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Abstract Ground level 24 h average observations of 7Be activity, combined with continuous ozone (O 3), carbon monoxide (CO) and minimum relative humidity (minRH) measurements, were conducted at two non-urban sites in the Deep South of the United States. One site is inland at Yorkville, Georgia, YRK (33°55′27″N; 84°59′44″W); the other is near the coast of the Gulf of Mexico outside Pensacola, Florida, OLF (30°25′N:87°13′W). The objective of the measurements was to explore the potential for estimating a contribution to surface O 3 from stratospheric and upper tropospheric air for during the springtime months from April 2 to June 13, 2015 using 7Be as a tracer. The observed 24 h average 7Be activities were 1.88 ± 0.66 mBq/m3 at YRK and 1.99 ± 0.68 mBq/m3 at OLF. Corresponding means of 24 h average O 3 mixing ratios were 38.3 ± 10.1 ppbv for YRK and 28.7 ± 8.9 ppbv at OLF. A weak statistically significant O 3 7Be regression based estimate of O 3 from the stratosphere and upper troposphere was constrained to a conservative upper bound of 14 ± 4 (1σ) ppbv. From daily inspection of meteorological features, a lower bound of 3–7 ppbv was estimated. A multiple regression of O 3 versus 7Be and daily minimum relative humidity (minRH) improved the statistical fit and indicated stratosphere-upper troposphere contributions of 8.6 ± 4.0 ppbv for YRK and 6.6 ± 3.3 ppbv for OLF. Daily variability of 7Be and O 3 was explored with respect to meteorological variability. 7Be O 3 relationships in this experiment were examined using (a) ozonesonde and vertical dew point temperature profiles, inferring very dry air as an upper atmosphere tracer descending into the boundary layer, (b) backward air trajectories, identifying 7Be spatial and temporal variation, and (c) precipitation, indicating 7Be scavenging and lowered O 3 with suppression of photochemistry. The average 7Be measurements at the ground during the study are useful for helping estimate the long-term O 3 contributions from the upper atmosphere. However, the day-to-day 7Be observations had limited value for determining the contributions of upper air O 3 to daily O 3 mixing ratios. Conventional surface and upper-air meteorological data could be used effectively as an alternative. Highlights • Springtime southeastern ozone from the upper atmosphere is a minor part of total surface ozone from Beryllium-7 activity.. • Beryllium-7 activity correlated with ozone, reactive nitrogen, minimum daily relative humidity and aerosol particles. • Calculations for ozone and Beryllium-7, reactive nitrogen or relative humidity yielded regression relations for sites. • Vertical profiles of ozone mixing ratio, temperature, relative humidity or dew point indicated surface air from aloft. • Air trajectories and weather suggest that synoptic flow, and widespread rainfall are important for Beryllium-7 variability. [ABSTRACT FROM AUTHOR]

This study describes and analyzes measurements of 119 non-polar organic compounds in PM2.5 samples from three urban sites in the Southeastern Aerosol Research and Characterization (SEARCH) network: Jefferson Street in Atlanta, Georgia (JST), Birmingham, Alabama (BHM), and Hinton, Texas (HIN). Daily 24-h PM2.5 samples were collected on quartz-fiber filters from January 2006 through 2007 at HIN and from March 2006 through 2010 at JST and BHM. PM2.5 sampling at BHM and JST is ongoing. The measured species are associated with directly emitted particles and potentially serve as tracers of specific types of emissions. PM2.5 organic measurements include 28 n-alkanes (C15-C42), 18 iso-/anteiso-alkanes (C29-C37), 2 methyl alkanes, 3 branched alkanes, 5 cycloalkanes, 32 PAH compounds, 18 hopanes, 12 steranes, and 1 alkene, many of which are constituents of motor-vehicle exhaust and other anthropogenic PM2.5 emissions. Predominantly anthropogenic origins of the measured compounds are indicated by weekly and seasonal cycles that are identified with known emission patterns, especially for motor vehicle usage. Annual mean concentrations of each class of compounds declined by 60-90% from 2006 through 2009, then increased in 2010 to concentrations comparable to 2008. These changes are similar to 40% reductions of on-road and non-road motor-vehicle exhaust PM2.5 emissions between 2006 and 2010. Year-to-year variations in OC correlated with year-to-year variations in measured non-polar compound concentrations. Regression of OC against the sums of measured n-alkanes, iso-/anteiso-alkanes, PAHs, hopanes, and steranes indicates that 32 ± 7% of OC at BHM and 35 ± 4% of OC at JST derived from sources emitting the measured non-polar compounds. The reductions in measured concentrations of EC, OC, and non-polar OC species represent an important improvement in air quality in the southeastern U.S. that can be attributed by the long-term measurement program to PM2.5 emission reductions. [ABSTRACT FROM AUTHOR]

Abstract: Volatile organic compounds (VOCs) are emitted from anthropogenic and natural (biogenic) sources into the atmosphere. Characterizing their ambient mixing ratios or concentrations is a challenge because VOCs comprise hundreds of species, and accurate measurements are difficult. Long-term hourly and daily-resolution data have been collected in the metropolitan area of Atlanta, Georgia, a major city dominated by motor vehicle emissions. A series of observations of daily, speciated C2–C10 non-methane organic compounds (NMOC) and oxygenated hydrocarbons (OVOC) in mid-town Atlanta (Jefferson Street, JST) are compared with data from three urban-suburban sites and a nearby non-urban site. Annual-average mixing ratios of NMOC and OVOC at JST declined from 1999 through 2007. Downward trends in NMOC, CO, and NOy corroborate expected emission changes as reflected in emission inventories for Atlanta’s Fulton County. Comparison of the JST NMOC composition with data from roadside and tunnel sampling reveals similarities to motor vehicle dominated samples. The JST annual average VOC-OH reactivities from 1999 to 2007 were relatively constant compared with the decline in annual-average NMOC mixing ratios. Mean reactivity at JST, in terms of concentration*kOH, was approximately 40% alkenes, 22% aromatics, 16% isoprene and 6% other biogenics, 13% C7–C10 alkanes and 3% C2-C6 alkanes, indicating that biogenic NMOCs are important but not dominant contributors to the urban reactive NMOC mix. In contrast, isoprene constituted ∼50% of the VOC-OH reactivities at two non-urban sites. Ratios of 24-hour average CO/benzene, CO/isopentane, and CO/acetylene concentrations indicate that such species are relatively conserved, consistent with their low reactivity. Ratios of more-reactive to less-reactive species show diurnal variability largely consistent with expected emission patterns, transport and mixing of air, and chemical processing. [Copyright &y& Elsevier]