A lidar study of the spatial and temporal variability of aerosol pollution over New Haven, CT

Aerosol particles and clouds are key components of the climate system, but their complex interactions and net effects are currently poorly understood. Anthropogenic aerosols, including sulfate, black carbon, nitrate and dust, have been shown to have cooling effects on climate, but the magnitude of this cooling is unclear (IPCC, 2007). Determining how aerosols and clouds are distributed vertically in the atmosphere is crucial for their integration in climate models and also for understanding aerosol effects on air quality. This study evaluates spatial and temporal patterns of aerosol and cloud variability over an urban environment, New Haven, in the summer and fall of 2013. Boundary layer dynamics and aerosol optical depths (AOD) are analyzed based on vertical profiles retrieved with a ground-based lidar that emits pulses of UV light (wavelength 355nm) into the atmosphere. Aerosol optical depth statistics and patterns of aerosol accumulation will be presented. Mean daily aerosol optical depth from June-July 2013 was 0.268, with a peak daily mean of 0.495. Aerosol spatial distributions are found to depend on meteorological conditions, but three characteristic regimes were observed and will be described: one of diurnal peaks in particle loading, one of midday lifting of aerosols accumulated in the boundary layer, and one marked by the presence of lofted, nonlocal aerosols. The study identifies high-pollution events for further study based on rapid increases in AOD, such as from a mean value of 0.225 to 0.393 on consecutive days July 8-9. The origins of polluted, nonlocal air parcels, which are often lofted and distinct from an underlying boundary layer, will be discussed based on data from local weather stations. The present study characterizes the typical aerosol concentrations and distributions over New Haven in summer and fall, enhancing our understanding of urban atmospheric impacts.