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.     

Sources of Fine Particulate Species in Ambient Air over Lake Champlain Basin,VT

Abstract

This study is a part of an ongoing investigation of the types and locations of emission sources that contribute fine particulate air contaminants to Underhill, VT. The air quality monitoring data used for this study are from the Interagency Monitoring of Protected Visual Environments network for the period of 2001–2003 for the Underhill site. The main source-receptor modeling techniques used are the positive matrix factorization (PMF) and potential source contribution function (PSCF). This new study is intended as a comparison to a previous study of the 1988–1995 Underhill data that successfully revealed a total of 11 types of emission sources with significant contributions to this rural site. This new study has identified a total of nine sources: nitrate-rich secondary aerosol, wood smoke, East Coast oil combustion, automobile emission, metal working, soil/dust, sulfur-rich aerosol type I, sulfur-rich aerosol type II, and sea salt/road salt. Furthermore, the mass contributions from the PMF identified sources that correspond with sampling days with either good or poor visibility were analyzed to seek possible correlations. It has been shown that sulfur-rich aerosol type I, nitrate aerosol, and automobile emission are the most important contributors to visibility degradation. Soil/dust and sea salt/road salt also have an added effect.     

Particulate Matter in California: Part 1—Intercomparison of Several PM2.5, PM10–2.5, and PM10 Monitoring Networks

Abstract

It will be many years before the recently deployed network of fine particulate matter with an aerodynamic diameter less than 2.5 [H9262]m (PM_2.5) Federal Reference Method (FRM) samplers produces information on nonattainment areas, trends, and source impacts. However, data on PM_2.5 and its major constituents have been routinely collected in California for the past 20 years. The California Air Resources Board operated as many as 20 dichotomous (dichot) samplers for PM_2.5 and coarse PM (PM_10–2.5). The California Acid Deposition Monitoring Program (CADMP) collected 12-h-average PM_2.5 and PM₁₀ from 1988 to 1995 at ten urban and rural sites and 24-h-average PM_2.5 at five urban sites since 1995. Beginning in 1994, the Children’s Health Study collected 2-week averages of PM_2.5 in 12 communities in southern California using the Two-Week Sampler (TWS). Comparisons of collocated samples establish relationships between the dichot, CADMP, and TWS samplers and the 82-site network of PM_2.5 FRM samplers deployed since 1999 in California. PM mass data from the different monitoring programs have modest to high correlation to FRM mass data, fairly small systematic biases and negative proportional biases ranging from 7 to 22%. If the biases are taken into account, all of the programs should be considered comparable with the FRM program. Thus, historical data can be used to develop long-term PM trends in California.     

The Sixty-Sixth Annual Meeting of the Air Pollution Control Association

Abstract

The U.S. Clean Air Act, amended in 1990, mandated the establishment of the Grand Canyon Visibility Transport Commission (GCVTC). The commission is required to submit a report to the U.S. Environmental Protection Agency addressing visibility issues in the region, including "the establishment of clean air corridors, in which additional restrictions on increases in emissions may be appropriate to protect visibility in affected Class I areas." This paper presents a methodology to identify candidate geographic areas for consideration for Clean Air Corridor (CAC) status for Colorado Plateau Class I areas. The methodology uses thousands of model determined trajectories over a five year period (1988 to 1992) to indicate the paths taken by air that arrives during clean air conditions at Class I areas. These clean air back-trajectories identify upwind areas where pollution emissions could jeopardize currently pristine visibility. Using this methodology, six candidate areas are identified, ranging in size from 75,000 to 506,000 square miles, and permitting varying levels of visibility protection for clean air days at Grand Canyon, Canyonlands, and Petrified Forest National Parks. Assuming effective emissions management of the CAC, the larger the CAC, the greater the visibility protection during clean air conditions.     

