Bok Haeng Baek

Measurement and Analysis of the Relationship between Ammonia, Acid Gases, and Fine Particles in Eastern North Carolina

Abstract An annular denuder system, which consisted of a cyclone separator; two diffusion denuders coated with sodium carbonate and citric acid, respectively; and a filter pack consisting of Teflon and nylon filters in series, was used to measure acid gases, ammonia (NH3), and fine particles in the atmosphere from April 1998 to March 1999 in eastern North Carolina (i.e., an NH3−rich environment). The sodium carbonate denuders yielded average acid gas concentrations of 0.23 μg/m3 hydrochloric acid (standard deviation [SD] ± 0.2 μg/m3); 1.14 μg/m3 nitric acid (SD ± 0.81 μg/m3), and 1.61 μg/m3 sulfuric acid (SD ± 1.58 μg/m3). The citric acid denuders yielded an average concentration of 17.89 μg/m3 NH3 (SD ± 15.03 μg/m3). The filters yielded average fine aerosol concentrations of 1.64 μg/m3 ammonium (NH4 +;SD ± 1.26 μg/m3); 0.26 μg/m3 chloride (SD ± 0.69 μg/m3), 1.92 μg/m3 nitrate (SD ± 1.09 μg/m3), and 3.18 μg/m3 sulfate (SO4 2−; SD ± 3.12 μg/m3). From seasonal variation, the measured particulates (NH4 +,SO4 2−, and nitrate) showed larger peak concentrations during summer, suggesting that the gas-to-particle conversion was efficient during summer. The aerosol fraction in this study area indicated the domination of ammonium sulfate particles because of the local abundance of NH3, and the long-range transport of SO4 2− based on back trajectory analysis. Relative humidity effects on gas-to-particle conversion processes were analyzed by particulate NH4 + concentration originally formed from the neutralization processes with the secondary pollutants in the atmosphere.

Current and Future Particulate-Matter-Related Mortality Risks in the United States from Aviation Emissions During Landing and Takeoff

Demand for air travel is projected to increase in the upcoming years, with a corresponding influence on emissions, air quality, and public health. The trajectory of health impacts would be influenced by not just emissions growth, but also changes in nonaviation ambient concentrations that influence secondary fine particulate matter (PM(2.5) ) formation, population growth and aging, and potential shifts in PM(2.5) concentration-response functions (CRFs). However, studies to date have not systematically evaluated the individual and joint contributions of these factors to health risk trajectories. In this study, we simulated emissions during landing and takeoff from aircraft at 99 airports across the United States for 2005 and for a 2025 flight activity projection scenario. We applied the Community Multiscale Air Quality (CMAQ) model with the Speciated Modeled Attainment Test (SMAT) to determine the contributions of these emissions to ambient concentrations, including scenarios with 2025 aircraft emissions and 2005 nonaviation air quality. We combined CMAQ outputs with PM(2.5) mortality CRFs and population projections, and evaluated the influence of changing emissions, nonaviation concentrations, and population factors. Given these scenarios, aviation-related health impacts would increase by a factor of 6.1 from 2005 to 2025, with a factor of 2.1 attributable to emissions, a factor of 1.3 attributable to population factors, and a factor of 2.3 attributable to changing nonaviation concentrations which enhance secondary PM(2.5) formation. Our study emphasizes that the public health burden of aviation emissions would be significantly influenced by the joint effects of flight activity increases, nonaviation concentration changes, and population growth and aging.

Observation based analysis for the determination of equilibrium time constant between ammonia, acid gases, and fine particles

