A preliminary look at source-receptor relationships in the Texas-Mexico border area

Several factors have recently caused visibility impairment at Big Bend National Park, TX, to be of interest. Analyses of historical data collected there have shown that visibility is poorer and fine particle concentrations are higher at Big Bend than at other monitored Class I areas in the western United States. In addition, air masses frequently arrive there after crossing Mexico, where emissions are not well known. During September and October 1996, a field study was undertaken to begin examining the aerosol, visibility, and meteorology on both sides of the border. Results indicate that, during the study, the largest fractions of fine mass and light extinction at Big Bend were due to sulfates and the trace elements most closely associated with sulfate particles were Na and Se. Based on back trajectory modeling and the spatial, temporal, and inter-species relationships in the fine particle concentrations measured during the study, sulfates arrived at the park from both Mexico and the United States. Se was higher in Texas than in Northern Mexico, while V, Pb, Zn, Ni, and Mn were on average much higher in Mexico.     

A Preliminary Look at Source-Receptor Relationships in the Texas-Mexico Border Area

ABSTRACT

Several factors have recently caused visibility impairment at Big Bend National Park, TX, to be of interest. Analyses of historical data collected there have shown that visibility is poorer and fine particle concentrations are higher at Big Bend than at other monitored Class I areas in the western United States. In addition, air masses frequently arrive there after crossing Mexico, where emissions are not well known. During September and October 1996, a field study was undertaken to begin examining the aerosol, visibility, and meteorology on both sides of the border. Results indicate that, during the study, the largest fractions of fine mass and light extinction at Big Bend were due to sulfates and the trace elements most closely associated with sulfate particles were Na and Se. Based on back trajectory modeling and the spatial, temporal, and inter-species relationships in the fine particle concentrations measured during the study, sulfates arrived at the park from both Mexico and the United States. Se was higher in Texas than in Northern Mexico, while V, Pb, Zn, Ni, and Mn were on average much higher in Mexico.     

Interpretation of trends of PM2.5 and reconstructed visibility from the IMPROVE network

Under the IMPROVE visibility monitoring network, federal land managers have monitored visibility and fine particle concentrations at 29 Class I area sites (mostly national parks and wilderness areas) and Washington, DC since 1988. This paper evaluates trends in reconstructed visibility and fine particles for the 10th (best visibility days), 50th (average visibility days), and 90th (worst visibility days) percentiles over the nine-year period from 1988-96. Data from these sites provides an indication of regional trends in air quality and visibility resulting from implementation of various emission reduction strategies.     

Interpretation of Trends of PM25 and Reconstructed Visibility from the IMPROVE Network

ABSTRACT

Under the IMPROVE visibility monitoring network, federal land managers have monitored visibility and fine particle concentrations at 29 Class I area sites (mostly national parks and wilderness areas) and Washington, DC since 1988. This paper evaluates trends in reconstructed visibility and fine particles for the 10th (best visibility days), 50th (average visibility days), and 90th (worst visibility days) percentiles over the nine-year period from 1988-96. Data from these sites provides an indication of regional trends in air quality and visibility resulting from implementation of various emission reduction strategies.     

Chemical species’ contributions to the upper extremes of aerosol fine mass

Frequency distributions of the major chemical components of aerosol fine mass are shown to illustrate the respective species’ contributions to the range of observed fine particle mass concentration. The magnitude of a species’ contribution to the upper extremes of aerosol fine mass is relevant to control scenarios that seek to improve worst day fine particle conditions, or in many cases worst day visibility. We summarize the relative contributions of fine particle sulfate, nitrate, carbon, and soil plus sea salt to the upper extremes of aerosol fine mass based on Interagency Monitoring of PROtected Visual Environments (IMPROVE) data collected at monitoring locations across the United States during 1995 through 1999. The data show that the spatial pattern of a given chemical species’ contribution to the upper extremes of aerosol fine mass is often quite different than at lower fine mass concentrations. In some cases, the monitoring data suggest a casual relationship between specific aerosol source regions and the magnitude in which a species’ contribution to the upper extremes of fine mass is elevated above the contribution to median fine mass concentrations.     

