Comparison of Short-Term Variations (15-Minute Averages) in Outdoor and Indoor PM2.5 Concentrations

ABSTRACT

Measurements of 15-min average PM_2.5 concentrations were made with a real-time light-scattering instrument at both outdoor (central monitoring sites in three communities) and indoor (residential) locations over two seasons in the Minneapolis-St. Paul metropolitan area. These data are used to examine within-day variability of PM_2.5 concentrations indoors and outdoors, as well as matched indoor-to-outdoor (I/O) ratios. Concurrent gravimetric measurements of 24-hr average PM_2.5 concentrations were also obtained as a way to compare real-time measures with this more traditional metric. Results indicate that (1) within-day variability for both indoor and outdoor 15-min average PM_2.5 concentrations was substantial and comparable in magnitude to day-to-day variability for 24hr average concentrations; (2) some residences exhibited substantial variability in indoor aerosol characteristics from one day to the next; (3) peak values for indoor short-term (15-min) average PM_2.5 concentrations routinely exceeded 24-hr average outdoor values by factors of 3-4; and (4) relatively strong correlations existed between indoor and outdoor PM_2.5 concentrations for both 24-hr and 15-min averages.     

Influence of phosphorus and trace metals in biofilters treating gaseous VOCs using a novel irrigation system

ABSTRACT

Although the appropriate supply of nutrients has been extensively researched, more information is required on the effects of nutrients in treating gaseous volatile organic compounds (VOCs) in biofiltration. In this study, the effects of phosphorous and trace metals on gaseous toluene and methyl ethyl ketone (MEK) removal were investigated. The transfer of nutrients from the irrigation liquid to the packed bed, and the consumption and holding amount of nutrients in the packing material were observed during biofiltration. Under conditions of 20–24 s of empty bed residence time, MEK removal was 95% or more in all conditions of the biofiltration reactors, whereas toluene removal was affected by the operating conditions of the reactors. Consumption ratio of phosphorus to carbon was from 1.7 × 10^?4 to 1.1 × 10^?3 in the steady state of VOC removal under the conditions of this study. When gaseous VOC treatment was restarted after nine days of shutdown, a significant decline in toluene removal was observed by the reactor in which phosphorus supply was approximately one fifth of the amount in another reactor. Two types of irrigation systems, soaking and spraying, were compared and soaking irrigation achieved a more even distribution of nutrients held inside the packed bed. Soaking irrigation was expected to lead to higher VOC removal capacity by this distribution effect of nutrients, but toluene removal in the reactor with this irrigation was lower than that in the reactor with spraying irrigation. One of the possible reasons for this was the inhibition of nutrients transfer in the bottom part of the reactor. The trend of transfer in all ingredients from the irrigation liquid to the packed bed was synchronized on the whole; however, this transfer relatively tended to be high in nitrate and sodium and low in ammonium and phosphate.

Implications: A major concern about using biofiltration systems to treat VOCs is the uncertainty regarding the appropriate nutrient supply to the filter bed to preserve microbial activity. This study showed that all the elements, except nitrogen, were retained sufficiently in the filter bed when a proper composition of nutrient solution was used for irrigation; however, phosphate addition may be needed when restarting a reactor from a prolonged period of shutdown. Distinct differences in the amount of transfer to the filter bed for different ingredients are probable, and may have to be taken into account when operating biofiltration reactors.     

Evaluation of particulate matter abatement strategies for almond harvest

Almond harvest accounts for substantial PM10 (particulate matter [PM] < or =10 microm in nominal aerodynamic diameter) emissions in California each harvest season. This paper evaluates the effects of using reduced-pass sweepers and lower harvester separation fan speeds (930 rpm) on lowering PM emissions from almond harvesting operations. In-canopy measurements of PM concentrations were collected along with PM concentration measurements at the orchard boundary; these were used in conjunction with on-site meteorological data and inverse dispersion modeling to back-calculate emission rates from the measured concentrations. The harvester discharge plume was measured as a function of visible plume opacity during conditioning operations. Reduced-pass sweeping showed the potential for reducing PM emissions, but results were confounded because of differences in orchard maturity and irrigation methods. Fuel consumption and sweeping time per unit area were reduced when comparing a reduced-pass sweeper to a conventional sweeper. Reducing the separation fan speed from 1080 to 930 rpm led to reductions in PM emissions. In general, foreign matter levels within harvested product were nominally affected by separation fan speed in the south (less mature) orchard; however, in samples conditioned using the lower fan speed from the north (more mature) orchard, these levels were unacceptable.     

