Grantee Research Project Results
Final Report: Projecting Pollen Allergens and Their Health Implications in a Changing World
EPA Grant Number: R834358Title: Projecting Pollen Allergens and Their Health Implications in a Changing World
Investigators: Flagan, Richard , Gilliland, Frank D. , VanReken, Timothy M. , Guenther, Alex , Lamb, Brian , Chung, Sandra
Institution: California Institute of Technology , University of California - Los Angeles , Washington State University , National Center for Atmospheric Research
Current Institution: California Institute of Technology , National Center for Atmospheric Research , University of California - Los Angeles , Washington State University
EPA Project Officer: Chung, Serena
Project Period: October 1, 2009 through September 30, 2012 (Extended to September 30, 2013)
Project Amount: $900,000
RFA: Climate Change and Allergic Airway Disease (2008) RFA Text | Recipients Lists
Research Category: Climate Change , Human Health
Objective:
The overall goal of this project was to improve our understanding of linkages among global change, pollen occurrence, and respiratory health impacts through a combination of focused experimental studies, modeling, and statistical analysis that will ultimately lead to the integration of pollen allergen and population health outcome models into an existing air quality modeling framework. These models have been designed to estimate the impacts that these contaminants may have on allergic airway disease. Key scientific questions addressed in the research include: (i) How do biological sources respond to a changing climate, in terms of pollen production and the conversion of pollen to respirable allergenic material? (ii) How will these species-specific responses combine with land use, population, and climatic changes to impact the levels of atmospheric allergens in the future? (iii) What links exist between airborne pollen levels, concentrations of respirable allergenic material, and human allergenic response? (iv) What will be the response of the US population to these future projected allergen levels, including the
synergistic response due to projected allergen and pollutant levels?
Summary/Accomplishments (Outputs/Outcomes):
Through a combination of measurements and modeling, this study has established aframework for prediction of pollen exposures that can be used to probe the influence of climate change on allergic airway disease. A key development of this project is the development of framework for modeling pollen production and release as an input into a regional emission and transport model. Building upon the extensive literature on pollen modeling, the Simulator of the Timing and Magnitude of Pollen Season (STaMPS) predicts both the timing of pollen emissions, and the quantities of pollen released as a result of meteorological influences on emission. The model has been developed and validated for the western U.S., a region that has received relatively little attention in previous studies of airborne pollen. In particular, STaMPS has been applied to the southern California area where Mediterranean climate and an abundance of both native and non-native plants account for much of the allergen burden of the atmospheric aerosol. Within STaMPS, the thermal-time approach is applied to predict the timing of flowering based upon growing degree days (GDD), with the chill-heating model being used to account for the chilling requirements for flowering of trees and grasses with such
requirements. The pollen potential, which is defined as the quantity of pollen produced per unit area of land, is derived from measures of pollen production per plant, and the associated areal density of the relevant plants. Prediction of the fraction of pollen released to the air is based upon phenomenological models of pollen entrainment as a function of meteorological conditions.
The empirical coefficients for these models for different genera have been derived from local pollen data and literature phenology and pollen count reports. Significant adjustments to literature values were required to account for the effects of environmental stresses on non-native plants. As such, the parameters must be viewed as preliminary, and location-specific. With these caveats, STaMPS was developed and validated using long-term pollen data from the pollen counting station in Pasadena, the only pollen counting station that has been regularly operated within Los Angeles county during the past decade. These data were augmented by measurements that were made in eight southern California communities where respiratory health evaluations of school children were being conducted as part of the University of Southern California Children’s Heath Study during spring, 2010. The former measurements provided trends in pollen counts over the course of a decade; the latter ones provide a test of the spatial heterogeneity of pollen exposures.
The STaMPS pollen model has been integrated into a regional-scale pollen emission and transport modeling framework that treats allergenic pollens as non-reactive tracers within the WRF/CMAQ air-quality modeling system. STaMPS model generates a daily pollen pool that can then be emitted into the atmosphere by wind. The STaMPS is driven by species-specific meteorological (temperature and/or precipitation) threshold conditions and is designed to be flexible with respect to its representation of vegetation species and plant functional types. The pollen modeling framework was compared to measurements in southern California for the period from March to June 2010, a period that coincided with observations by the University of Southern California’s Children’s Health Study (CHS). CHS measurments included ambient O3, NO2, PM2.5, and pollen count, as well as measurements of exhaled nitric oxide and standardized symptoms questionnaires from study participants. Two nesting domains with horizontal resolutions of 12 km and 4 km were constructed, and six representative allergenic pollen genera were included: birch tree, walnut tree, mulberry tree, olive tree, oak tree, and brome grasses. Under the current parameterization scheme, the modeling framework tends to underestimate walnut and peak oak pollen concentrations, and tends to overestimate grass pollen concentrations. The model shows reasonable agreement with observed concentrations of key allergens during that period, i.e., birch, olive, and mulberry. Sensitivity studies suggest that the estimation of the pollen pool is a major source of uncertainty for simulated pollen concentrations. Achieving agreement between emission modeling and observed pattern of pollen release is the key for successful pollen concentration simulations.
The pollen data used in the development and validation of STaMPS and its implementation within the WRF/CMAQ air quality modeling system were derived from measurements in Pasadena, CA over a decade by members of the research team, and shorter duration measurements made during March through June, 2010 in support of the Children’s Health Study. It was expected that these data could be augmented with data from the only national pollen database in the U.S., that of the National Allergy Bureau that assembles data that are generated by volunteer pollen counters. Unfortunately, access to those additional data was severely restricted as this study began, even though Caltech was providing data to the NAB. Thus, in spite of numerous efforts to obtain data for additional locations from the NAB, only the pollen count data generated by the research team was available to this study.