Characterization of visibility impacts related to fine particulate matter in Canada

Canada has recently established standards for the management of particulate matter (PM) air quality. National networks currently measure PM mass concentrations and chemical speciation. Methods used in the U.S. IMPROVE network are applied to the 1994--2000 Canadian fine PM data to obtain a regional reconstruction of the visibility based on particle composition. Nationally, the greatest light extinction occurs in the Windsor-Quebec City corridor. Variations in the dominant chemical species responsible for the reduction in visibility are presented for regions across the country. In most regions, sulfate and nitrate contribute most greatly to reduced visibility. The visibility implications of achieving the Canada-Wide Standard (CWS) across the country are evaluated, with the greatest improvement in visibility associated with achieving the CWS in southern Ontario. Elsewhere in the country, achieving the CWS will actually result in deteriorating air quality. Improving current estimates of visibility requires higher spatially and temporally resolved measurements of organic and elemental carbon fractions and particulate nitrate.     

Assessing the Relative Contribution of Biogenic and Fossil Processes to Visibility-Scattering Aerosols Found in Remote Areas: Near-Term Organic Research Program

Abstract

Organic carbon has been found to be a significant component of aerosols that impair visibility in remote areas across the country. Organic aerosols are particularly important in western areas of the United States and contribute roughly equally with sulfate aerosols and dust in the total extinction budget. Potential visibility enhancement resulting from various future energy management options that reduce volatile organic carbon and particulate material emissions from fossil-energy-related processes hinges on the relative contribution of the fossil-fuel-derived organic component to the extinction budget. Thus, additional studies are needed to quantify the partitioning of organic carbon between biogenic and fossil sources. Relative humidity (RH) also plays an important role in visibility impairment. It is well known that water soluble aerosol species, such as sulfate and nitrate, can increase light-scattering efficiencies of fine particles by more than an order of magnitude as RH is increased from 20-30% to 90-95%. Organic carbon aerosol has been found to be a mixture of more soluble and less soluble components, but few studies have been performed to evaluate the RH response function of aerosols composed of these components, either separately or in combination, especially at high relative humidities. The purpose of this paper is to describe some experiments that could address the major uncertainties of biogenic and fossil carbon contributions to the fine particle extinction budget and visibility impairment.     

A Critical Assessment of Atmospheric Visibility and Aerosol Measurements in the Eastern United States

As part of a study examining the technical basis for a secondary national ambient air quality standard for fine particulate matter to protect visibility, we reviewed available data on atmospheric aerosol and visibility in the eastern U.S. This paper presents the results of that visibility and aerosol characterization.

Analysis of airport visibility data indicates that the annual median visual ranges in the East are in the 16-25 km range. In the absence of a "reference method," limited measurements of visibility using various types of instruments provide data generally in agreement with the airport visibility estimates when a contrast threshold of 0.05 is assumed in calculating visual range from the instrumental measurements.

Both long- and short-term aerosol measurements have yielded consistent results; however, because of the differences in instrumentation and laboratory analytical techniques among various studies, data often are not directly comparable. The measured annual average fine particulate matter mass concentration is about 18 μg/m³ in the rural East; during summer it increases to about 23 μg/m³. If all the sulfur in the fine mass is assumed to exist as ammonium sulfate, it would constitute 46 percent of the annual mean and about 60 percent of the summer mean fine mass concentrations. Carbon and volatiles, including water, are believed to constitute significant fractions of the fine mass; however, there are little data quantifying their contributions to fine mass and visibility impairment. Additional long-term measurements of visibility and fine aerosol and its various components are necessary to completely characterize visibility and aerosol in the East.     

济南市大气水平能见度与环境污染相关性分析

利用济南市2011年1月1日至12月31日大气水平能见度在线监测小时数据和对应细颗粒物(PM2.5)、PM2.5中碳组分(EC和OC)、挥发性有机物(VOC)及气象参数资料,分析污染物、气象参数等对能见度的影响。结果显示,相对湿度和PM2.5是影响能见度的主要因子,能见度与相对湿度及PM2.5浓度主要呈指对数关系。结合相对湿度条件对PM2.5浓度与能见度关系进行综合分析,得到相关经验模型公式,并利用2010年6月1日至11月30日的相应数据资料进行实例关系验证,结果表明,建立的经验模型公式有较好的实际应用价值。     

Regional Photochemical Measurement and Modeling Studies: A Summary of the Air & Waste Management Association International Specialty Conference

