Tall Tower Vertical Profiles and Diurnal Trends of Ammonia in the Colorado Front Range
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Tall Tower Vertical Profiles and Diurnal Trends of Ammonia in the Colorado Front Range
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    Journal of Geophysical Research-Atmospheres, 122(22), 12468-12487.
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  • Description:
    Ammonia (NH3) mixing ratios were measured between the surface and 280m aboveground level from a moveable carriage at the Boulder Atmospheric Observatory tower in summer 2014 as part of the Front Range Air Pollution and Photochemistry Experiment. The campaign median mixing ratio was 3.3ppb, ranging from below detection limits to 192ppb. Median vertical profiles show an overall increase in NH3 mixing ratios toward the surface of 6.7ppb (89%) during the day and 3.9ppb (141%) at night. In contrast to the overall increasing trend, some individual profiles show decreasing NH3 in the lowest 10m. This suggests that the local surface is capable of acting as either a source or a sink, depending on the relative amounts of NH3 at the surface, and in advected air parcels. We further use this data set to investigate the variation in diurnal patterns of NH3 as a function of height above the surface. At higher altitudes (1005 and 2805m), NH3 mixing ratios reach a gradual maximum during the day between 9:00 and 16:00 local time, likely driven by changes in source region. At lower altitudes (105m), the daytime maximum begins earlier at about 7:00 local time, followed by a sharper increase at 9:00 local time. At this height we also observe a peak in NH3 mixing ratios during the night, likely driven by the trapping of emitted NH3 within the shallower nocturnal boundary layer. Plain Language Summary Atmospheric ammonia has wide ranging impacts on environmental and human health. Although it has strong sources and sinks at the earth's surface, not many studies have investigated the way that its concentration changes with altitude in the first few hundred meters above the ground. Here we present ammonia measurements made from a tall tower showing changes in ammonia concentration with height and the way that these changes can differ throughout the hours of the day. This information can be important to better understand the processes that impact ammonia concentrations and to improve our ability to represent these processes in models.
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