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A synoptic climatological analysis of winter visibility trends in the mideastern United States

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Long-term trends in wintertime visibility are examined in eight mideastern U.S. cities in light of the underlying climatology. Using an array of meteorological elements known to be related to visibility, a synoptic climatological classification is developed, producing a baseline climate for each city. This approach allows for an analysis of long-term air quality trends which are unrelated climatic variations.Yearly mean visibility levels are closely related to climatic variations. Years with frequent occurrences of continental polar and arctic air masses and cold front passages exhibit high visibility, while low air quality is related to overrunning situations (a warm or stationary front to the south) and the advection of Atlantic maritime polar air. Winter air quality declined from the early 1950s to 1970, improved throughout the mid 1970s, and either remained steady or improved slightly thereafter.
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... Visibility represents one of the dominant features of the climate and landscape of an area. Although it is highly affected by atmospheric circulation and the prevailing meteorological conditions, under clear sky conditions it is mainly determined by the loading in atmospheric aerosols (Davis, 1991;Lee, 1994;van Beelen and van Delden, 2012;Doyle and Dorling, 2002;Singh and Dey, 2012); therefore, visibility can be considered as a strong indicator of air quality over an area. Horizontal visibility has also been introduced in formulas for the estimation of atmospheric turbidity parameters (e.g., in the Ångström atmospheric turbidity coefficients; Eltbaakh et al., 2012). ...
... Although the use of visibility as a viable atmospheric variable has been disputed by many researchers due to the numerous biases related to observational procedures (Davis, 1991), visibility statistics have been increasingly used as a surrogate for aerosol load (Zhao et al., 2011), especially since visibility records span quite long-term periods. Today, there is a large number of studies that use visibility observations to investigate the spatial and temporal variation of the optical properties of the atmosphere, mainly in relation to pollutant emissions and aerosol load. ...
... Urban environments are of particular interest, as air pollution from local sources is superimposed on regional ones, strongly impacting visibility (Davis, 1991;Eidels-Dubovoi, 2002;Tsai et al., 2003Tsai et al., , 2007Dayan and Levy, 2005;Chang et al., 2009;Kim, 2015). ...
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... Two-stage clustering i.e. average linkage followed by k-means was the preferred approach, since it showed to have the best performance in terms of cluster cohesion. Furthermore, it was successfully applied in previous studies (Davis, 1991;Davis and Walker, 1992;Davis and Gay, 1993) that have aimed to link air pollution and air quality with meteorology. Average linkage clustering was employed by Cheng et al. (1992) to investigate pollution concentrations O 3 and total suspended particles (TSP)) in Philadelphia during the summer season. ...
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... Consequently, visibility 47 tends to decrease when air pollutant emissions increase, whereas it is the highest within non-48 polluted, pristine atmospheres (Sloane, 1982). Visibility is also influenced by meteorological 49 conditions, both in terms of local weather conditions and synoptic weather patterns (Davis, 1991;50 Sloane, 1983; Van Beelen and Van Delden, 2012), as they can limit or enhance the transport and 51 dispersion of atmospheric aerosols (Founda et al., 2016). Moreover, they influence the aerosol 52 sources and sinks: for example, wind speed promotes the re-suspension of dust particles, 53 temperature and solar radiation trigger photochemistry and favour the production of secondary 54 aerosols, while relative humidity influences aerosols size distribution (Van Beelen and Van Delden, 55 2012) through hygroscopic growth (Singh et al., 2017) and thus particle ability to diffuse visible 56 light. ...
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... The TSI is advantageous in that sub-daily meteorological observations taken at a single observation station can provide a robust indication of the synoptic-scale atmospheric environment over a sub-continental region, without the need for upper air observations or multiple surface stations (Kalkstein and Corrigan, 1986). The procedure has been successfully used in a variety of climatological and meteorological applications including long-term climatic change (Kalkstein et al., 1990), aerosol variability and ozone pollution (Kalkstein and Corrigan, 1986;Davis, 1991;Brodie et al., 2017), and snowfall and snow ablation variability Leathers and Ellis, 1996;Karmosky, 2007;Suriano, 2018, among others). While similar procedures, such as self-organizing maps, may have produced viable results, the TSI is a time-tested procedure for classifying synoptic-scale environments. ...
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