Experimental measurements of ammonia, acid gases, and the inorganic components of atmospheric aerosols were made at a commercial hog farm in eastern North Carolina from May 1998 to June 1999 by an annular denuder system (ADS). The ADS consisted of a cyclone separator, one diffusion denuder coated with sodium carbonate, another diffusion denuder with citric acid, and a filter pack containing Teflon and nylon filters in series. The equilibrium time constant for transfer between ammonia, acid gases, and aerosol phase of ammonium nitrate and ammonium chloride was determined based on kinetic rate constants (kN as the rate constant of ammonium nitrate aerosol: 2.04 × 10-4 m³/µmole/sec; kCl as the rate constant of ammonium chloride aerosol: 3.44 × 10-4 m³/µmole/sec) and the observed inorganic components of atmospheric aerosols. The equilibrium time constant was determined based on kinetic rate constants and the observed inorganic components of atmospheric aerosols. The equilibrium time constant has a wide range of values, with an average value of 15.26 (±10.94) minutes for ambient equilibrium time between ammonia, nitric acid gas and ammonium nitrate aerosol; and 8.22 (±6.81) minutes for ammonia, hydrochloric acid, and ammonium chloride. Significant correlations were determined between comparisons of equilibrium time constant estimates with meteorological parameters, such as ambient temperature and relative humidity. The predicted chemical compositions in the particle by EQUISOLV II Model are in good agreement with the observed chemical composition at the experimental site.

A preliminary review of gas-to-particle conversion monitoring and modelling efforts in the USA

Ammonia and inorganic acid gases emitted from livestock and poultry operations, manure treatment, handling and application can affect air quality by the formation of secondary fine particles. The process of gas-to-particle conversion (GTPC) of relatively short-lived gaseous ammonia to more persistent fine particles can affect local and regional air quality far away from the agricultural sources. This study focused on understanding the phenomenon and related problems of the GTPC process between ammonia, acid gases and fine particles in the atmosphere. We discuss the knowledge of PM measurement technologies with their uncertainties and introduce the most recent aerosol models available developed to simulate the equilibrium partitioning of inorganic compounds between the gas and aerosol phases. We discuss the development and evaluate progress on ambient PM research using 3D air quality models and demonstrate the importance of the GTPC process concerning the contribution of ammonia on fine PM formation in agricultural areas.

Guidance for Quantifying the Contribution of Airport Emissions to Local Air Quality

This report is a guide for airport operators on effective procedures for using air quality models in combination with on-site measurement equipment to prepare a comprehensive assessment of air pollutant concentrations in the vicinity of airports. It is designed to help practitioners generate information desired by local communities as they seek to develop more detailed local air quality assessments as well as respond to regulatory needs, including those of the National Environmental Policy Act (NEPA). The guide provides in-depth information on the capabilities and limitations of modeling and measurement tools, adding to an increasing knowledge base concerning preparation of air quality assessments near airports. Starting with the Federal Aviation Administrations (FAAs) regulatory EDMS/AEDT, it describes how best to use available models, in combination with potential on-site monitoring programs, to conduct air quality assessments. Detailed information on the monitoring campaigns and modeling assessments is included in a set of appendices that accompany the guide. The appendices (available in CRP-CD-115) describe the models tested and the various equipment used to collect data, the rationale behind the selection of Washington Dulles International Airport as a case study application, and the components and steps involved in the measurement campaigns, and include an assessment of the various model outputs.

Projecting wildfire emissions over the south-eastern United States to mid-century

Wildfires can impair human health because of the toxicity of emitted pollutants, and threaten communities, structures and the integrity of ecosystems sensitive to disturbance. Climate and socioeconomic factors (e.g. population and income growth) are known regional drivers of wildfires. Reflecting changes in these factors in wildfire emissions estimates is thus a critical need in air quality and health risk assessments in the south-eastern United States. We developed such a methodology leveraging published statistical models of annual area burned (AAB) over the US Southeast for 2011–2060, based on county-level socioeconomic and climate projections, to estimate daily wildfire emissions in selected historical and future years. Projected AABs were 7 to 150% lower on average than the historical mean AABs for 1992–2010; projected wildfire fine-particulate emissions were 13 to 62% lower than those based on historical AABs, with a temporal variability driven by the climate system. The greatest differences were in areas of large wildfire impacts from socioeconomic factors, suggesting that historically based (static) wildfire inventories cannot properly represent future air quality responses to changes in these factors. The results also underscore the need to correct biases in the dynamical downscaling of wildfire climate drivers to project the health risks of wildfire emissions more reliably.

