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A Spatially Dense Aerosol Instrument Network in the Southern Great Plains: POPSnet-SGP

E. Asher1,2, T. Thornberry2, D. Fahey2, A.C. McComiskey3, K. Chang1,2, K.S. Carlaw4, L. Grunau5 and R. Gao2

1Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO 80309; 512-587-2684, E-mail: elizabeth.asher@noaa.gov
2NOAA Chemical Sciences Laboratory (CSL), Boulder, CO 80305
3Department of Energy's Brookhaven National Laboratory, Upton, NY 11973
4University of Leeds, Leeds, United Kingdom
5Formerly of the University of Leeds, Leeds, United Kingdom

The sparseness of aerosol microphysical measurements has limited our understanding of global aerosol emissions, transport, and radiative effects. The Portable Optical Particle Spectrometer network – Southern Great Plains (POPSnet-SGP) project deployed a spatially dense and nearly autonomous ground-based network of in situ aerosol measurements at 7 sites across a 150 km x 150 km region of relatively homogenous terrain at the Department of Energy Aerosol Radiation Measurement (ARM) Southern Great Plains (SGP) facility in Oklahoma in October, 2019. We show how the POPSnet-SGP near-surface, ambient measurements of particle number and size at multiple locations allow an assessment of the statistical representativeness of a single surface measurement under background continental conditions using data collected between October, 2019 – March, 2019.  Measurement uncertainty at individual sites, using pairs of POPS instruments at each site when possible, as well as the inherent uncertainty in aerosol sizing were considered. Overall, we observe high coherence between aerosol concentrations and aerosol size distributions at each site, however periods of significant short-term variability between individual sites and the network mean value occur, often influenced by differences in local meteorology.  In our study, representation error decreased with larger averaging periods and varied by site.  Interestingly, the measurement representation error also appeared higher for aerosol concentration with diameter > 400 nm (and to a lesser extent aerosol surface area) than for total aerosol concentration, due to differences in the observed concentrations of medium sized accumulation mode aerosols (410 - 670 nm).  Long-term monitoring of representation error at ARM-SGP and studies in other regions will be needed to confirm this finding.  We suggest that the POPSnet approach provides considerably more insight into the spatial variability in the aerosol population that can be used to constrain climate models than would be available from similar networks of PM 2.5 monitors. 

Figure 1

Figure 1. Locations and photos of POPSnet-SGP enclosures installed at the central facility (C1) and six extended facility (E/EF) sites. Sites are located in rural areas and shown in different colors, with the altitude of each listed in meters.

Figure 2

Figure 2. Labeled photo (a) and schematic (b) of a POPSnet-SGP enclosure. In the schematic, the plumbing is shown from a sideview, and electrical power connections are shown in green and data transfer is shown in blue.