Michael P. Hannigan

Trends in Fine Particle Concentration and Chemical Composition in Southern California

ABSTRACT Airborne fine particle mass concentrations in Southern California have declined in recent years. Trends in sulfate and elemental carbon (EC) particle concentrations over the period 1982-1993 are consistent with this overall improvement in air quality and help to confirm some of the reasons for the changes that are seen. Fine particle sulfate concentrations have declined as a strict sulfur oxides (SOx) emission control program adopted in 1978 was implemented over time. Fine particle elemental (black) carbon concentrations have declined over a period when newer diesel engines and improved diesel fuels have been introduced into the vehicle fleet. Organic aerosol concentrations have not declined as rapidly as the EC particle concentrations, despite the fact that catalyst-equipped cars having lower particle emission rates were introduced into the vehicle fleet alongside the diesel engine improvements mentioned above. This situation is consistent with the growth in population and vehicle miles traveled in the air basin over time. Fine particle ammonium nitrate in the Los Angeles area atmosphere contributes more than half of the fine aerosol mass concentration on the highest concentration days of the year, emphasizing both the need for accurate aerosol nitrate measurements and the likely importance of deliberate control of aerosol nitrate as a part of any serious further fine particle control program for the Los Angeles area.

Seasonal variability in bacterial and fungal diversity of the near-surface atmosphere.

Bacteria and fungi are ubiquitous throughout the Earths lower atmosphere where they often represent an important component of atmospheric aerosols with the potential to impact human health and atmospheric dynamics. However, the diversity, composition, and spatiotemporal dynamics of these airborne microbes remain poorly understood. We performed a comprehensive analysis of airborne microbes across two aerosol size fractions at urban and rural sites in the Colorado Front Range over a 14-month period. Coarse (PM10-2.5) and fine (PM2.5) particulate matter samples were collected at weekly intervals with both bacterial and fungal diversity assessed via high-throughput sequencing. The diversity and composition of the airborne communities varied across the sites, between the two size fractions, and over time. Bacteria were the dominant type of bioaerosol in the collected air samples, while fungi and plants (pollen) made up the remainder, with the relative abundances of fungi peaking during the spring and summer months. As bacteria made up the majority of bioaerosol particles, we analyzed the bacterial communities in greater detail using a bacterial-specific 16S rRNA gene sequencing approach. Overall, bacterial taxonomic richness and the relative abundances of specific bacterial taxa exhibited significant patterns of seasonality. Likewise, airborne bacterial communities varied significantly between sites and across aerosol size fractions. Source-tracking analyses indicate that soils and leaves represented important sources of bacteria to the near-surface atmosphere across all locations with cow fecal bacteria also representing an important source of bioaerosols at the more rural sites during early fall and early spring. Together, these data suggest that a complex set of environmental factors, including changes in atmospheric conditions and shifts in the relative importance of available microbial sources, act to control the composition of microbial bioaerosols in rural and urban environments.

A Macrophage-Based Method for the Assessment of the Reactive Oxygen Species (ROS) Activity of Atmospheric Particulate Matter (PM) and Application to Routine (Daily-24 h) Aerosol Monitoring Studies

Both short- and long-term exposure to particulate matter (PM) air pollution have been demonstrated to cause increases in cardiovascular disease, cancer, and respiratory disorders. Although the specific mechanisms by which exposure to PM cause these affects are unclear, significant evidence has accumulated to suggest that PM exposure leads to increased inflammation as the result of excessive production of reactive oxygen species (ROS) in critical cell types. In order to better understand how real-world PM exposure causes adverse health effects, there is a need to efficiently integrate metrics of PM toxicity into large scale air monitoring and health effects/epidemiology studies. Here we describe a rapid, inexpensive, method that can be employed to assess the potential of sub-mg masses of PM to generate oxidative stress in alveolar macrophage cells. Importantly, the approach is compatible with routine daily PM sampling programs such as those administered by EPA (Speciation trends network (STN), IMPROVE network, PM2.5 mass monitoring network), allowing for multiple samples to be assessed simultaneously with low volumes and brief exposure periods. We apply the method to a set of water extracts of daily PM2.5 samples (25–350 μ g PM mass) collected in the Denver-Metro area. Variations in the magnitude of the ROS response observed between the samples were only partially explained by differences in mass loading, with the highest levels of ROS being observed in samples collected during the summer months. This assay provides a very useful tool that can be coupled with detailed chemical analysis and statistical models to work towards the goal of attributing PM toxicity to specific real-world chemical sources.

