Deliquescence Relative Humidities of Organic and Inorganic Salts Important in the Atmosphere.

The deliquescence relative humidities (DRH) as a function of temperature have been determined for several salts of atmospheric importance using humidity controlled thermogravimetric analysis (HTGA): sodium hydrogen oxalate monohydrate (NaHC2O4·H2O), sodium oxalate (Na2C2O4), sodium ammonium sulfate dihydrate (NaNH4SO4·2H2O, lecontite), sodium hydrogen malonate monohydrate (NaHC3H2O4·H2O), sodium malonate monohydrate (Na2C3H2O4·H2O), and ammonium hydrogen malonate (NH4HC3H2O4). The temperature-dependent onset DRH values (where a dry mixture begins to take up water) were also determined for mixtures of ammonium sulfate with malonic acid, and ammonium sulfate with sodium oxalates and sodium malonates, respectively. We demonstrate that the onset DRH is independent of the ratio of solids in the mixture. In general, onset DRH values were always lower than the pure component DRH values.

Temperature-dependent deliquescence relative humidities and water activities using humidity controlled thermogravimetric analysis with application to malonic acid.

We utilize a new experimental technique, humidity-controlled thermogravimetric analysis (HTGA), to determine temperature-dependent deliquescence relative humidities (DRH) and to determine the equilibrium concentration of a solution at a given temperature and relative humidity. To that end, we have investigated the malonic acid/water system determining the DRH and concentration/RH relationship in the temperature range 303-278 K. Excellent agreement is found with literature values for the DRH of malonic acid as a function of temperature and for the concentration/RH relationship at several temperatures. Thus, we extend the DRH and concentration/RH relationship to a broader temperature range and are using the HTGA experiments to investigate other organic acids.

Solid/liquid phase diagram of the ammonium sulfate/malic acid/water system.

We have studied the low temperature phase diagram and water activities of the ammonium sulfate/malic acid/water system using differential scanning calorimetry (DSC) and infrared spectroscopy (IR) of thin films. Using the results from our experiments we have mapped the ice primary phase region of the solid/liquid ternary phase diagram. In our DSC and IR experiments we observe ice nucleation in all samples and ammonium sulfate in some samples, which were cooled to 183 K. However, we only observed malic acid nucleation in IR experiments, where the sample was in contact with ZnSe windows. We also compare our results to the predictions of the Extended AIM Aerosol Thermodynamics Model (E-AIM) and find good agreement for the ice melting points in the ice primary phase field of this system; however, the E-AIM has difficulty predicting malic acid crystallization.

Solid/Liquid phase diagram of the ammonium sulfate/maleic acid/water system.

We have studied the low temperature phase diagram and water activities of the ammonium sulfate/maleic acid/water system using differential scanning calorimetry and infrared spectroscopy of thin films. Using the results from our experiments, we have mapped the solid/liquid ternary phase diagram, determined the water activities based on the freezing point depression, and determined the ice/maleic acid phase boundary as well as the ternary eutectic composition and temperature. We also compare our results to the predictions of the extended AIM aerosol thermodynamics model and find good agreement for the ice melting points in the ice primary phase field of this system; however significant differences were found with respect to phase boundaries, maleic acid dissolution, and ammonium sulfate dissolution.

Taehwa Research Forest: A receptor site for severe domestic pollution events in Korea during 2016.