Efforts to establish dose-response functions for pollen allergen exposure leveraged support under this project with the University of Southern California Children’s Health Study, which performed health evaluations on 950 children in eight southern California communities, including forced exhalation nitric oxide (FeNO) measurements that were conducted using American Thoracic Society guidelines, questionnaires, and in-person interviews with USC staff to provide data on recent asthma-related outcomes (e.g., asthma symptoms and medication use). During the weeks prior to, and during health evaluations, 6 Burkard samplers were used to collect pollen samples in each of the eight study communities, providing data on the intra- and inter-community spatial variation of pollen concentrations as well as exposures in the study communities. The health evaluations revealed sensitivity of a large fraction of the study cohort to pollens that were not in season at the time of the health evaluations, and differential sensitivities to sagebrush, and specific grasses (80% sensitivity to Timothy grass, and similar sensitivity to Bermunda grass), but less so to the brome grass which appears prominently in the pollen simulations. Funds were redirected to add additional allergenic species to the pollen model, and to extend the modeling to cover a full annual cycle. Further work will be required to incorporate the full data set into dose-response evaluations, and, therefore, to predict the health consequences of changing pollen exposures due to climate change.
Conclusions:
A key conclusion of this study is that the pollen data in the U.S. is inadequate. The present pollen record relies on a medical association. Most of those stations are
associated with allergy clinics that perform pollen counts in support of clinical practice. While sufficient to inform patients and guide local medical practice, the present data were not designed to support fundamental research. This approach to providing these important public health data differs from that in a number of other countries where public agencies are charged with providing pollen exposure data, e.g., the Met Office in the U.K, the German Meteorological Service in cooperation with the Pollen Information Service, the University of Turku in Finland, and Le Réseau National de Surveillance Aérobiologique (R.N.S.A.) in France, among other participants in the European aeroallergen network. The data generated by these national networks is subjected to quality assurance/quality control processes that the U.S. network lacks, and provide a resource for both medical practice and scientific research. A national pollen database is sorely needed in the U.S. The cost of measuring pollen is so high that fewer than 90 pollen-counting stations contribute to the NAB database. Methods for counting pollen have not changed significantly since the Hirsch sampler (the predecessor for the Burkard sampler used in this study) was introduced in the 1950s. Pollen is impacted onto an adhesive-coated tape using a single-stage impactor. That tape is then transferred to microscope slides for manual pollen identification and counting. Due to the time required for pollen counting, only a small fraction of the slide is analyzed, leading to poor counting statistics. Moreover, the recommended practice of counting the pollen in one or two lines that are selected by the counter along the length of the slide introduces systematic biases to the pollen count.
Under separate support, the Caltech team members have developed the Automated Pollen Identification and Counting System (APICS) that uses computerized microscopy to scan slides, and computer vision methods for pollen identification. This system enables routine analysis of entire daily pollen slides, improving the statistical significance of the measurements (reducing uncertainty in pollen count by a factor of ~3). Analysis of whole-slide data reveals that recommended and accepted practices for manual pollen counting systematically overestimates concentrations. Current models, including STaMPS, only attempt to predict the presence and concentrations of whole pollen, but pollen is too large to penetrate into the lower airways where bronchoconstriction occurs. Upon immersion into liquid water, or exposure to high thermodynamic activity (relative humidity, RH) of water vapor causes water to diffuse into the pollen grains, increasing turgor in the cells, which can cause pollen grains to rupture. Laboratory experiments have demonstrated pollen rupture due to this osmotic shock for a wide range of species. Moreover, antibody assays of respirable particles have detected antigens associated with birch, rye grass, and chinese elm in the ambient aerosol. As part of this project, controlled laboratory experiments have been conducted to advance fundamental understanding of pollen rupture, and to facilitate the development of predictive models. Wheat pollen (Triticum aestivicum) was selected for this study since ongoing research at Washington State University makes this pollen
available for study throughout the year. Freshly harvested pollen grains were continuously observed by optical microscopy while being exposed to controlled relative humidity for periods as long as several days. At a relative humidity of 85%, pollen rupture began after a few minutes, with the fraction of grains that ruptured increasing to a plateau of about 1000 minutes. Higher RH reduced the time to rupture, reaching 100% in about 300 minutes at 95% RH. These data provide the base for a phenomenological model of pollen rupture, which is currently under development. With that framework, the experimental protocol that has been developed can then be used to extend the analysis to species that are more closely linked to allergic airway disease.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 13 publications | 2 publications in selected types | All 2 journal articles |
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Duhl TR, Zhang R, Guenther A, Chung SH, Salam MT, House JM, Flagan RC, Avol EL, Gilliland FD, Lamb BK, VanReken TM, Zhang Y, Salathe E. The Simulator of the Timing and Magnitude of Pollen Season (STaMPS) model: a pollen production model for regional emission and transport modeling. Geoscientific Model Development Discussions 2013;6(2):2325-2368. |
R834358 (2012) R834358 (Final) |
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Zhang R, Duhl T, Salam MT, House JM, Flagan RC, Avol EL, Gilliland FD, Guenther A, Chung SH, Lamb BK, VanReken TM. Development of a regional-scale pollen emission and transport modeling framework for investigating the impact of climate change on allergic airway disease. Biogeosciences Discussions 2013;10(3):3977-4023. |
R834358 (2012) R834358 (Final) |
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Supplemental Keywords:
pollen; respirable allergen; pollen fragmentation; respiratory health; asthma; climate change; vegetation distribution, RFA, Health, Air, climate change, Air Pollution Effects, Risk Assessments, Atmosphere, environmental monitoring, pollen, allergic airway disease, respiratory illnessProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.