Laboratory studies of the chemical composition and cloud condensation nuclei (CCN) activity of secondary organic aerosol (SOA) and oxidized primary organic aerosol (OPOA)

Secondary organic aerosol (SOA) and oxidized primary organic aerosol (OPOA) were produced in laboratory experiments from the oxidation of fourteen precursors representing atmospherically relevant biogenic and anthropogenic sources. The SOA and OPOA particles were generated via controlled exposure of precursors to OH radicals and/or O<sub>3</sub> in a Potential Aerosol Mass (PAM) flow reactor over timescales equivalent to 1–20 days of atmospheric aging. Aerosol mass spectra of SOA and OPOA were measured with an Aerodyne aerosol mass spectrometer (AMS). The fraction of AMS signal at <i>m/z</i> = 43 and <i>m/z</i> = 44 (<i>f</i><sub>43</sub>, <i>f</i><sub>44</sub>), the hydrogen-to-carbon (H/C) ratio, and the oxygen-to-carbon (O/C) ratio of the SOA and OPOA were obtained, which are commonly used to characterize the level of oxidation of oxygenated organic aerosol (OOA). The results show that PAM-generated SOA and OPOA can reproduce and extend the observed <i>f</i><sub>44</sub>–<i>f</i><sub>43</sub> composition beyond that of ambient OOA as measured by an AMS. Van Krevelen diagrams showing H/C ratio as a function of O/C ratio suggest an oxidation mechanism involving formation of carboxylic acids concurrent with fragmentation of carbon-carbon bonds. Cloud condensation nuclei (CCN) activity of PAM-generated SOA and OPOA was measured as a function of OH exposure and characterized as a function of O/C ratio. CCN activity of the SOA and OPOA, which was characterized in the form of the hygroscopicity parameter κ<sub>org</sub>, ranged from 8.4×10<sup>−4</sup> to 0.28 over measured O/C ratios ranging from 0.05 to 1.42. This range of κ<sub>org</sub> and O/C ratio is significantly wider than has been previously obtained. To first order, the κ<sub>org</sub>-to-O/C relationship is well represented by a linear function of the form κ<sub>org</sub> = (0.18±0.04) ×O/C + 0.03, suggesting that a simple, semi-empirical parameterization of OOA hygroscopicity and oxidation level can be defined for use in chemistry and climate models

Characterization of aerosol photooxidation flow reactors: heterogeneous oxidation, secondary organic aerosol formation and cloud condensation nuclei activity measurements

Motivated by the need to develop instrumental techniques for characterizing organic aerosol aging, we report on the performance of the Toronto Photo-Oxidation Tube (TPOT) and Potential Aerosol Mass (PAM) flow tube reactors under a variety of experimental conditions. The PAM system was designed with lower surface-area-to-volume (SA/V) ratio to minimize wall effects; the TPOT reactor was designed to study heterogeneous aerosol chemistry where wall loss can be independently measured. The following studies were performed: (1) transmission efficiency measurements for CO<sub>2</sub>, SO<sub>2</sub>, and bis(2-ethylhexyl) sebacate (BES) particles, (2) H<sub>2</sub>SO<sub>4</sub> yield measurements from the oxidation of SO<sub>2</sub>, (3) residence time distribution (RTD) measurements for CO<sub>2</sub>, SO<sub>2</sub>, and BES particles, (4) aerosol mass spectra, O/C and H/C ratios, and cloud condensation nuclei (CCN) activity measurements of BES particles exposed to OH radicals, and (5) aerosol mass spectra, O/C and H/C ratios, CCN activity, and yield measurements of secondary organic aerosol (SOA) generated from gas-phase OH oxidation of <i>m</i>-xylene and α-pinene. OH exposures ranged from (2.0 ± 1.0) × 10<sup>10</sup> to (1.8 ± 0.3) × 10<sup>12</sup> molec cm<sup>−3</sup> s. Where applicable, data from the flow tube reactors are compared with published results from the Caltech smog chamber. The TPOT yielded narrower RTDs. However, its transmission efficiency for SO<sub>2</sub> was lower than that for the PAM. Transmission efficiency for BES and H<sub>2</sub>SO<sub>4</sub> particles was size-dependent and was similar for the two flow tube designs. Oxidized BES particles had similar O/C and H/C ratios and CCN activity at OH exposures greater than 10<sup>11</sup> molec cm<sup>−3</sup> s, but different CCN activity at lower OH exposures. The O/C ratio, H/C ratio, and yield of <i>m</i>-xylene and α-pinene SOA was strongly affected by reactor design and operating conditions, with wall interactions seemingly having the strongest influence on SOA yield. At comparable OH exposures, flow tube SOA was more oxidized than smog chamber SOA, possibly because of faster gas-phase oxidation relative to particle nucleation. SOA yields were lower in the TPOT than in the PAM, but CCN activity of flow-tube-generated SOA particles was similar. For comparable OH exposures, α-pinene SOA yields were similar in the PAM and Caltech chambers, but <i>m</i>-xylene SOA yields were much lower in the PAM compared to the Caltech chamber

Relationship between Oxidation Level and Optical Properties of Secondary Organic Aerosol

Brown carbon (BrC), which may include secondary organic aerosol (SOA), can be a significant climate-forcing agent via its optical absorption properties. However, the overall contribution of SOA to BrC remains poorly understood. Here, correlations between oxidation level and optical properties of SOA are examined. SOA was generated in a flow reactor in the absence of NO_<i>x</i> by OH oxidation of gas-phase precursors used as surrogates for anthropogenic (naphthalene, tricyclo­[5.2.1.0^2,6]­decane), biomass burning (guaiacol), and biogenic (α-pinene) emissions. SOA chemical composition was characterized with a time-of-flight aerosol mass spectrometer. SOA mass-specific absorption cross sections (MAC) and refractive indices were calculated from real-time cavity ring-down photoacoustic spectrometry measurements at 405 and 532 nm and from UV–vis spectrometry measurements of methanol extracts of filter-collected particles (300 to 600 nm). At 405 nm, SOA MAC values and imaginary refractive indices increased with increasing oxidation level and decreased with increasing wavelength, leading to negligible absorption at 532 nm. Real refractive indices of SOA decreased with increasing oxidation level. Comparison with literature studies suggests that under typical polluted conditions the effect of NO_<i>x</i> on SOA absorption is small. SOA may contribute significantly to atmospheric BrC, with the magnitude dependent on both precursor type and oxidation level

Immunoglobulin domain crossover as a generic approach for the production of bispecific IgG antibodies

We describe a generic approach to assemble correctly two heavy and two light chains, derived from two existing antibodies, to form human bivalent bispecific IgG antibodies without use of artificial linkers. Based on the knobs-into-holes technology that enables heterodimerization of the heavy chains, correct association of the light chains and their cognate heavy chains is achieved by exchange of heavy-chain and light-chain domains within the antigen binding fragment (Fab) of one half of the bispecific antibody. This “crossover” retains the antigen-binding affinity but makes the two arms so different that light-chain mispairing can no longer occur. Applying the three possible “CrossMab” formats, we generated bispecific antibodies against angiopoietin-2 (Ang-2) and vascular endothelial growth factor A (VEGF-A) and show that they can be produced by standard techniques, exhibit stabilities comparable to natural antibodies, and bind both targets simultaneously with unaltered affinity. Because of its superior side-product profile, the CrossMabCH1-CL was selected for in vivo profiling and showed potent antiangiogenic and antitumoral activity