Ground‐based High Spectral Resolution Lidar observation of aerosol vertical distribution in the summertime Southeast United States

Abstract

As part of the Southeast United States‐based Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS), and collinear with part of the Southeast Atmosphere Study, the University of Wisconsin High Spectral Resolution Lidar system was deployed to the University of Alabama from 19 June to 4 November 2013. With a collocated Aerosol Robotic Network (AERONET) sun photometer, a nearby Chemical Speciation Network (PM2.5) measurement station, and near daily ozonesonde releases for the August–September SEAC4RS campaign, the site allowed the region's first comprehensive diurnal monitoring of aerosol particle vertical structure. A 532 nm lidar ratio of 55 sr provided good closure between aerosol backscatter and AERONET (aerosol optical thickness, AOT). A principle component analysis was performed to identify key modes of variability in aerosol backscatter. “Fair weather” days exhibited classic planetary boundary layer structure of a mixed layer accounting for ~50% of AOT and an entrainment zone providing another 25%. An additional 5–15% of variance is gained from the lower free troposphere from either convective detrainment or frequent intrusions of western United States biomass burning smoke. Generally, aerosol particles were contained below the 0°C level, a common level of stability in convective regimes. However, occasional strong injections of smoke to the upper troposphere were also observed, accounting for the remaining 10–15% variability in AOT. Examples of these common modes of variability in frontal and convective regimes are presented, demonstrating why AOT often has only a weak relationship to surface PM2.5 concentration.

Assessing the Challenges of Surface‐Level Aerosol Mass Estimates From Remote Sensing During the SEAC4RS and SEARCH Campaigns: Baseline Surface Observations and Remote Sensing in the Southeastern United States

“…The summer and fall periods are delineated by 20 September 2012. Extinction is here calculated assuming a uniform lidar ratio of 55 str as used by Reid et al (). As expected, extinction is higher in the summer months commensurate with higher AOD.…”

“…As part of SEAC 4 RS, the University of Alabama, Huntsville (UAH), site employed a Sun photometer and measured basic meteorological parameters and was 5 km from an EPA Chemical Speciation Network (CSN) site (U.S. Environmental Protection Agency, ), which afforded hourly PM 2.5 mass, and aerosol chemistry measurements made once every six days. Also at the UAH site was the addition of a University of Wisconsin (UW) Space Sciences and Engineering Center (SSEC) 532 nm high spectral resolution lidar (HSRL) to the University of Alabama Huntsville (UAH) National Space Sciences Technology Center (NSSTC) Regional Atmospheric Profiling Center for Discovery (RAPCD) lidar facility (UW HSRL), providing near continuous profiles of aerosol backscatter (Reid et al, ). Between the SEARCH and UAH sites, we have the ability to regionally monitor AOD‐PM 2.5 relationships and intensive particle scattering and chemistry properties at daily to hourly sampling all spaced ~250 km apart in a roughly 500 × 250 km domain covering portions of the Florida panhandle, Alabama, and northwest Georgia.…”

Ozone Variability and Anomalies Observed During SENEX and SEAC4RS Campaigns in 2013

“…The air quality of Huntsville can be largely considered as slightly polluted rural, given that ozone in the planetary boundary layer (PBL) at Huntsville is higher than unpolluted, background stations (e.g., Trinidad Head, California; Boulder, Colorado; and Wallops Island, Virginia) (Newchurch et al, ; Stauffer et al, ), especially during the summer, but lower than polluted metropolitan cities (e.g., Houston) (Morris et al, ). Although industrial emissions in Huntsville are minor, this city is sometimes affected by pollution transport on various spatial scales (Kuang et al, ; Reid et al, ).…”

Status and future of numerical atmospheric aerosol prediction with a focus on data requirements

“…Only recently have products like aerosol size distribution, aerosol scattering, or absorption coefficients become available in NRT from a limited number of stations. However, the ability of a model to reproduce AOD at a station or even a region may not always be a good indicator of its performance to reproduce surface concentration or vertical aerosol distribution Reid et al, 2017), even though these model variables are clearly interconnected. Therefore, and in the absence of emissions and deposition routine observations, model evaluation should combine atmospheric-column-integrated variables with vertical profiles (extinction coefficient at a reference wavelength at 550 nm to provide information about the height and thickness of the aerosol layer), and surface measurements (such as PM 10 , PM 2.5 , and PM 1 ).…”