Spatial and monthly trends in speciated fine particle concentration in the United States

Abstract

In the spring of 1985 an interagency consortium of federal land management agencies and the Environmental Protection Agency established the Interagency Monitoring of Protected Visual Environments (IMPROVE) network to assess visibility and aerosol monitoring for the purpose of tracking spatial and temporal trends of visibility and visibility‐impairing particles in rural areas. The program was initiated with 20 monitoring sites and was expanded to 165 sites between 2000 and 2003. This paper reports on fine aerosol data collected in the year 2001 at 143 sites. The major fine (dp < 2.5 μm) particle aerosol species, sulfates, nitrates, organics, light‐absorbing carbon, and wind‐blown dust, and coarse gravimetric mass are monitored, and at some sites, light scattering and/or extinction are measured. Sulfates, carbon, and crustal material are responsible for most of the fine mass at the majority of locations throughout the United States, while at sites in southern California and the midwestern United States, nitrates can contribute significantly. In the eastern United States, sulfates contribute between 50 and 60% of the fine mass. Sulfate concentrations tend to be highest in the summer months while organic concentrations can be high in the spring, summer, or fall seasons, depending upon fire‐related emissions. However, at the two urban sites, Phoenix, Arizona, and Puget Sound, Washington, organics peak during the winter months. Nitrate concentrations also tend to be highest during the winter months. During the spring months in many areas of the western United States, fine soil can contribute as much as 40% of fine mass. The temporal changes in soil concentration that occur simultaneously over much of the western United States including the Rocky Mountain region suggest a large source region, possibly long‐range transport of Asian dust.

Long-term dust climatology in the western United States reconstructed from routine aerosol ground monitoring

“…Outside the deserts, there are two sites in Colorado where previous model studies have found that high wind power in spring lifts surface soil grains (Gillette and Hansen, 1989). Overall, the spatial distribution is similar to the dust source map reported in previous studies (Malm et al, 2004;Kavouras et al, 2007).…”

“…This subset of IMPROVE sites, deployed in eight western states (Fig. 1), is chosen based on the findings in previous studies that have identified the geographical distribution of active dust sources in the North America (Gillette and Passi, 1988;Malm et al, 2004;Van Curen, et al, 2002;Wells et al, 2007;Draxler et al, 2010). These regions are generally associated with high wind power over barren land.…”

Effect of power plant emission reductions on a nearby wilderness area: a case study in northwestern Colorado

“…The nephelometer at Buffalo Pass measures particle light scattering which is caused by both fine and coarse aerosol species and is the largest contributor to haze in most locations (Malm et al 2004). Data are available from the IMPROVE website as an hourly average aerosol scattering coefficient (B sp ) reported in megameter.…”

“…The composition of fine aerosols at MOZI1 is dominated by sulfates, organic carbon, and soil components, which make up on average 30 %, 38 %, and 22 %, respectively, of the fine particle mass. In western USA, sulfates largely are a product of power plant SO 2 emissions, organic aerosols are associated with wildfire activity, and the soil component reflects wind-blown dust (Malm et al 2004). Table 2 shows annual average aerosol concentrations for sulfate and nitrate and the haze index (deciview) in the before and after periods for the 20 % clearest, 20 % haziest days, and for all days.…”

“…Although the wilderness is in a remote part of the state, its western boundary is withinthe State of Colorado that sulfur dioxide (SO 2 ) and nitrogen oxide (NOx) emissions from Hayden and Craig were contributing to visibility impairment in the wilderness (Colorado Department of Public Health and Environment 2007). Sulfate aerosols formed in the atmosphere from gaseous SO 2 often are the largest single contributor to visibility impairment (Malm et al 2004). In 1994, the Mount Zirkel Visibility Study was commissioned to determine the cause of visibility impairment in the MZWA (Watson et al 1996).…”