Abstract

This paper summarizes the Air & Waste Management Association’s International Specialty Conference, "Regional Photochemical Measurement and Modeling Studies," held in San Diego, California, on November 8-12,1993. The purpose of the conference was to facilitate exchange of information and to initiate better communication and interaction among scientists, air quality managers, regulators, and others involved in or applying tools (models and measurements to support the modeling efforts) that can be used to develop equitable and effective emissions management practices for attainment of ozone standards. Attendees heard more than 350 presentations from authors representing nearly 30 air quality and meteorological measurement and modeling studies from 18 countries. While the primary emphasis of the conference was technical, two policy sessions were included (Plenary and Concluding Sessions) to place the technical results in perspective with the policy issues. The technical agenda was divided into three subjects: Analysis of Field Measurements (results and interpretation), Modeling (status and results), and Other Topics. Papers presented at the conference are being published in a variety of journals or books to meet the needs of the scientific and policy communities. A complete bibliographical listing of the papers presented at the conference is included with this paper.

An unexpected outcome of the conference has been the development of an initiative for continuing the intercomparison of goals and scientific findings from regional air quality studies in Europe and North America, entitled “Regional Oxidants Programs Intercomparison” (ROxPIn). This paper will also discuss the goals and objectives of ROxPIn.     

DAQM-Simulated Spatial and Temporal Differences Among Visibility,PM, and Other Air Quality Concerns Under Realistic Emission Change Scenarios

The Denver Air Quality Modeling Study (DAQMS) is a comprehensive modeling effort originally undertaken to apportion sources of visibility degradation and examine the visibility benefits of future emission strategies in the Denver metropolitan area. Because of the detailed treatment of the chemical and physical processes and high temporal, vertical, and horizontal resolution of the system, it is possible to examine other air-related issues and their relationships to visibility. The DAQMS analysis system consists of the Denver Air Quality Model (DAQM), a three-dimensional Eulerian chemical-transport model including aerosol and gas-phase transport and transformation processes, a three-dimensional mesoscale meteorological modeling system, visibility analysis procedures, and an emissions processing system. DAQM, the meteorological model, and the emissions information operate on a domain covering approximately the entire state of Colorado with 8-km grid resolution and 15 vertical levels from the surface to the stratosphere. Analysis from a winter visibility episode illustrates the differences between spatial and temporal distributions of light extinction, fine and coarse particle aerosol concentrations, oxidants, and carbon monoxide under various emission scenarios. Studies aimed at exploring interrelationships between these air quality concerns for different seasons, meteorological conditions, and emission management scenarios are outlined.     

APCA Financial Statements for FY 1979-80

The U.S. Environmental Protection Agency (EPA) has proposed a new secondary standard based on visibility in urban areas. The proposed standard will be based on light extinction, calculated from 24-hr averaged measurements. It would be desirable to base the standard on a shorter averaging time to better represent human perception of visibility. This could be accomplished by either an estimation of extinction from semicontinuous particulate matter (PM) data or direct measurement of scattering and absorption. To this end we have compared 1-hr measurements of fine plus coarse particulate scattering using a nephelometer, along with an estimate of absorption from aethalometer measurements. The study took place in Lindon, UT, during February and March 2012. The nephelometer measurements were corrected for coarse particle scattering and compared to the Filter Dynamic Measurement System (FDMS) tapered element oscillating microbalance monitor (TEOM) PM_2.5 measurements. The two measurements agreed with a mass scattering coefficient of 3.3 ± 0.3 m²/g at relative humidity below 80%. However, at higher humidity, the nephelometer gave higher scattering results due to water absorbed by ammonium nitrate and ammonium sulfate in the particles. This particle-associated water is not measured by the FDMS TEOM. The FDMS TEOM data could be corrected for this difference using appropriate IMPROVE protocols if the particle composition is known. However, a better approach may be to use a particle measurement system that allows for semicontinuous measurements but also measures particle bound water. Data are presented from a 2003 study in Rubidoux, CA, showing how this could be accomplished using a Grimm model 1100 aerosol spectrometer or comparable instrument.

Implications: Visibility is currently based on 24-hr averaged PM mass and composition. A metric that captures diurnal changes would better represent human perception. Furthermore, if the PM measurement included aerosol bound water, this would negate the need to know particulate composition and relative humidity (RH), which is currently used to estimate visibility. Methods are outlined that could accomplish both of these objectives based on use of a PM monitor that includes aerosol-bound water. It is recommended that these techniques, coupled with appropriate measurements of light scattering and absorption by aerosols, be evaluated for potential use in the visibility based secondary standard.     

