[1] The formation of secondary organic aerosol (SOA) in an anthropogenic-influenced region in the southeastern United States is investigated by a comparison with urban plumes in the northeast. The analysis is based on measurements of fine-particle organic compounds soluble in water (WSOC) as a measure of secondary organic aerosol. Aircraft measurements over a large area of northern Georgia, including the Atlanta metropolitan region, and in plumes from New York City and surrounding urban regions in the northeast show that fine-particle WSOC are spatially correlated with vehicle emission tracers (e.g., CO), yet the measurements indicate that vehicles do not directly emit significant particulate WSOC. In addition to being correlated, WSOC concentrations were in similar proportions to anthropogenic tracers in both regions, despite biogenic volatile organic compounds (VOCs) that were on average 10-100 times higher over northern Georgia. In contrast, radiocarbon analysis on WSOC extracted from integrated filters deployed in Atlanta suggests that roughly 70-80% of the carbon in summertime WSOC is modern. If both findings are valid, the combined results indicate that in northern Georgia, fine-particle WSOC was secondary and formed through a process that involves mainly modern biogenic VOCs but which is strongly linked to an anthropogenic component that may largely control the mass of SOA formed. Independent of the radiocarbon results, a strong association between SOA and anthropogenic sources has implications for control strategies in urban regions with large biogenic VOC emissions.Citation: Weber, R. J., et al. (2007), A study of secondary organic aerosol formation in the anthropogenic-influenced southeastern United States,

Hydroxyapatites (HAP m -T) of varying molar Ca/P ratios m (1.58−1.69) and calcination temperatures T (360−700 °C) were prepared and comprehensively characterized by nitrogen adsorption, TG, XPS, XRD, CO 2 -TPD, and NH 3 -TPD and were employed to catalyze the gas-phase dehydration of lactic acid (LA) to produce acrylic acid (AA). While the texture and crystallinity of the HAP m -T sample were affected little by variation of m, its surface acidity decreased but basicity increased with the increase in m. The HAP m -T sample with a higher T showed a higher crystallinity but lower surface area, acidity, and basicity. The conversion of LA decreased with increasing either m or T of the HAP m -T catalyst; the selectivity for AA maximized at m = 1.62 but decreased steadily with the T increase. The HAP 1.62 -360 sample (m = 1.62, T = 360 °C) was identified as the most efficient catalyst, offering an AA yield as high as 50−62% for longer than 8 h (AA selectivity: 71− 74 mol %) under optimized reaction conditions (360 °C, WHSV LA = 1.4−2.1 h −1 ). Correlating the catalyst performance with its surface acidity and basicity disclosed that the LA consumption rate increased linearly with the acidity/basicity ratio, but volcanotype dependence appeared between the AA production rate and the acidity/basicity ratio, which reveals a kind of cooperative acid−base catalysis for selective AA production. The HAP m -T catalysts became more or less deactivated after reaction, but the reacted ones could be fully regenerated by in situ treatment with flowing air.

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Gas-phase dehydration of lactic acid (LA) to acrylic acid (AA) was investigated over alkali-exchanged β zeolite (M(x)Na(1-x)β, M=Li(+), K(+), Rb(+), or Cs(+)) of different exchange degrees (x). The reaction was conducted under varying conditions to understand the catalyst selectivity for AA production and trends of byproduct formation. The nature and exchange degree of M(+) were found to be critical for the acid-base properties and catalytic performance of the exchanged zeolite. K(x)Na(1-x)β of x=0.94 appeared to be the best performing catalyst whereas Li(x)Na(1-x)β and Naβ were the poorest in terms of AA selectivity and yield. The AA yield as high as 61 mol % (selectivity: 64 mol %) could be obtained under optimized reaction conditions for up to 8 h over the best performing K0.94Na0.06β. The acid and base properties of the catalysts were probed, respectively by temperature-programmed desorption (TPD) of adsorbed NH3 and CO2, and were related to the electrostatic potentials of the alkali ions in the zeolite, which provided a basis for the discussion of the acid-base catalysis for sustainable AA formation from LA.

Twenty-four hour integrated filter samples of fine particulate matter (PM2.5) were collected from May 2004 to April 2005 at one rural site and three urban sites located in the southeastern United States. Filters were extracted and analyzed for both biogenic secondary organic aerosol (SOA) tracers via gas chromatography-mass spectrometry (GC-MS), and water-soluble organic carbon (WSOC) concentrations. The tracers reported in this study include isoprene-derived 2-methylthreitol and 2-methylerythritol, as well as pinene-derived cis-pinonic acid. The mean ambient concentrations ranged from 21.7 to 94.3 ng/m3, 5.31 to 17.9 ng/m3, and 1.87 to 3.18 microgC/m3 for 2-methyltetrols (sum of 2-methylerythritol and 2-methylthreitol), cispinonic acid and WSOC, respectively. Distinct spatial distributions were observed for all tracers with the highest concentration at the rural site and the lowest level at a coastal site. Although 2-methyltetrols were small fractions of WSOC, varying from 0.35% at an urban site to highest fractions of 1.09% at the rural site, WSOC exhibited significant correlation with 2-methyltetrols during summer, suggesting isoprene SOA makes an important contribution to WSOC. 2-Methyltetrols had the highest concentrations during the summer,when high temperature, intense solar radiation, and high ozone level occurred. However, no obvious seasonal variation was found for cispinonic acid. Between inland sites WSOC was more spatially homogeneous than the 2-methyltetrols, suggesting that WSOC was produced from a variety of mechanisms.