Ozone and Other Air Quality-Related Variables Affecting Visibility in the Southeast United States

Abstract

An analysis of ozone (O₃) concentrations and several other air quality-related variables was performed to elucidate their relationship with visibility at five urban and semi-urban locations in the southeast United States during the summer seasons of 1980-1996. The role and impact of O₃ on aerosols was investigated to ascertain a relationship with visibility. Regional trend analysis over the 1980s reveals an increase in maximum O₃ concentration coupled with a decrease in visibility. However, a similar analysis for the 1990s shows a leveling-off of both O₃ and visibility; in both cases, the results were not statistically significant at the 5% level. A case study of site-specific trends at Nashville, TN, followed similar trends. To better understand the relationships between O₃ concentration and visibility, the analysis was varied from yearly through daily to hourly averaged values. This increased temporal resolution showed a statistically significant inverse relationship between visibility and O₃. Site-specific hourly r² values ranged from 0.02 to 0.43. Additionally, by performing back-trajectory analysis, it was found that the visibility degraded by air mass migration over polluted areas.     

Analysis of PM10 Trends in the United States from 1988 through 1995

ABSTRACT

Because the U. S. Environmental Protection Agency (EPA) has changed the National Ambient Air Quality Standards (NAAQS) for ambient particulate matter (PM), there is a great deal of interest in determining recent PM trends. This paper examines trends in PM₁₀ (i.e., particulate matter less than 10 micrometers in diameter) for areas of the United States based on their attainment status—for PM₁₀ and ozone nonattainment and attainment areas. The analysis also focuses on urban, suburban, and rural areas, and eastern and western areas. The time period of evaluation is from 1988 through 1995. To shed further light on the ambient PM₁₀ trends, trends in ambient SO₂, NO₂, and volatile organic compounds (VOCs) are also analyzed. Finally, trends in emission inventories of SO₂, NO_x, VOCs, and PM₁₀ are evaluated. Results of the analysis show that widespread and similar reductions in PM₁₀ levels have occurred over the last seven years. Annual reductions range from 3.0% to 3.8%, with the greatest reductions coming in PM₁₀ nonattainment areas, but with very significant reductions also in PM₁₀ attainment areas, ozone attainment areas, and rural areas. The widespread reductions appear to be due to a set of controls or common factors that are having a fairly uniform effect in all of the areas. The consistency of the reductions in different areas suggests that the reductions may also be primarily in the fine particles (i.e., those less than 2.5 micrometers in diameter, or PM_2.5), which are more readily transported than coarse particles.     

Source apportionment of visibility degradation problems in Brisbane (Australia) using the multiple linear regression techniques

Different aspects of visibility degradation problems in Brisbane were investigated through concurrent visibility monitoring and aerosol sampling programs carried out in 1995. The relationship between the light extinction coefficients and aerosol mass/composition was derived by using multiple linear regression techniques. The visibility properties at different sites in Brisbane were found to be correlated with each other on a daily basis, but not correlated with each other hour by hour. The cause of scattering of light by moisture (b_sw) was due to sulphate particles which shift to a larger size under high-humidity conditions. The scattering of light by particulate matter (b_sp) was found to be highly correlated with the mass of fine aerosols, in particular the mass of fine soot, sulphate and non-soil K. For the period studied, on average, the total light extinction coefficient (b_ext) at five sites in Brisbane was 0.65×10⁻⁴ m⁻¹, considerably smaller than those values found in other Australian and overseas cities. On average, the major component of b_ext is b_sp (49% of b_ext), followed by b_ap (the absorption of light, mainly by fine soot particles, 28%), b_sg (Rayleigh scattering, 20%) and b_sw (3%). The absorption of light by NO₂ (b_ag) is expected to contribute less than 5% of b_ext. On average, the percentage contribution of the visibility degrading species to b_ext (excluding b_ag) were: soot (53%), sulphate (21%), Rayleigh scattering (20%), non-soil K (2%) and humidity (3%). In terms of visibility degrading sources, motor vehicles (including soot and the secondary products) are expected to contribute more than half of the b_ext (excluding b_ag) in Brisbane on average, followed by secondary sulphates (17%) and biomass burning (10%).     

