Long-term records of condensed-phase chemical data are presented from the Adirondack Mountain region of northern New York, USA. These data records are particularly valuable due to the combinations of aerosol, cloud, and precipitation measurements. Objectives of the research and this overview paper include the evaluation of emission reductions of regulated air pollutants and the observed effects on measured deposition, as well as the implications of changing pollutant concentration levels on human health and climate. Summer season cloud chemistry and year-round wet deposition and particulate matter data from two stations on Whiteface Mountain are presented to highlight some of the research and monitoring activities at this mountain location. Clear decreases in the anion concentrations and increases in pH over the past two decades have been observed in cloud and precipitation results. Large decreases in aerosol sulfate (> 80%) and aerosol optical black carbon (> 60%) have been observed for these species over the nearly 40 year summit observatory data record for these measurements, and decreases in PM 2.5 mass, sulfate, nitrate, and ammonium have also been recorded over the shorter 15 year period of measurement at the Marble Mountain Lodge level. The studies cited here highlight some of the past successes of air pollution regulation under the Clean Air Act and Amendments and pave the way for future progress in reducing air pollution.
Whiteface Mountain, with an elevation of 1483 m above sea level, is a relatively low mountain by global standards. At the same time, the summit is some 90 m above the tree line and it is the fifth highest peak in the Adirondack Mountain Range of New York State. Whiteface Mountain is set apart from the other Adirondack High Peaks, providing an ideal location for many types of atmospheric measurements. The geographical location in the northeastern U.S., the lone massif character of the mountain, and the fact that the summit is very often enveloped in cloud has made the observatory an attractive place for scientific research. A four story building specifically for the purposes of scientific research and fire monitoring was built on the summit in 1971. The headquarters of the Whiteface Mountain facility, the Marble Mountain Lodge, is perched on the shoulder of the massif at an elevation of 604 m a.s.l. In some cases the same measurements are made at the two locations to explore the two different but geographically close environments. A summary of past and current measurement activity at both locations is presented in the paper along with selected examples of data sets, analyses, and applications. Important research in the areas of forest ecology, cloud water chemistry, precipitation chemistry, reactive trace gases, and airborne particulate matter are reviewed. Collected data sets for temperature and ozone at the summit are presented, as well as research linking the measured gaseous SO 2 to acid deposition at this location. In addition, an example is given using this long-term data for both gases and particulate matter that helps to establish the accountability of air pollution regulations in the control of sulfur oxides.
Measurements of ozone and reactive trace gases spanning four decades at the Whiteface Mountain summit observatory are presented. Ozone (O 3 ) measurements began in the mid-1970's, and acid rain and O 3 precursor gas measurements became routine in the late 1980's and early 1990's. Measurements at the lower altitude lodge level have also been performed routinely since about 2000. The 40-year O 3 record shows up and down fluctuations through the 1980's, a relatively stable period into the early 2000's, and indications of a decreasing trend over the past ten years. Sulfur dioxide (SO 2 ) and carbon monoxide (CO) trends are clearly decreasing over the roughly 25-year period of measurements at the summit observatory. Oxides of nitrogen (NO y and NO 2 ) show rather more complicated trends, increasing to a maximum in the mid-2000's, and decreasing sharply until 2011 with slight increases in concentration since then. Wind rose analysis shows the greatest contribution to high concentrations of precursor gases are from the west, southwest, and southern sectors, with SO 2 and oxides of nitrogen having the most sharply defined high pollution sectors. Seasonal variations of trace gas concentrations at the summit and lodge levels are also examined. Ozone concentrations are highest in the spring months at both locations, and higher at the summit than the lodge. In contrast precursor gases (SO 2 and NO x ) show highest concentrations in winter months with the lodge consistently higher than the summit.
Aqueous chemical processing within cloud and fog water is thought to be a key process in the production and transformation of secondary organic aerosol mass, found abundantly and ubiquitously throughout the troposphere. Yet, significant uncertainty remains regarding the organic chemical reactions taking place within clouds and the conditions under which those reactions occur, owing to the wide variety of organic compounds and their evolution under highly variable conditions when cycled through clouds. Continuous observations from a fixed remote site like Whiteface Mountain (WFM) in New York State and other mountaintop sites have been used to unravel complex multi-phase interactions in the past, particularly the conversion of gas-phase emissions of SO2 to sulfuric acid within cloud droplets in the presence of sunlight. These scientific insights led to successful control strategies that reduced aerosol sulfate and cloud water acidity substantially over the following decades. This paper provides an overview of observations obtained during a pilot study that took place at WFM in August 2017 aimed at obtaining a better understanding of Chemical Processing of Organic compounds within Clouds (CPOC). During the CPOC pilot study, aerosol cloud activation efficiency, particle size distribution and chemical composition measurements were obtained below-cloud for comparison to routine observations at WFM including cloud water composition and reactive trace gases. Additional instruments deployed for the CPOC pilot study included a doppler LiDAR, sun photometer and radiosondes, to assist in evaluating the meteorological context for the below-cloud and summit observations.
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