Development of high-performance solid acid catalysts for chemicals and materials production from bioresourced feedstock has become an important research topic in heterogeneous catalysis for renewable energy and green chemistry. We provide herein a comprehensive study on the catalytic performance of various K +exchanged zeolites (K x Na 1-x Z_y, x = 0.90−0.98) with similar molar K/Al ratios for acrylic acid (AA) production by gas-phase dehydration of lactic acid (LA) and discuss the effects of zeolite type (Z = ZSM-22, ZSM-35, MCM-22, ZSM-11, ZSM-5, ZSM-5/ ZSM-11, and β) and SiO 2 /Al 2 O 3 ratio (y). ZSM-5 and β are found more efficient than the other zeolites for this LA-to-AA reaction. Variation of y in the zeolite (β and ZSM-5) is shown to significantly affect the catalytic performance: not only higher AA selectivity and yield but also better catalytic stability is achieved by lowering y. A K 0.97 Na 0.03 ZSM-5_27 is then identified as the best-performing catalyst, offering very high AA selectivity (80−81 mol%) and yield (74−78 mol%) at 360 °C under high LA space velocity (WHSV LA = 2.1 h −1 ). This catalyst also shows a remarkable long-term stability, being capable to maintain a high AA selectivity (>70 mol%) and yield (>55 mol%) for longer than 80 h. Furthermore, an in situ calcination of the used catalyst with flowing air at 450 °C is shown to be efficient for complete catalyst regeneration. Correlating the catalyst performance with its surface acid− base property measured by NH 3 -and CO 2 -TPD clearly uncovers that balance between the surface acidity and basicity would be a key, besides Z and y of the zeolite, to the catalyst performance.

An unanticipated wind shift led to the advection of plumes from two prescribed burning sites that impacted Atlanta, GA, producing a heavy smoke event late in the afternoon on February 28, 2007. Observed PM2.5 concentrations increased to over 140 microg/m3 and O3 concentrations up to 30 ppb in a couple of hours, despite the late hour in February when photochemistry is less vigorous. A detailed investigation of PM2.5 chemical composition and source apportionment analysis showed that the increase in PM2.5 mass was driven mainly by organic carbon (OC). However, both results from source apportionment and an observed nonlinear relationship between OC and PM2.5 potassium (K) indicate that the increased OC was not due solely to primary emissions. Most of the OC was water-soluble organic carbon (WSOC) and was dominated by hydrophobic compounds. The data are consistent with large enhancements in isoprenoid (isoprene and monoterpenes) and other volatile organic compounds emitted from prescribed burning that led to both significant O3 and secondary organic aerosol (SOA) production. Formation of oligomers from oxidation products of isoprenoid compounds or condensation of volatile organic compounds (VOCs) with multiple functional groups emitted during prescribed burning appears to be a major component of the secondary organic contributor of the SOA. The results from this study imply that enhanced emissions due to the fire itself and elevated temperature in the burning region should be considered in air quality models (e.g., receptor and emission-based models) to assess impacts of prescribed burning emissions on ambient air quality.

Rb + -and Cs + -exchanged Beta zeolites (Rb x Na 1-x β and Cs x Na 1-x β) of varying exchange degrees (x = 0~1.00) were employed to catalyze the gas-phase dehydration of lactic acid (LA) for sustainable production of acrylic acid (AA) in a flow fixed-bed reactor at 360 o C, using an aqueous solution of LA (10 mol% or 35.7%) as the reaction feed at a weight hourly space velocity by LA of 2.1 h -1 . An appropriate window of the ion exchange degrees for highly selective AA production (≥ 60 mol%) was determined for either series of the samples, i.e., x = 0.85~0.98 for the Rb x Na 1-x β and x = 0.71~0.90 for the Cs x Na 1-x β samples. The best performing catalysts Rb 0.95 Na 0.05 β, and Cs 0.81-0.90 Na 0.19-0.10 β offered the highest AA selectivity (ca. 70 mol%) and yield (ca. 60~65 mol%) for reaction periods of longer than 10 h. Measurements of the surface acidity and basicity of the catalyst samples bytemperature-programmed desorption of NH 3 and CO 2 showed that the highly selective catalysts in such widows should have both weakly acidic and weakly basic surface sites with suitably balanced acidity and basicity. The acid-catalyzed decarbonylation/decarboxylation and base-catalyzed condensation of LA, which lead respectively to formation of acetaldehyde and 2,3-pentanedione, always occurred as the competing reactions over the investigated catalysts. Observations on the catalyst selectivity changes for these competing reactions clearly demonstrate that the suitably balanced acidity and basicity at the catalyst surface is the key to the high selectivity for the desired dehydration reaction.