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We present a holistic examination of tropospheric OH reactivity (OHR) in South Korea using comprehensive NASA DC-8 airborne measurements collected during the Korea–United States Air Quality field study and chemical transport models. The observed total OHR (tOHR) averaged in the planetary boundary layer (PBL

International audience; Reactive chlorine and bromine species emitted from snow and aerosols can significantly alter the oxidative capacity of the polar boundary layer. However, halogen production mechanisms from snow remain highly uncertain, making it difficult for most models to include descriptions of halogen snow emissions and to understand the impact on atmospheric chemistry. We investigate the influence of Arctic halogen emissions from snow on boundary layer oxidation processes using a one-dimensional atmospheric chemistry and transport model (PACT-1D). To understand the combined impact of snow emissions and boundary layer dynamics on atmospheric chemistry, we model Cl2 and Br2 primary emissions from snow and include heterogeneous recycling of halogens on both snow and aerosols. We focus on a 2-day case study from the 2009 Ocean-Atmosphere-Sea Ice-Snowpack campaign at Utqiaġvik, Alaska. The model reproduces both the diurnal cycle and high quantity of Cl2 observed, along with the measured concentrations of Br2, BrO, and HOBr. Due to the combined effects of emissions, recycling, vertical mixing, and atmospheric chemistry, reactive chlorine is typically confined to the lowest 15 m of the atmosphere, while bromine can impact chemistry up to and above the surface inversion height. Upon including halogen emissions and recycling, the concentration of HOx (HOx = OH + HO2) at the surface increases by as much as a factor of 30 at mid-day. The change in HOx due to halogen chemistry, as well as chlorine atoms derived from snow emissions, significantly reduce volatile organic compound lifetimes within a shallow layer near the surface.

Modeled source attribution information from the Community Multiscale Air Quality model was coupled with ambient data from the 2011 Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality Baltimore field study. We assess source contributions and evaluate the utility of using aircraft measured CO and NO y relationships to constrain emission inventories. We derive ambient and modeled ΔCO:ΔNO y ratios that have previously been interpreted to represent CO:NO y ratios in emissions from local sources. Modeled and measured ΔCO:ΔNO y are similar; however, measured ΔCO:ΔNO y has much more daily variability than modeled values. Sector-based tagging shows that regional transport, on-road gasoline vehicles, and nonroad equipment are the major contributors to modeled CO mixing ratios in the Baltimore area. In addition to those sources, on-road diesel vehicles, soil emissions, and power plants also contribute substantially to modeled NO y in the area. The sector mix is important because emitted CO:NO x ratios vary by several orders of magnitude among the emission sources. The model-predicted gasoline/diesel split remains constant across all measurement locations in this study. Comparison of ΔCO:ΔNO y to emitted CO:NO y is challenged by ambient and modeled evidence that free tropospheric entrainment, and atmospheric processing elevates ambient ΔCO:ΔNO y above emitted ratios. Specifically, modeled ΔCO:ΔNO y from tagged mobile source emissions is enhanced 5-50% above the emitted ratios at times and locations of aircraft measurements. We also find a correlation between ambient formaldehyde concentrations and measured ΔCO:ΔNO y suggesting that secondary CO formation plays a role in these elevated ratios. This analysis suggests that ambient urban daytime ΔCO:ΔNO y values are not reflective of emitted ratios from individual sources.

During the TRAnsport and Chemical Evolution over the Pacific-2001 (TRACE-P-2001) aircraft mission, formaldehyde (CH₂O) and acetaldehyde (CH₃CHO) were measured along with an extensive suite of other atmospheric parameters. CH₃CHO was measured with two different instruments, one developed by NCAR and another developed by NASA. There were disagreements, at times, between the CH₃CHO measurements. There was also disagreement between the CH₃CHO datasets and a simple photochemical box model, although CH₂O measurements agreed with the model. It is important to model and measure both gases correctly because they are intermediate oxidation products of volatile organic compounds (VOCs), and they decompose into hydroperoxyl radicals (HO₂) and carbon monoxide (CO). The objective of this study was to explore the relationship between CH₂O and CH₃CHO in the troposphere. The relationship of CH₂O vs. CH₃CHO was examined for five different altitude ranges up to 12 km. Each altitude range was parsed into clean and polluted air masses; “polluted” was defined as nitric oxide (NO) greater than 50 parts per trillion by volume or CO greater than 169 parts per billion by volume. Slope and linear regression correlation coefficients were compared. The following patterns were observed for the individual CH₃CHO datasets in relation to CH2O. CH₃CHO decreased with altitude, but more slowly than CH₂O. Correlation between CH₃CHO and CH₂O was driven by polluted air, although this correlation decreased with altitude.