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Abstract. Ambient air pollution poses a significant threat to public health, particularly in low and middle-income countries, where detailed data on particulate matter (PM) mass and composition are scarce. We conducted a year-long study on PM composition and sources in Eastern Africa (Kigali, Rwanda). The annual mean concentration of PM1 was 31±15µgm-3 , with slightly higher concentrations during the dry season. Organic aerosols (OA) contributed 73 % of the observed PM1 mass, black carbon (BC) 16 %, nitrate 6 %, sulfate and ammonium 2 % each, and chlorine 1 %. BC is approximately 60 % due to fossil fuel emissions and 40 % from biomass burning emissions. Tracer ions detected by the aerosol mass spectrometer suggest that photochemistry plays a significant role in the formation of secondary OA during the daytime (06:00 a.m.–06:00 p.m.), while primary OA dominates in the morning and evening due to increased anthropogenic activity and shallower boundary layer height. PM1 OA in Kigali is primarily composed of Oxygenated Organic Aerosols (OOA, 45 %), Hydrocarbon-like OA (HOA, 32 %), and Biomass Burning OA (BBOA, 23 %). Secondary organic aerosol (SOA) accounted for 47 % and 41 % of PM1 OA during the rainy and dry seasons, while primary OA (POA: BBOA + HOA) contributed 53 % and 59 %. Short-term interventions that limit traffic activity on some Saturdays and Sundays had a mixed impact on ambient PM1 and PM2.5 concentrations, with car-free Sundays reducing PM1 concentrations throughout most of the day. 

Asphalt-related emissions are an understudied source of reactive organic compounds with the potential to form organic aerosol (OA). Ambient aerosol mass spectrometry (AMS) measurements of asphalt-related aerosols near a month-long road paving project showed enhanced ambient OA concentrations with a mix of primary and secondary OA signatures. For comparison, gas-phase emissions from real-world road asphalt samples at application (e.g., 140 °C) and in-use (e.g., 60 °C) temperatures were injected into an environmental chamber and an oxidation flow reactor to simulate varying degrees of oxidative aging while measuring their gas- and aerosol-phase oxidation products. Secondary OA formation was observed via both self-nucleation and condensation, with chemical properties dependent on asphalt temperature and reaction conditions. The chemical composition of less-aged asphalt-related OA observed in outdoor and laboratory measurements was similar to OA from other petrochemical-based sources and hydrocarbon-like OA source factors observed via AMS in previous urban studies. The composition of aged OA varied with the degree of oxidation, similar to oxidized OA factors observed in ambient air. Taken together, these field and laboratory observations suggest that contributions to urban OA during and after application may be challenging to deconvolve from other traditional sources in ambient measurements. 

Abstract. Cooking is an important but understudied source of urban anthropogenic fine particulate matter (PM2.5). Using a mobile laboratory, we measured PM size and composition in urban restaurant plumes. Size distribution measurements indicate that restaurants are a source of urban ultrafine particles (UFPs, particles <100 nm mobility diameter), with a mode diameter <50 nm across sampled restaurants and particle number concentrations (PNCs, a proxy for UFPs) that were substantially elevated relative to the urban background. In our observations, PM mass emitted from restaurants was almost entirely organic aerosol (OA). Aerosol mass spectra show that while emissions from most restaurants were similar, there were key mass spectral differences. All restaurants emit OA at m/z 41, 43, and 55, though the composition (e.g., the ratio of oxygenated to reduced ions at specific m/z) varied across locations. All restaurant emissions included reduced-nitrogen species detected as CxHyN+ fragments, making up ∼15 % of OA mass measured in plumes, with reduced molecular functionalities (e.g., amines, imides) that were often accompanied by oxygen-containing functional groups. The largest reduced-nitrogen emissions were observed from a commercial bread bakery (i.e., 30 %–50 % of OA mass), highlighting the marked differences between restaurants and their importance for emissions of both urban UFPs and reduced nitrogen. 

Metabolic adaptations are essential for survival. The mitochondrial calcium uniporter plays a key role in coordinating metabolic homeostasis by regulating mitochondrial metabolic pathways and calcium signaling. However, a comprehensive analysis of uniporter-regulated mitochondrial pathways has remained unexplored. Here, we investigate consequences of uniporter loss and gain of function using uniporter knockout cells and fibrolamellar carcinoma (FLC), which we demonstrate to have elevated mitochondrial calcium levels. We find that branched-chain amino acid (BCAA) catabolism and the urea cycle are uniporter-regulated pathways. Reduced uniporter function boosts expression of BCAA catabolism genes and the urea cycle enzyme ornithine transcarbamylase. In contrast, high uniporter activity in FLC suppresses their expression. This suppression is mediated by the transcription factor KLF15, a master regulator of liver metabolism. Thus, the uniporter plays a central role in FLC-associated metabolic changes, including hyperammonemia. Our study identifies an important role for the uniporter in metabolic adaptation through transcriptional regulation of metabolism and elucidates its importance for BCAA and ammonia metabolism. 

Our method measures atmospheric BC concentrations by analyzing photos of particle deposits on glass-fiber filters. Post-analysis of beta attenuation monitor (BAM) tapes collected worldwide can be a valuable source for hourly BC data, particularly for Global South countries. 

ABSTRACT NGC 6302 is a spectacular bipolar planetary nebula (PN) whose spectrum exhibits fast outflows and highly ionized emission lines, indicating the presence of a very hot central star ($${\sim}$$220 000 K). Its infrared spectrum reveals a mixed oxygen and carbon dust chemistry, displaying both silicate and polycyclic aromatic hydrocarbon (PAH) features. Using the James Webb Space Telescope Mid-Infrared Instrument and Medium Resolution Spectrometer, a mosaic map was obtained over the core of NGC 6302, covering the wavelength range of 5–28 $$\mu$$m and spanning an area of $${\sim}$$18.5 arcsec $$\times$$ 15arcsec. The spatially resolved spectrum reveals $${\sim}$$200 molecular and ionized lines from species requiring ionization potentials of up to 205 eV. The spatial distributions highlight a complex structure at the nebula’s centre. Highly ionized species such as [Mg vii] and [Si vii] show compact structures, while lower ionization species such as H$^+$ extend much farther outwards, forming filament-defined rims that delineate a bubble. Within the bubble, the H$^+$ and H$$_2$$ emission coincide, while the PAH emission appears farther out, indicating an ionization structure distinct from typical photodissociation regions, such as the Orion Bar. This may be the first identification of a PAH formation site in a PN. This PN appears to be shaped not by a steady, continuous outflow, but by a series of dynamic, impulsive bubble ejections, creating local conditions conducive to PAH formation. A dusty torus surrounds the core, primarily composed of large ($$\mu$$m-sized) silicate grains with crystalline components. The long-lived torus contains a substantial mass of material, which could support an equilibrium chemistry and a slow dust-formation process.