Comparisons of aerosol properties measured by impactors and light scattering from individual particles: refractive index,number and volume concentrations,and size distributions

The southeastern aerosol and visibility study (SEAVS) was conducted in Great Smoky Mountains National Park in summer 1995 to investigate variations in ambient aerosol size distributions and their effect on visibility. In this paper, we compare dry aerosol size distribution parameters from a MOUDI impactor and two different optical particle counters (OPCs). Size distributions from the various instruments are expressed in a common measure of size, specifically, optical and aerodynamic diameters are converted to a dry, geometric diameter basis. Comparisons of the real part of particle refractive index obtained directly from light scattering measurements and inferred from aerosol composition measurements are also shown. Real refractive indices from direct measurements and those computed from measured fine aerosol chemical composition were generally within ±0.02. Maximum differences in estimated accumulation mode integrated volume concentrations from all instruments were within ∼22%. Accumulation mode integrated number concentrations and geometric standard deviations from the two OPCs agreed within ∼30% and ∼3%, respectively. Differences between MOUDI- and OPC-derived accumulation mode number concentrations and geometric standard deviations were ∼20% and ∼8%, respectively. The average geometric volume mean diameters derived from the three instruments agreed within 15% or less. The volume median diameters obtained by fitting the CSU number concentration data to a lognormal function were typically the smallest. We show that these discrepancies can be related to the differences and biases in the measurement and data analysis techniques.     

The midlatitude North American background aerosol and global aerosol variation

Protocols for the particulate matter (PM) National Ambient Air Quality Standards (NAAQS), and the Regional Haze Rule (RHR) give two complementary definitions for "natural" background airborne particle concentrations in the United States. The definition for the NAAQS derives largely from reported annual averages, whereas the definition for the RHR takes into account the frequency of occurrence of a range of visibility conditions estimated using fine particle composition. These definitions are simple, static representations of background or "unmanageable" aerosol conditions in the United States. An accumulation of data from rural-remote sites representing global conditions indicates that the airborne particle concentrations are highly variable. Observational campaigns show weather-related variations, including incidents of regional or intercontinental transport of pollution that influence background aerosol levels over midlatitude North America. Defining a background in North America based on long-term observations relies mainly on the remote-rural IMPROVE network in the United States, with a few additional measurements from Canada. Examination of the frequency of occurrence of mass concentrations and particle components provides insight not only about annual median conditions but also the variability of apparent background conditions. The results of this analysis suggest that a more elaborate approach to defining an unmanageable background could improve the present approach taken for information input into the U.S. regulatory process. An approach interpreting the continental gradients in fine PM (PM2.5) concentrations and composition may be warranted.     

A Technical Amplification of NAPAP’s Findings

In September 1987, NAPAP released a 4-volume, 925 page interim report that summarized the effects of acidic precipitation on crops, forests, aquatic ecosystems, visibility, and human health. Following the release of the report, APCA coordinated an international conference to provide a forum for the technical amplification of the conclusions reached in NAPAP's report. Scientists from the United States and Canada were invited to participate in the conference. The focus of the meeting was concerned only with the technical aspects of the NAPAP report. At the conference, there were important research concepts presented that may require further attention before definitive, bottom line statements can be made concerning the effects of acid precipitation on the environment. The purpose of this paper is to summarize the key technical points made at the conference and provide NAPAP with additional scientific inputs as it begins to prepare for its 1990 Final Assessment Report.     

Effect of coal-fired power generation on visibility in a nearby national park

The Mohave coal-fired power plant has long been considered a major contributor to visibility impairment in Grand Canyon National Park. The permanent closure of the plant in 2005 provides the opportunity to test this assertion. Although this analysis, based on data from the Interagency Monitoring of Protected Environments (IMPROVE) Aerosol Network, shows that fine sulfate levels in the park dropped following the closure, no statistically significant improvement in visibility resulted. Difference-in-differences estimation was used to control for other influences. This finding has important implications for the methods generally employed to attribute visibility reductions to air pollution sources.     