Characterization of organic aerosol in Big Bend National Park, Texas

The Big Bend Regional Aerosol and Visibility Observational (BRAVO) Study was conducted in Big Bend National Park, Texas, July through October 1999. Daily PM2.5 organic aerosol samples were collected on pre-fired quartz fiber filters. Daily concentrations were too low for detailed organic analysis by gas chromatography-mass spectrometry (GC-MS) and were grouped based on their air mass trajectories. A total of 12 composites, each containing 3–10 daily samples, were analyzed. Alkane carbon preference indices suggest primary biogenic emissions were small contributors to primary PM2.5 organic matter (OM) during the first 3 months, while in October air masses advecting from the north and south were more strongly influenced by biogenic sources. A series of trace organic compounds previously shown to serve as particle phase tracers for various carbonaceous aerosol source types were examined. Molecular tracer species were generally at or below detection limits, except for the wood smoke tracer levoglucosan in one composite, so maximum possible source influences were calculated using the detection limit as an upper bound to the tracer concentration. Wood smoke was found not to contribute significantly to PM2.5 OM, with contributions for most samples at <1% of the total organic particulate matter. Vehicular exhaust also appeared to make only minor contributions, with maximum possible influences calculated to be 1–4% of PM2.5 OM. Several factors indicate that secondary organic aerosol formation was important throughout the study, and may have significantly altered the molecular composition of the aerosol during transport.

The temporal lag structure of short-term associations of fine particulate matter chemical constituents and cardiovascular and respiratory hospitalizations.

Background: In air pollution time-series studies, the temporal pattern of the association of fine particulate matter (PM2.5; particulate matter ≤ 2.5 µm in aerodynamic diameter) and health end points has been observed to vary by disease category. The lag pattern of PM2.5 chemical constituents has not been well investigated, largely because daily data have not been available. Objectives: We explored the lag structure for hospital admissions using daily PM2.5 chemical constituent data for 5 years in the Denver Aerosol Sources and Health (DASH) study. Methods: We measured PM2.5 constituents, including elemental carbon, organic carbon, sulfate, and nitrate, at a central residential site from 2003 through 2007 and linked these daily pollution data to daily hospital admission counts in the five-county Denver metropolitan area. Total hospital admissions and subcategories of respiratory and cardiovascular admissions were examined. We assessed the lag structure of relative risks (RRs) of hospital admissions for PM2.5 and four constituents on the same day and from 1 to 14 previous days from a constrained distributed lag model; we adjusted for temperature, humidity, longer-term temporal trends, and day of week using a generalized additive model. Results: RRs were generally larger at shorter lags for total cardiovascular admissions but at longer lags for total respiratory admissions. The delayed lag pattern was particularly prominent for asthma. Elemental and organic carbon generally showed more immediate patterns, whereas sulfate and nitrate showed delayed patterns. Conclusion: In general, PM2.5 chemical constituents were found to have more immediate estimated effects on cardiovascular diseases and more delayed estimated effects on respiratory diseases, depending somewhat on the constituent.

Hallway based automatic indoor floorplan construction using room fingerprints

People spend approximately 70% of their time indoors. Understanding the indoor environments is therefore important for a wide range of emerging mobile personal and social applications. Knowledge of indoor floorplans is often required by these applications. However, indoor floorplans are either unavailable or obtaining them requires slow, tedious, and error-prone manual labor. This paper describes an automatic indoor floorplan construction system. Leveraging Wi-Fi fingerprints and user motion information, this system automatically constructs floorplan via three key steps: (1) room adjacency graph construction to determine which rooms are adjacent; (2) hallway layout learning to estimate room sizes and order rooms along each hallway, and (3) force directed dilation to adjust room sizes and optimize the overall floorplan accuracy. Deployment study in three buildings with 189 rooms demonstrates high floorplan accuracy. The system has been implemented as a mobile middleware, which allows emerging mobile applications to generate, leverage, and share indoor floorplans.

