Chemical climatology of the southeastern United States, 1999–2013

Abstract

Abstract. A series of experiments (the Southern Oxidant and Aerosol Study-SOAS) took place in central Alabama in June–July 2013 as part of the broader Southern Atmosphere Study (SAS). These projects were aimed at studying oxidant photochemistry and formation and impacts of aerosols at a detailed process level in a location where high biogenic organic vapor emissions interact with anthropogenic emissions, and the atmospheric chemistry occurs in a subtropical climate in North America. The majority of the ground-based experiments were located at the Southeastern Aerosol Research and Characterization (SEARCH) Centreville (CTR) site near Brent, Alabama, where extensive, unique aerometric measurements of meteorology, trace gases and particles have been made from the early 1990s through 2013. The SEARCH network data permits a characterization of temporal and spatial context of the SOAS findings. The long-term measurements show that the SOAS experiments took place during the second wettest and coolest year in the 2000–2013 period, with lower than average solar radiation. The pollution levels at CTR and other SEARCH sites were the lowest since full measurements began in 1999. This dataset provides a perspective for the SOAS program in terms of long-term average chemistry (chemical climatology) and short-term comparisons of summer average spatial variability across the Southeast at high temporal (hourly) resolution. Changes in anthropogenic gas and particle emissions between 1999 and 2013, account for the decline in pollutant concentrations at the monitoring sites in the region. The long-term and short-term data provide an opportunity to contrast SOAS results with temporally and spatially variable conditions in support for the development of tests for the robustness of SOAS findings.

Recent trends in gas-phase ammonia and PM2.5 ammonium in the Southeast United States

“…As noted earlier, this trend is anticipated, as SO 2 and NO x emissions and SO 2 and NO y measured concentrations (Blanchard et al, 2013) (Blanchard et al, 2013;Hidy et al, 2014), largely due to decreasing ammonium sulfate and ammonium nitrate components ultimately caused by decreasing SO 2 and NO x emissions over the period.…”

Evaluating Summer-Time Ozone Enhancement Events in the Southeast United States

“…Precursor gases leading to O 3 formation/destruction (e.g., CO, CH 4 , VOCs, and NO x ) in the troposphere are emitted from anthropogenic sources (e.g., fossil fuel combustion, vehicle emissions), wildfires and biomass burning, and natural sources (e.g., lightning NO x , soils, and vegetation). The southeast US is a unique region which is largely impacted by all the aforementioned sources of O 3 and precursor gas emissions [11]. The numerous sources of O 3 and precursor gases and complex atmospheric chemistry controlling the air quality of the southeast US is currently of large scientific interest which has led to multiple measurement campaigns focused on aerosol and trace gas concentrations during the summer months (e.g., Southern Oxidant and Aerosol Study (SOAS), Studying the Interactions Between Natural and Anthropogenic Emissions at the Nexus of Climate Change and Air Quality (SENEX), and Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC 4 RS)).…”

Effects of temperature-dependent NO<sub><i>x</i></sub> emissions on continental ozone production

“…2 can be compared to the observed behavior during SOAS (SOAS Science Team, 2013). Measurements during SOAS have been described in detail elsewhere (e.g., Hidy et al, 2014;Romer et al, 2016;Feiner et al, 2016) and are summarized below. The primary ground site for SOAS was co-located with the CTR site of the SEARCH network (32.90289 • N, 87.24968 • W), in a clearing surrounded by a dense mixed forest (Hansen et al, 2003).…”