Determining residential firewood consumption

Household firewood use has become increasingly popular in the United States over the past few years. Significant problems remain in estimating firewood consumption. Methods of determining the amount of wood consumed vary from state to state. Units used for measuring firewood vary, but the cord remains the researcher's favorite. Factors used for converting other units, such as pickup truck loads to cords also vary. People who do not use firewood are less likely to respond to mailed surveys, resulting in potential overestimates of statewide consumption. This paper identifies some problems associated with estimating household firewood consumption and recommends methods of dealing with them.     

Evaluation and valuation of wildlife resources

Issues of resource conservation and development are essentially about choice between alternative uses of land. Resource evaluation in rural planning has usually been based on assessments of land quality or capability in relation to a variety of alternative uses. In the case of wildlife, choices have to be made as to whether the wildlife resource is worth conserving at all and if so, which sites should be used. Considerable efforts have been made to rationalise, improve and make explicit the way in which choices are made, and this paper reviews the current position and draws attention to issues and developments which could lead to improvements in current practice.     

Bioproduction strategies for rare hexose sugars

A new strategy for the bioproduction of all ketohexoses was developed using hexitols as intermediates. Biocatalysts used to employ the strategy were D-tagatose 3-epimerase, which epimerizes ketohexoses at the C-3 position, and oxidoreductases, which catalyze oxidation-reduction reactions between ketohexoses and the corresponding hexitols. Arranging all the ketohexoses and hexitols in a symmetric ring and connecting them with 20 biochemical reactions, I was able to construct a design for the bioproduction of all the rare ketohexoses. Various aldose isomerases transform ketohexoses into the corresponding aldohexoses, so the strategy is useful for the bioproduction of all the rare hexose sugars. Furthermore, the design revealed that there are four routes to the L-hexose world from the D-hexose one.     

Interrelationship of macropores and subsurface drainage for conservative tracer and pesticide transport

Macropore flow results in the rapid movement of pesticides to subsurface drains, which may be caused in part by a small portion of macropores directly connected to drains. However, current models fail to account for this direct connection. This research investigated the interrelationship between macropore flow and subsurface drainage on conservative solute and pesticide transport using the Root Zone Water Quality Model (RZWQM). Potassium bromide tracer and isoxaflutole, the active ingredient in BALANCE herbicide [(5-cyclopropyl-4-isoxazolyl) [2(methylsulfonyl)-4-(trifluoromethyl)phenyl] methanone], with average half-life of 1.7 d were applied to a 30.4-ha Indiana corn (Zea mays L.) field. Water flow and chemical concentrations emanating from the drains were measured from two samplers. Model predictions of drain flow after minimal calibration reasonably matched observations (slope = 1.03, intercept = 0.01, and R(2) = 0.75). Without direct hydraulic connection of macropores to drains, RZWQM under predicted bromide and isoxaflutole concentration during the first measured peak after application (e.g., observed isoxaflutole concentration was between 1.2 and 1.4 mug L(-1), RZWQM concentration was 0.1 mug L(-1)). This research modified RZWQM to include an express fraction relating the percentage of macropores in direct hydraulic connection to drains. The modified model captured the first measured peak in bromide and isoxaflutole concentrations using an express fraction of 2% (e.g., simulated isoxaflutole concentration increased to 1.7 mug L(-1)). The RZWQM modified to include a macropore express fraction more accurately simulates chemical movement through macropores to subsurface drains. An express fraction is required to match peak concentrations in subsurface drains shortly after chemical applications.