Comparison of Selenium and Sulfur at Remote Sites

Abstract

The Interagency Monitoring of Protected Visual Environments (IMPROVE) particulate monitoring network has been collecting aerosols for visibility apportionment at remote sites in the United States since 1988. The measurements include the major PM_2.5 components, such as sulfur, carbon, and nitrate, and trace elements, such as selenium. This paper will examine the relationship between the sulfurs and selenium concentrations at 61 sites for samples collected in the seasonal year 1993. Maps of mean sulfur and selenium measurements in summer 1993 and winter 1993-1994 indicate that there are well-defined regional patterns for both elements, with concentrations in the Appalachian region that are ten times those in areas of the Pacific Northwest. The S/Se ratios of means are relatively uniform across the United States, at around 2000 in summer and 1000 in winter, indicating a strong sulfur-selenium relationship. The role of conversion of S0₂ to sulfate can also be deduced from the means. For individual samples taken during summer 1993, there is a high correlation between the two variables in the East, especially at sites in the Northeast, where the correlation coefficients (r²) are around 0.9. In the West, the correlation is much lower. This is attributed to fewer sources and differing emission factors.     

Eight-Hour Ozone Trends at Sites in Lake Michigan Ozone Nonattainment Areas

ABSTRACT

Temperature-adjusted trends in 1-hr and 8-hr ozone averages were calculated for ten sites near Lake Michigan for 1980-1995. Results show that ozone trends declined similarly according to both metrics for sites on the west side of the lake. This suggests that the factors underlying the trends were similar. These factors include, among others, ozone control programs designed to address the 1-hr standard. Thus, these control programs may have been similarly effective in moving these sites toward compliance with the 8-hr standard.     

Precipitation in Light Extinction Reconstruction

Abstract

The U.S. Environmental Protection Agency (EPA) published the Regional Haze Rule (RHR) in 1999.¹ The RHR default goal is to reduce haze linearly to natural background in 2064 from the baseline period of 2000–2004. The EPA default method^2,3 for estimating natural and baseline visibility uses the Interagency Monitoring of Protected Visual Environments (IMPROVE) formula. The IMPROVE formula predicts the light extinction coefficient from aerosol chemical concentrations measured by the IMPROVE network. The IMPROVE light scattering coefficient formula using data from 1994–2002 underestimated the measured light scattering coefficient by 700 Mm^?1, on average, on days with precipitation. Also, precipitation occurred as often on the clearest as haziest days. This led to estimating the light extinction coefficient of precipitation, averaged over all days, as the light scattering coefficient on days with precipitation (700 Mm^?1) multiplied by the percent of precipitation days in a year. This estimate added to the IMPROVE formula light extinction estimate gives a real world estimate of visibility for the 20% clearest, 20% haziest, and all days. For example, in 1993, the EPAs Report to Congress projected visibility in Class I areas would improve by 3 deciviews by 2010 across the haziest portions of the eastern United States because of the 1990 Clean Air Act Amendments. Omitted was the light extinction coefficient of precipitation. Adding in the estimated light extinction coefficient of precipitation, the estimated visibility improvement declines to <1 deci-view.     

Recommended metric for tracking visibility progress in the Regional Haze Rule

For many national parks and wilderness areas with special air quality protections (Class I areas) in the western United States (U.S.), wildfire smoke and dust events can have a large impact on visibility. The U.S. Environmental Protection Agency’s (EPA) 1999 Regional Haze Rule used the 20% haziest days to track visibility changes over time even if they are dominated by smoke or dust. Visibility on the 20% haziest days has remained constant or degraded over the last 16 yr at some Class I areas despite widespread emission reductions from anthropogenic sources. To better track visibility changes specifically associated with anthropogenic pollution sources rather than natural sources, the EPA has revised the Regional Haze Rule to track visibility on the 20% most anthropogenically impaired (hereafter, most impaired) days rather than the haziest days. To support the implementation of this revised requirement, the EPA has proposed (but not finalized) a recommended metric for characterizing the anthropogenic and natural portions of the daily extinction budget at each site. This metric selects the 20% most impaired days based on these portions using a “delta deciview” approach to quantify the deciview scale impact of anthropogenic light extinction. Using this metric, sulfate and nitrate make up the majority of the anthropogenic extinction in 2015 on these days, with natural extinction largely made up of organic carbon mass in the eastern U.S. and a combination of organic carbon mass, dust components, and sea salt in the western U.S. For sites in the western U.S., the seasonality of days selected as the 20% most impaired is different than the seasonality of the 20% haziest days, with many more winter and spring days selected. Applying this new metric to the 2000–2015 period across sites representing Class I areas results in substantial changes in the calculated visibility trend for the northern Rockies and southwest U.S., but little change for the eastern U.S.