Integrated assessment modeling of atmospheric pollutants in the Southern Appalachian Mountains: Part II. Fine particulate matter and visibility

As part of the Southern Appalachian Mountains Initiative, a comprehensive air quality modeling system was developed to evaluate potential emission control strategies to reduce atmospheric pollutant levels at the Class I areas located in the Southern Appalachian Mountains. Six multiday episodes between 1991 and 1995 were simulated, and the skill of the modeling system was evaluated. Two papers comprise various parts of this study. Part I details the ozone model performance and the methodology that was used to scale discrete episodic pollutant levels to seasonal and annual averages. This paper (part II) addresses issues involved with modeling particulate matter (PM) and its relationship to visibility. For most of the episodes, the fractional error was approximately 50% or less for the major constituents of the fine PM (i.e., sulfate [SO4] and organics) in the region. The mean normalized errors and fractional errors are generally larger for the NO3 and soil components, but these components are relatively small. Variations in modeling bias with pollutant levels were also examined. The model showed a systematic overestimation for low levels and an underestimation for high levels for most PM species. For ammonium, the model showed better performance at lower SO4 concentrations when the measured SO4 was assumed to be completely neutralized (ammonium sulfate) and better performance at higher SO4 concentrations when the partially neutralized (ammonium bisulfate) assumption was made. The contributions of various components of PM to reductions in visibility were also calculated; SO4 was found to be the major contributor.     

The Location of Maximum Exposure Due to An Instantaneous Release from a Point Source

An international specialty conference, jointly sponsored by the Air &; Waste Management Association (A&;WMA) and the U.S. Environmental Protection Agency (EPA), entitled “PM₁₀ Standards and Nontraditional Particulate Source Controls,” was held in Scottsdale, Arizona, January 12-15, 1992. The conference included 92 presentations in 17 technical sessions. Eighty-one peer-reviewed technical papers, two keynote addresses and one panel session summary describing novel applications, measurement processes, modeling techniques and control measures for nontraditional pollution sources are assembled in the Transactions¹. The technical issues addressed during the conference included: (1) measurement methods and data bases; (2) emissions source characterization; (3) source apportionment of nontraditional sources; (4) fugitive dust characterization and control technologies; (5) vegetative burning characterization and control technologies; (6) sources and controls of secondary aerosol and motor vehicle precursors; and (7) regulatory policies and State Implementation Plan (SIP) development. This paper gives an overview of the technical program     

上海市霾污染判别指标体系初步研究

随着全球变暖及工业污染排放的蔓延式发展,由空气污染带来的区域能见度恶化越来越成为中国东部经济发达地区所面临的严重区域性问题,常出现大范围的雾霾天气,造成区域空气质量的恶化及能见度水平的下降.基于对能见度及相对湿度、颗粒物浓度和组分的观测分析及影响能见度的相对湿度和空气污染因子的理论分析,提出了环保范畴内的霾污染概念,并制定了包括能见度、颗粒物浓度及其组分的上海市霾污染判别指标体系,基于颗粒物组分观测数据,对相对湿度因子进行了参数化.根据所提出的指标体系,通过上海市某点位一年观测数据的跟踪分析发现,根据霾污染判别指标体系计算得到的霾污染天数与气象学意义上的霾天数具有很好的对应关系,且新的判别指标体系能很好地区分霾污染和浮尘过程.     

Relationships between Aerosol Extinction Coefficients Derived from Airport Visual Range Observations and Alternative Measures of Airborne Particle Mass

Epidemiological assessments of population exposures to airborne particles are often hampered by the scarcity of available fine particle mass measurements. In an attempt to overcome this serious problem, we analyze In this paper methods for predicting fine particle (M ₁) and Inhalable particle (IP) mass concentrations using relative humidity corrected light extinction coefficient (b _ext) estimated from airport visual range (V _r) observations. The analyses presented are based on theoretical determinations as well as statistical investigations utilizing EPA's NASN and Inhalable Particle Monitoring Network (IPMN) data bases and routine airport visual range observations In twelve large U.S. cities. Our results Indicate that, after controlling for certain limitations of airport visual range data, most of the regression models developed in this paper can be applied satisfactorily to predict M _t and IP. Furthermore, our findings Indicate that a more representative formula than the commonly used meteorological range formula to predict atmospheric b _ext values in urban areas may be b _ext = (1.8 ± 0.04)/V _r. Because of known local or regional influences, however, we do suggest calibration of any predictive model which utilizes airport visibility data against site-specific aerometric data on particle mass concentrations or scattering coefficient measurements.