MAQS: a personalized mobile sensing system for indoor air quality monitoring

Most people spend more than 90% of their time indoors; indoor air quality (IAQ) influences human health, safety, productivity, and comfort. This paper describes MAQS, a personalized mobile sensing system for IAQ monitoring. In contrast with existing stationary or outdoor air quality sensing systems, MAQS users carry portable, indoor location tracking sensors that provide personalized IAQ information. To improve accuracy and energy efficiency, MAQS incorporates three novel techniques: (1) an accurate temporal n-gram augmented Bayesian room localization method that requires few Wi-Fi fingerprints; (2) an air exchange rate based IAQ sensing method, which measures general IAQ using only CO2 sensors; and (3) a zone-based proximity detection method for collaborative sensing, which saves energy and enables data sharing among users. MAQS has been deployed and evaluated via user study. Detailed evaluation results demonstrate that MAQS supports accurate personalized IAQ monitoring and quantitative analysis with high energy efficiency.

Coupling between Land Ecosystems and the Atmospheric Hydrologic Cycle through Biogenic Aerosol Pathways

AUTHOR AFFILIATIONS: BARTH, SUN, WIEDINMYER, KARL, KIM, LEVIS, MAHOWALD, MOORE, NANDI, NEMITZ, POTOSNAK, SMITH, AND STROUD—National Center for Atmospheric Research, Boulder, Colorado; MCFADDEN—University of Minnesota, Saint Paul, Minnesota; CHUANG—University of California, Santa Cruz, Santa Cruz, California; COLLINS—Texas A&M University, College Station, Texas; GRIFFIN—University of New Hampshire, Durham, New Hampshire; HANNIGAN—University of Colorado, Boulder, Colorado; LASHER-TRAPP—Purdue University, West Lafayette, Indiana; LITVAK—University of Texas, Austin, Texas; NENES—Georgia Institute of Technology, Atlanta, Georgia; RAYMOND—Bucknell University, Lewisburg, Pennsylvania; STILL—University of California, Santa Barbara, Santa Barbara, California CORRESPONDING AUTHOR: Dr. Mary Barth, NCAR/MMM, P.O. Box 3000, Boulder, CO 80307 E-mail: barthm@ucar.edu

Source Contributions to the Mutagenicity of Urban Particulate Air Pollution

Abstract Using organic compounds as tracers, a chemical mass balance model was employed to investigate the relationship between the mutagenicity of the urban organic aerosol sources and the mutagenicity of the atmospheric samples. The fine particle organic mass concentration present in the 1993 annual average Los Angeles-area composite sample was apportioned among eight emission source types. The largest source contributions to fine particulate organic compound mass concentration were identified as smoke from meat cooking, diesel-powered vehicle exhaust, wood smoke, and paved road dust. However, the largest source contributions to the mutagenicity of the atmospheric sample were natural gas combustion and diesel-powered vehicles. In both the human cell and bacterial assay systems, the combined mutagenicity of the composite of primary source effluents predicted to be present in the atmosphere was statistically indistinguishable from the mutagenicity of the actual atmospheric sample composite. Known primary emissions sources appear to be capable of emitting mutagenic organic matter to the urban atmosphere in amounts sufficient to account for the observed mutagenicity of the ambient samples. The error bounds on this analysis, however, are wide enough to admit to the possible importance of additional mutagenic organics that are formed by atmospheric reaction (e.g., 2-nitrofluoranthene has been identified as an important human cell mutagen in the atmospheric composite studied here, accounting for ∼1% of the total sample mutagenic potency).

Bacterial Mutagenicity of Urban Organic Aerosol Sources in Comparison to Atmospheric Samples

The bacterial mutagenicity of a comprehensive set of urban particulate air pollution source samples is examined using the Salmonella typhimurium forward mutation assay. Each of the combustion source samples examined, including the exhaust from catalyst-equipped autos, noncatalyst autos, heavy-duty diesel trucks, plus natural gas, distillate oil, and wood combustion sources, is mutagenic in this assay, with a response per microgram of organic carbon in these samples generally greater than that of cigarette smoke aerosol. The noncombustion source samples tested generally are not mutagenic at the levels examined. The specific mutagenicity (mutant fraction per microgram of organic carbon) of ambient aerosol samples collected in southern California is compared to a weighted average of the specific mutagenicity of the primary source samples assembled in proportion to their emission rates in the Los Angeles area. In most cases where a comparison can be made, the specific mutagenicity of the source composites and the ambient samples are of similar magnitude, with the exception that the -PMS mutagenicity of the aerosol at Long Beach, CA, during the first half of the calendar year 1982 and at Azusa, CA, during the April-June 1982 period is much higher than can be explained by direct emissions from the sources studied here.