Implications: Changing the approach for tracking visibility in the Regional Haze Rule allows the EPA, states, and the public to track visibility on days when reductions in anthropogenic emissions have the greatest potential to improve the view. The calculations involved with the recommended metric can be incorporated into the routine IMPROVE (Interagency Monitoring of Protected Visual Environments) data processing, enabling rapid analysis of current and future visibility trends. Natural visibility conditions are important in the calculations for the recommended metric, necessitating the need for additional analysis and potential refinement of their values.     

Effects of Aerosol Species on Atmospheric Visibility in Kaohsiung City,Taiwan

Abstract

Visibility data collected from Kaohsiung City, Taiwan, for the past two decades indicated that the air pollutants have significantly degraded visibility in recent years. During our study period, the seasonal mean visibilities in spring, summer, fall, and winter were only 5.4, 9.1, 8.2, and 3.4 km, respectively. To ascertain how urban aerosols influence the visibility, we conducted concurrent visibility monitoring and aerosol sampling in 1999 to identify the principal causes of visibility impairments in the region. In this study, ambient aerosols were sampled and analyzed for 11 constituents, including water-soluble ions and carbon materials, to investigate the chemical composition of Kaohsiung aerosols. Stepwise regression method was used to correlate the impact of aerosol species on visibility impairments. Both seasonal and diurnal variation patterns were found from the monitoring of visibility. Our results showed that light scattering was attributed primarily to aerosols with sizes that range from 0.26 to 0.90 μm, corresponding with the wavelength region of visible light, which accounted for ～72% of the light scattering coefficient. Sulfate was a dominant component that affected both the light scattering coefficient and the visibility in the region. On average, (NH₄)₂SO₄, NH₄NO₃, total carbon, and fine particulate matter (PM_2.5)-remainder contributed 53%, 17%, 16%, and 14% to total light scattering, respectively. An empirical regression model of visibility based on sulfate, elemental carbon, and humidity was developed, and the comparison indicated that visibility in an urban area could be properly simulated by the equation derived herein.     

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.     

U.S. National PM2.5 Chemical Speciation Monitoring Networks—CSN and IMPROVE: Description of networks

The U.S. Environmental Protection Agency (EPA) initiated the national PM_2.5 Chemical Speciation Monitoring Network (CSN) in 2000 to support evaluation of long-term trends and to better quantify the impact of sources on particulate matter (PM) concentrations in the size range below 2.5 μm aerodynamic diameter (PM_2.5; fine particles). The network peaked at more than 260 sites in 2005. In response to the 1999 Regional Haze Rule and the need to better understand the regional transport of PM, EPA also augmented the long-existing Interagency Monitoring of Protected Visual Environments (IMPROVE) visibility monitoring network in 2000, adding nearly 100 additional IMPROVE sites in rural Class 1 Areas across the country. Both networks measure the major chemical components of PM_2.5 using historically accepted filter-based methods. Components measured by both networks include major anions, carbonaceous material, and a series of trace elements. CSN also measures ammonium and other cations directly, whereas IMPROVE estimates ammonium assuming complete neutralization of the measured sulfate and nitrate. IMPROVE also measures chloride and nitrite. In general, the field and laboratory approaches used in the two networks are similar; however, there are numerous, often subtle differences in sampling and chemical analysis methods, shipping, and quality control practices. These could potentially affect merging the two data sets when used to understand better the impact of sources on PM concentrations and the regional nature and long-range transport of PM_2.5. This paper describes, for the first time in the peer-reviewed literature, these networks as they have existed since 2000, outlines differences in field and laboratory approaches, provides a summary of the analytical parameters that address data uncertainty, and summarizes major network changes since the inception of CSN.

