Solar Absorption by Aerosol-Bound Nitrophenols Compared to Aqueous and Gaseous Nitrophenols

Nitrophenols are well-known absorbers of near-UV/blue radiation and are considered to be a component of solar-absorbing organic aerosol material commonly labeled brown carbon. Nitrophenols have been identified in a variety of phases in earth’s atmosphere, including the gaseous, aqueous, and aerosol bound, and these different environments alter their UV–vis absorption spectra, most dramatically when deprotonated forming nitrophenolates. We quantify the impact of these different absorption profiles by calculating the solar power absorbed per molecule for several nitrophenols. For instance, aqueous 2,4-dinitrophenol absorption varies dramatically over the pH range of cloud droplets with pH = 5.5 solutions absorbing three times the solar power compared to pH = 3.5 solutions. We also measured the UV–vis spectra of 2-nitrophenol adsorbed on several aerosol substrates representative of mineral dust, inorganic salts, and organic aerosol and compare these spectra to gaseous and aqueous 2-nitrophenol. 2-Nitrophenol adsorbed on mineral and chloride aerosol substrates exhibits a red-shifted absorption band (∼450–650 nm) consistent with 2-nitrophenolate and absorbs twice the solar power per molecule compared to gaseous, aqueous, and organic aerosol-bound 2-nitrophenol. We also discuss how different nitrophenol absorption profiles alter important atmospheric photolysis rate constants [e.g., <i>J</i>(NO₂) and <i>J</i>(O₃)] by attenuating solar flux

Multiphase Ozonolysis of Aqueous α‑Terpineol

Multiphase ozonolysis of aqueous organics presents a potential pathway for the formation of aqueous secondary organic aerosol (aqSOA). We investigated the multiphase ozonolysis of α-terpineol, an oxygenated derivative of limonene, and found that the reaction products and kinetics differ from the gas-phase ozonolysis of α-terpineol. One- and two-dimensional NMR spectroscopies along with GC-MS identified the aqueous ozonolysis reaction products as <i>trans</i>- and <i>cis</i>-lactols [4-(5-hydroxy-2,2-dimethyltetrahydrofuran-3-yl)­butan-2-one] and a lactone [4-hydroxy-4-methyl-3-(3-oxobutyl)-valeric acid gamma-lactone], which accounted for 46%, 27%, and 20% of the observed products, respectively. Hydrogen peroxide was also formed in 10% yield consistent with a mechanism involving decomposition of hydroxyl hydroperoxide intermediates followed by hemiacetal ring closure. Multiphase reaction kinetics at gaseous ozone concentrations of 131, 480, and 965 parts-per-billion were analyzed using a resistance model of net ozone uptake and found the second-order rate coefficient for the aqueous reaction of α-terpineol + O₃ to be 9.9(±3.3) × 10⁶ M^–1 s^–1. Multiphase ozonolysis will therefore be competitive with multiphase oxidation by hydroxyl radicals (OH) and ozonolysis of gaseous α-terpineol. We also measured product yields for the heterogeneous ozonolysis of α-terpineol adsorbed on glass, NaCl, and kaolinite, and identified the same three major products but with an increasing lactone yield of 33, 49, and 55% on these substrates, respectively

Ozone Decomposition on Kaolinite as a Function of Monoterpene Exposure and Relative Humidity

Atmospheric processing of mineral aerosol by trace gases results in the formation of surface-adsorbed products that have the capacity to alter the chemical and physical properties of these airborne particulates. To investigate one potential impact of aerosol processing by biogenic volatile organic compounds (BVOCs), we investigated the heterogeneous decomposition of ozone on pure and monoterpene-processed kaolinite. We used a laminar flow reactor to measure O₃ reactive uptake coefficients on kaolinite-coated tubes as a function of relative humidity, O₃ concentration, and pre-exposure to gaseous limonene and α-pinene. At 26% RH, kaolinite has a near equivalent of a monolayer of adsorbed water, and the ozone steady-state uptake coefficient was γ_av = 2.9 × 10^–9 assuming the BET surface area. Pre-exposing kaolinite to limonene and α-pinene increased O₃ uptake coefficients by nearly 2 orders of magnitude to 2.1 × 10^–7 and 2.5 × 10^–7, respectively. At all humidities studied (10–50% RH), O₃ uptake was at least 1 order of magnitude higher for monoterpene-processed kaolinite compared to that of pure kaolinite. This dramatic increase in O₃ reactivity is attributed to surface-adsorbed organics, namely limonenediol and α-terpineol, which contain alkene functionalities susceptible to ozonolysis. Increasing relative humidity decreased O₃ uptake for monoterpene-processed kaolinite consistent with competitive adsorption of water resulting in lower organic surface concentrations. These results demonstrate the significant impact adsorbed organics can have on O₃ uptake coefficients on mineral aerosol, which should be accounted for in atmospheric modeling studies

Apoptosis of tumor-infiltrating T lymphocytes: a new immune checkpoint mechanism

Immunotherapy based on checkpoint inhibitors is providing substantial clinical benefit, but only to a minority of cancer patients. The current priority is to understand why the majority of patients fail to respond. Besides T-cell dysfunction, T-cell apoptosis was reported in several recent studies as a relevant mechanism of tumoral immune resistance. Several death receptors (Fas, DR3, DR4, DR5, TNFR1) can trigger apoptosis when activated by their respective ligands. In this review, we discuss the immunomodulatory role of the main death receptors and how these are shaping the tumor microenvironment, with a focus on Fas and its ligand. Fas-mediated apoptosis of T cells has long been known as a mechanism allowing the contraction of T-cell responses to prevent immunopathology, a phenomenon known as activation-induced cell death, which is triggered by induction of Fas ligand (FasL) expression on T cells themselves and qualifies as an immune checkpoint mechanism. Recent evidence indicates that other cells in the tumor microenvironment can express FasL and trigger apoptosis of tumor-infiltrating lymphocytes (TIL), including endothelial cells and myeloid-derived suppressor cells. The resulting disappearance of TIL prevents anti-tumor immunity and may in fact contribute to the absence of TIL that is typical of “cold” tumors that fail to respond to immunotherapy. Interfering with the Fas–FasL pathway in the tumor microenvironment has the potential to increase the efficacy of cancer immunotherapy