A Multiscale Modeling Study to Assess Impacts of Full-Flight Aircraft Emissions on Upper Troposphere and Surface Air Quality

Aviation is a unique anthropogenic source with 4-dimensional varying emissions, emitting 90 % of their emissions in upper troposphere at cruise altitudes (9–12 km). Aircraft emissions budgets in upper troposphere lower stratosphere (UTLS) region and their potential impacts on upper troposphere and surface air quality are not well understood. The key objective of this study is to characterize the aircraft emissions during full-flight activity in regional and hemispheric modeling scales, and assess their impacts on upper tropospheric chemistry and surface air quality. Using detailed spatio-temporal characterization of aircraft emissions along with other background emissions in the modeling domains, we studied incremental impacts of aircraft emissions focusing mainly on O3, NOx and PM2.5 species. Comparison of modeling results with aircraft measurements showed improvement of model performance due to enhanced modeling platform and consideration of cruise altitude aviation emissions in the upper troposphere.

An Investigation of the Impacts of Aviation Emissions on Future Air Quality and Health

Recent estimates of the growth in demand for aviation indicate that passenger counts may double or even triple by the year 2025, with a corresponding projected increase in emissions from the aviation sector. This would contribute to approximately proportional increases in concentrations and health effects if other factors were unchanging, but background emissions from non-aviation anthropogenic sources are generally expected to decrease due to several emissions control measures that are likely to be in place, and population size and age distribution will change over time. In this study, we evaluated changes in air quality and health risk due to growth in aviation activities from the year 2005 to 2025, focusing on 99 major U.S. airports with aircraft activity data for landing and takeoff (LTO) based on Terminal Area Forecasts (TAFs) developed for a sample growth scenario under the Next Generation Air Transportation System (NextGen) for 2025. We performed four annual simulations using the MM5-SMOKE-CMAQ modeling system for the year 2005 and 2025, with and without aircraft emissions. We obtained non-aviation emissions for 2005 from EPA’s 2005 National Emissions Inventory (NEI), and projected these to the year 2025. In performing the health risk analyses, we applied the EPA’s Speciated Modeled Attainment Test (SMAT) to the CMAQ results, and compared the air quality and health risk results on a pre-SMAT and post-SMAT basis. Our findings illustrated that each of the time-varying components – background concentrations, emissions, and population patterns – contributes significantly to growth in projected health risks over time, with significant differences in trends by particle constituent and region of the country. The relative importance of various particle constituents also depended significantly on the SMAT process, although secondary sulfate and nitrate particles dominated health risk in all scenarios. These conclusions provide an indication of the factors influencing health risk over time and the resulting areas in which interventions may be most effective.

Comparing Monitoring-Based and Modeling-Based Approaches for Evaluating Black Carbon Contributions from a U.S. Airport

Black carbon (BC) is a key component of fine particulate matter that is emitted from aircraft and other combustion sources at airports. Understanding the contribution of aviation activity to ambient BC is important given the projected growth in aviation transport and decrease in emissions from other anthropogenic sources, but there are limitations in the various approaches conventionally used for source attribution. In this study, we evaluate three contrasting approaches to assess the contribution of aviation activity to BC concentrations near a small regional airport in Rhode Island, USA. First, we apply a previously developed regression model utilizing continuous BC concentrations measured at five monitoring sites and predictors such as real-time flight activity (departures and arrivals) and meteorological data, including mixing height, wind speed and direction. Second, we used AERMOD to model all airport sources of BC. Third, we used the Community Multiscale Air Quality (CMAQ) model, a comprehensive chemistry-transport air quality model. We included emissions estimates of all airport activity using an enhanced representation within the lowest 10,000 ft. inclusive of the landing and takeoff (LTO) cycle (the lowest 3,000 ft.) in the modeling system, along with other emissions from all other background sources. Median contribution estimates from the regression model indicate that flight activity contribute to approximately 24–28% of the observed BC concentrations at these five locations. The CMAQ and AERMOD based results show a much smaller contribution, in the range of 2–5% of the observed BC concentrations. We present possible explanations for these discrepancies, using a detailed analysis at different temporal scales at all five locations, and consider possible refinements to each approach. Our findings help to highlight the strengths and weaknesses of various source attribution approaches in the context of aviation emissions and other settings where it is of interest to infer local contributions to ambient concentrations.