ImplicationsTwo long-term chemical speciation particle monitoring networks have operated simultaneously in the United States since 2001, when the EPA began regular operations of its PM_2.5 Chemical Speciation Monitoring Network (IMPROVE began in 1988). These networks use similar field sampling and analytical methods, but there are numerous, often subtle differences in equipment and methodologies that can affect the results. This paper describes these networks since 2000 (inception of CSN) and their differences, and summarizes the analytical parameters that address data uncertainty, providing researchers and policymakers with background information they may need (e.g., for 2018 PM_2.5 designation and State Implementation Plan process; McCarthy, 2013) to assess results from each network and decide how these data sets can be mutually employed for enhanced analyses. Changes in CSN and IMPROVE that have occurred over the years also are described.     

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.     

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.     

Visibility Trends in Korea during the Past Two Decades

Abstract

Temporal trends and spatial distributions of visibility measured by the human eye over 60 stations in Korea between 1980 and 2000 are analyzed and discussed. Generally, visibility is lowest on winter mornings and highest on summer afternoons throughout Korea. Visibility in Seoul is now in an increasing trend while it has decreased nationwide, especially in clean coastal areas. Spatial distribution of visibility in the 1990s was related negatively to that of relative humidity (RH). However, visibility generally decreased despite an overall decrease in RH throughout the country. Air pollutants should have played a role in this dissonant variation, particularly in relatively clean areas and on summer afternoons. It was interpreted that the visibility increase in major metropolitan areas, including the greater Seoul area, in the 1990s was caused mainly by the reduction in pollutant emissions by rigorous government policy. But the effect of the emission reduction was manifested with decreasing RH.     

Identification of Sources Contributing to Mid-Atlantic Regional Aerosol

Abstract

Source types or source regions contributing to the concentration of atmospheric fine particles measured at Brigantine National Wildlife Refuge, NJ, were identified using a factor analysis model called Positive Matrix Factorization (PMF). Cluster analysis of backward air trajectories on days of high- and low-factor concentrations was used to link factors to potential source regions. Brigantine is a Class I visibility area with few local sources in the center of the eastern urban corridor and is therefore a good location to study Mid-Atlantic regional aerosol. Sulfate (expressed as ammonium sulfate) was the most abundant species, accounting for 49% of annual average fine mass. Organic compounds (22%; expressed as 1.4 × organic carbon) and ammonium nitrate (10%) were the next abundant species. Some evidence herein suggests that secondary organic aerosol formation is an important contributor to summertime regional aerosol.

Nine factors were identified that contributed to PM_2.5 mass concentrations: coal combustion factors (66%, summer and winter), sea salt factors (9%, fresh and aged), motor vehicle/mixed combustion (8%), diesel/Zn-Pb (6%), incinerator/industrial (5%), oil combustion (4%), and soil (2%). The aged sea salt concentrations were highest in springtime, when the land breeze-sea breeze cycle is strongest. Comparison of backward air trajectories of high- and low-concentration days suggests that Brigantine is surrounded by sources of oil combustion, motor vehicle/mixed combustion, and waste incinerator/industrial emissions that together account for 17% of PM_2.5 mass. The diesel/Zn-Pb factor was associated with sources north and west of Brigantine. Coal combustion factors were associated with coal-fired power plants west and southwest of the site. Particulate carbon was associated not only with oil combustion, motor vehicle/mixed combustion, waste incinerator/industrial, and diesel/Pb-Zn, but also with the coal combustion factors, perhaps through common transport.     

Examining Impacts of Visibility and PM Strategies before Implementation

ABSTRACT

One of the major challenges facing the world today is defining paths to sustainable futures. Part of the challenge is developing a national energy strategy that promotes an adequate energy supply for the United States, while enhancing environmental quality and maintaining U.S. competitiveness in the world economy. To assist in this challenge, we have developed a screening technique to analyze the effectiveness of different proposed emissions reduction strategies. The technique, referred to as the visibility assessment screening technique (VAST), is designed to examine possible impacts on visibility of emission changes of sulfur oxides, nitrogen oxides, volatile organic compounds (i.e., SO₂, NO_x, and VOC) and fine and coarse particulate matter (PM). The influence of relative humidity, natural aerosols, and the chemical interconnections among sulfur and nitrogen components of aerosols in determining the effectiveness of Clean Air Act Amendment and other projected energy-related emissions changes on eastern and western visibility are explored.

The effectiveness of these strategies on particulate matter impacts and potentially on ozone is also noted.     

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。