During the May-June 2016 International Cooperative Air Quality Field Study in Korea (KORUS-AQ), light synoptic meteorological forcing facilitated Seoul metropolitan pollution outflow to reach the remote Taehwa Research Forest (TRF) site and cause regulatory exceedances of ozone on 24 days. Two of these severe pollution events are thoroughly examined. The first, occurring on 17 May 2016, tracks transboundary pollution transport exiting eastern China and the Yellow Sea, traversing the Seoul Metropolitan Area (SMA), and then reaching TRF in the afternoon hours with severely polluted conditions. This case study indicates that although outflow from China and the Yellow Sea were elevated with respect to chemically unperturbed conditions, the regulatory exceedance at TRF was directly linked in time, space, and altitude to urban Seoul emissions. The second case studied, occurring on 09 June 2016, reveals that increased levels of biogenic emissions, in combination with amplified urban emissions, were associated with severe levels of pollutions and a regulatory exceedance at TRF. In summary, domestic emissions may be causing more pollution than by trans-boundary pathways, which have been historically believed to be the major source of air pollution in South Korea. The case studies are assessed with multiple aircraft, model (photochemical and meteorological) simulations, in-situ chemical sampling, and extensive ground-based profiling at TRF. These observations clearly identify TRF and the surrounding rural communities as receptor sites for severe pollution events associated with Seoul outflow, which will result in long-term negative effects to both human health and agriculture in the affected areas.

Formaldehyde column density measurements as a suitable pathway to estimate near-surface ozone tendencies from space.

In support of future satellite missions that aim to address the current shortcomings in measuring air quality from space, NASA's Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) field campaign was designed to enable exploration of relationships between column measurements of trace species relevant to air quality at high spatial and temporal resolution. In the DISCOVER-AQ data set, a modest correlation (r 2 = 0.45) between ozone (O3) and formaldehyde (CH2O) column densities was observed. Further analysis revealed regional variability in the O3-CH2O relationship, with Maryland having a strong relationship when data were viewed temporally and Houston having a strong relationship when data were viewed spatially. These differences in regional behavior are attributed to differences in volatile organic compound (VOC) emissions. In Maryland, biogenic VOCs were responsible for ~28% of CH2O formation within the boundary layer column, causing CH2O to, in general, increase monotonically throughout the day. In Houston, persistent anthropogenic emissions dominated the local hydrocarbon environment, and no discernable diurnal trend in CH2O was observed. Box model simulations suggested that ambient CH2O mixing ratios have a weak diurnal trend (±20% throughout the day) due to photochemical effects, and that larger diurnal trends are associated with changes in hydrocarbon precursors. Finally, mathematical relationships were developed from first principles and were able to replicate the different behaviors seen in Maryland and Houston. While studies would be necessary to validate these results and determine the regional applicability of the O3-CH2O relationship, the results presented here provide compelling insight into the ability of future satellite missions to aid in monitoring near-surface air quality.

Haptotropic rearrangement in tricarbonylchromium complexes of 2-aminobiphenyl and 4-aminobiphenyl.

The para-aminobiphenyl compound [(η(6)-C(6)H(5))(C(6)H(4)-4-NH(2))]Cr(CO)(3) (1) has an arene-phenyl dihedral angle of 38.01(6)°, as determined by single-crystal X-ray crystallography, and 34.7(11)°, as determined by DFT calculations. It undergoes haptotropic rearrangement at 140 °C in solution to form [(η(6)-C(6)H(4)-4-NH(2))(C(6)H(5))]Cr(CO)(3) (2), even though previous reports have suggested that such rearrangements should not be observed in compounds with arene-phenyl dihedral angles greater than 22°. NMR analysis gave a rate constant of k = 5.0 × 10(-5) s(-1) for the rearrangement of 1 to 2. The ortho-substituted analog [(η(6)-C(6)H(5))(C(6)H(4)-2-NH(2))]Cr(CO)(3) (3) has an arene-phenyl dihedral angle of 67.70(7)°, as determined by single-crystal X-ray crystallography, and 51.9(10)°, as determined by DFT calculations. Surprisingly, even though it displays a more extreme canting of arene rings, 3 rearranges to [(η(6)-C(6)H(4)-2-NH(2))(C(6)H(5))]Cr(CO)(3) (4) at 140 °C in solution with a rate constant of k = 2.6 × 10(-4) s(-1). This approximately five-fold rate enhancement likely results from the ortho-amino group providing intramolecular stabilization for intermediates formed during the rearrangement.