transformation of ammonium nitrate into ammonia and nitric acid indoors, which are subsequently lost by deposition and sorption to indoor surfaces. The size of the effect is dependent upon factors such as temperature, relative humidity, and ventilation rate. INDEX TERMS Aerosols, penetration, chemical transformation, ammonium nitrate, nitric acid, ammonia INTRODUCTION An understanding of the underlying reasons for the causes of the adverse health effects resulting from ambient particulate matter (PM) is of major scientific importance. These adverse health correlations are based upon data from outdoor regional monitoring sites (Dockery, et al., 1993, Pope, et al., 1995). However, individuals spend, on average, about 90% of their time indoors 70% of that in homes (Jenkins, et al., 1992). This implies that indoor exposure to PM2.5 of outdoor origin may be an important element in determining the causes of these health effects. To investigate the dynamics of indoor particles of outdoor origin, we performed a controlled series of intensive field experiments on an unoccupied, single-story residence in Clovis, California, a suburb of Fresno, in California's San Joaquin Valley. The conditions in the residence were manipulated to cover a wide range of conditions during several weeks of intensive measurements periods. The measurements focused on providing data on indoor and outdoor concentrations of PM2.5 particles as a function of chemical concentration under a variety of house ventilation, heating and cooling conditions. Indoor sources were minimized to enhance understanding the mechanism of the transport of outdoor particles indoors. * Contact author email: MMLunden@lbl.gov 2 METHODS The experimental facility is a three-bedroom, single-story home (134 m) constructed in 1972. The house has standard height ceilings (2.4 m), a forced air heating and cooling system, and ceiling fans. The house is located in a residential suburb, surrounded by homes of similar size and mature trees. The flat topography of the area combined with the mature vegetative growth near the home resulted in low levels of wind loading around the building. The chemical concentrations of indoor and outdoor aerosols were measured simultaneously with 10-minute time resolution using the integrated collection and vaporization cell (ICVC) system of Stolzenburg and Hering (2000). Particles were collected by humidification and impaction and analyzed by in-situ flash vaporization of the evolved vapor compounds. Nitrate concentrations were measured from the evolved vapors using a chemiluminescent monitor equipped with a molybdenum catalyst to convert higher oxides of nitrogen to nitric oxide. The sulfate quantitation was performed by analysis of the evolved sulfur dioxide by UV-fluorescence and total carbon was converted to carbon dioxide and analyzed by nondispersive infrared absorption. A four-cell ICVC system was used to perform simultaneous indoor and outdoor measurements; one pair for nitrate and one pair for a combined carbon and sulfate measurement. The system was located in the living room of the house, however the outdoor sampling cells were housed in an enclosure ventilated with outdoor air to maintain the system at outdoor temperature. The important atmospheric gas phase species of ammonia, nitrous acid, nitric acid and sulfur dioxide were measured using an automated on-line ion chromatograph (IC) system. The IC system collects water-soluble gases using wet denuders, followed by concentration and ion chromatographic analysis based upon the technique of Buhr et al. (1995). The system utilized a dual-channel IC to enable simultaneous automated measurement of both anion and cation species. Denuders were located both inside and outside the house, and provided data with 30minute time resolution. Ventilation rates were measured using a continuous release SF6 tracer gas measurement system using a photoacousitic analyzer (Breul & Kajer, Model 1302). Temperature and relative humidity were measured both inside and outside the house using dual temperature and relative humidity probes (Vaisala HMD70Y) mounted in aspirated shielded enclosures. Experiments were conducted during three intensive measurement periods; October 9-23, 2000, December 11-19, 2000 and January 16-23, 2001. During these intensives, entry into the house was limited to a one-hour period at midday to perform instrument checks and flow calibrations. Instrument control and data acquisition for all instruments were performed from outside the house, allowing for minimal disturbance of the indoor environment. Using the house as a laboratory, a range of conditions was explored during the intensives by manipulating the ventilation rate and indoor-outdoor temperature gradient through natural or mechanical means. The house experienced infiltration rates in the range of 0.2 to 0.5 air changes per hour (ACH) when allowed to operate under naturally occurring conditions. When the doors and windows were opened, the ventilation rate could increase up to 1 ACH. In order to further expand the experimental parameter space to a regime where the residence time for air in the house approached the time required for other processes, such as deposition, to occur, we utilized mechanical ventilation techniques to achieverates in the range of 2 to 6 ACH. The forced-air heating/cooling system was used to provide changes in the indoor/outdoor temperature differential in addition to conditions of either no, continual, or intermittent fan operation. RESULTS AND DISCUSSION Figure 1 shows time series of concentrations for measured total carbon, sulfate and nitrate from the ICVC system during the December intensive measurement period. Figure 1 also shows the ventilation rate measured during the same period. Note that the rate measured during 12/16 PM, 12/17 AM, 12/28 PM and 12/19 AM reflect the high values achieved using mechanically driven ventilation. What is immediately apparent is that there is a great deal of variability in both the indoor and outdoor concentration measurements for these three species. The difference between the indoor and outdoor concentrations is also highly variable. In general, however, the difference between the indoor and outdoor concentration decreases appreciably during periods of high air change rates. This result is intuitive as the characteristic time for particle gain by penetration is significantly greater than that for loss by deposition at these high ventilation rates. Of the three particulate species shown in Fig. 1, sulfate is generally considered to be the most stable upon transport from outdoors to indoors. A forward marching fit of the sulfate data using the time-dependent physical mass balance model results in values of 0.95 for the penetration factor and 0.19 hr for the deposition loss rate, both of which are reasonable (Thatcher, et al, 2002). |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://cloudfront.escholarship.org/dist/prd/content/qt7r451206/qt7r451206.pdf |
| Language | English |
| Access Restriction | Open |
| Subject Keyword | Adobe AIR Aerosol Dose Form Ammonia Anions Automated Clearing House CNS disorder Calibration Carbon Dioxide Cations Chemical vapor deposition Computer cooling Cool - action Cooling Module Device Component DFA minimization Data acquisition Digitorenocerebral Syndrome Dual Email Encephalitis Virus, California Enclosure Device Component Experiment Exposure to Humidity Field research Fluorescence Gases Gradient Heating Instrument - device Instrument control Intermittent Explosive Disorder Ions Jenkins Laser ablation Mechanical ventilation Microsoft Windows Molybdenum Multi-channel memory architecture Nitrates Nitric Acid Nitric Oxide Nitrous Acid Online and offline Oxides Particulate (substance) Particulate Matter Persistent vegetative state Physical vapor deposition Population Parameter Quantitation Real-time transcription Respiration Sampling (signal processing) Spatial variability Sulfate measurement Sulfates, Inorganic Sulfur Dioxide System of measurement Thatcher effect Time series Topography Tracer Trees (plant) ammonium nitrate hearing impairment per hour |
| Content Type | Text |
| Resource Type | Article |
