PROPHET 1998 meteorological overview and air‐mass classification

Abstract

Abstract. The Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET) summer 1998 measurements intensive was conducted from a tower above a forested site in northern Michigan. This paper provides a brief overview of the meteorological conditions and establishes that the study period was moderately drier and warmer than the climatological mean. The paper also identifies and chemically characterizes the major air mass types influencing the site. Meteorological analyses and back trajectories establish that air mass origin oscillated between relatively clean Canadian regions (except for periods influenced by Canadian forest fires) and regions of greater anthropogenic emissions in the contiguous United States. Higher mixing ratios of ozone, CO, NO•, and NO• were generally associated with southerly transport, which occurred 24% of the time. Lower mixing ratios were observed under northerly transport, which occurred 44% of the time. The dominance of northerly transport was due to a stronger than normal Hudson Bay low. The remaining 32% of the time was occupied by transitional periods between distinct air masses. A positive slope exists between ozone and CO when photochemically aged air masses are selected. However, no meaningful relationship between ozone and CO was observed when northerly and southerly transport periods were considered separately. Comparison to other summertime rural locations suggests that rapid and frequent transitions between air masses of contrasting source regions play an important role in maintaining the 0.3 O3/CO slope commonly observed in eastern North America.

Ubiquitous influence of wildfire emissions and secondary organic aerosol on summertime atmospheric aerosol in the forested Great Lakes region

“…The average ozone concentration was 17 ± 6 ppb ( Fig. 1), similar to previous measurements at UMBS during background air mass influence (Cooper et al, 2001). Despite the lack of direct wildfire influence (Fig.…”

“…1). The average ozone concentration was elevated at an average of 41 ± 12 ppb similar to previous measurements by Cooper et al (2001) at UMBS when under the direct influence of urban pollution (Fig. 1).…”

“…S1 and S2 in the Supplement), representative of periods observed during previous UMBS summer studies (Cooper et al, 2001;VanReken et al, 2015). Analysis of NOAA HYSPLIT backward air mass trajectories showed four distinct air mass time periods (Fig.…”

Unraveling the complex local-scale flows influencing ozone patterns in the southern Great Lakes of North America

“…The impact of the North American Great Lakes on pollution levels has been studied since the 1960's (e.g., Mukammal, 1965;Cole, 1973, 1976;Anlauf et al, 1975;Keeler et al, 1990;Sillman et al, 1993;Dye et al, 1995;Hanna and Chang, 1995;Hastie et al, 1999;Cooper et al, 2001;Fast andHeilman, 2003, 2005). These multi-year observations combined with model output suggest that ozone is systematically higher over the lakes.…”

“…The authors postulate that the origin of these polluted air masses is emissions from source areas that are entrained over the lake by the land breeze at night. Fast and Heilman (2005) used the PE-GASUS air-quality model to evaluate ozone levels over the Great Lakes region for two summers (May-September 1999 and2001). Ozone exceedances above 60 and 80 ppbv were found to be higher on average over the southern Great Lakes than over land.…”