HOx cycling during the Cyprus Photochemistry Experiment

Meeting abstract fro AOGS 2016 Beijing for an oral presentation of results from the CYPHEX 2014 measurement campaign.Abstract from attachedMax Planck Society, University of Cheste

Interactions between biosphere and atmosphere as an important source of nitrous acid

Interactions between biosphere, lithosphere, hydrosphere and atmosphere are important processes in the Earth´s environment. There are several elements which are distributed in each compartment, e.g., nitrogen and carbon. Biogeochemical cycles describe the partition and the pathways of those compounds between environmental compartments. In this PhD project the partition of nitrous acid between the lithosphere/biosphere and atmosphere has been studied. Nitrous acid (HONO) is not only part of the nitrogen cycle, but also an important precursor of the OH radical, the key oxidant in the atmosphere. The current knowledge of atmospheric HONO sources is still unsatisfactory. Thus, more research on HONO sources is needed to improve simulations of the oxidative capacity of the atmosphere. One main focus of this work is on biological emissions of reactive nitrogen (HONO and NO) from soil and biological soil crusts which cover the soil surface in semi-arid regions. The PhD study shows that natural ground surface emission can be the major source of atmospheric HONO in rural/remote regions. This was indicated by field measurements in Cyprus, a rural island in the East Mediterranean Sea, which detected much higher daytime HONO concentrations than expected by budget analysis and photostationary state calculations. While observed NO2 concentrations were low, demonstrating that heterogeneous NO2 conversion couldn´t account significantly for the HONO budget, the missing HONO source correlated well with NO and its missing source indicating a common origin. Laboratory based measurements of reactive nitrogen emission from local soil and biological soil crust samples (chlorolichen-, moss- and cyanobacteria-dominated types) showed a wide range of emission rates, which extrapolation, nevertheless, revealed a share of ~75% of the unaccounted HONO source. On the other hand, only 8% of the missing NO source could be attributed to soil/crust emissions and the NO source remained unclear. Although the low NO2 concentrations observed in Cyprus are not sufficient to explain the missing HONO source by heterogeneous uptake and conversion, the unexpected high HONO to NOx ratio (mean 0.33) may indicate a highly efficient pathway to convert NO2 into HONO. In addition, the good correlation of the missing HONO source with the product of the NO2 photolysis rate and ambient NO2 concentrations suggests photo-induced HONO formation. Hence, light enhanced heterogeneous conversion of NO2 on biological surfaces, using proteins as a proxy, was studied in detail. Proteins exposed to NO2 and light were shown to be nitrated and decompose, accompanied by simultaneous HONO production. Nitration of proteins enhances their allergenic potential. Initial NO2 uptake coefficients on bovine serum albumin are comparable with NO2 uptake coefficients reported for other surfaces like humic acid, several aromatic compounds or soot. Unlike in other studies, persistent HONO formation over a long time was observed, indicative of a catalytic surface reactivity. In conclusion, the biosphere can play an important role in the atmospheric HONO budget, either by biological production and subsequent emission or by acting as a reactive surface for heterogeneous NO2 conversion.Wechselwirkungen zwischen Biosphäre, Lithosphäre, Hydrosphäre und Atmosphäre sind wichtige Prozesse in der Umwelt der Erde. Es gibt einige Elemente, wie z.B. Stickstoff und Kohlenstoff, die in jedem dieser Bereiche vorkommen. Biogeochemische Kreisläufe beschreiben die Verteilung und die Pfade solcher Stoffe zwischen den Umweltbereichen. In dieser Doktorarbeit wird die Verteilung von salpetriger Säure zwischen Lithosphäre/ Biosphäre und Atmosphäre untersucht. Salpetrige Säure (HONO) ist nicht nur Teil des Stickstoffkreislaufs sondern auch ein wichtiger Vorläufer des OH Radikals, des Hauptoxidationsmittels in der Atmosphäre. Der derzeitige Wissensstand über atmosphärische HONO Quellen ist noch ungenügend. Demzufolge sind weitere Untersuchungen von HONO Quellen nötig um das Oxidationsvermögen der Atmosphäre besser simulieren zu können. Ein Schwerpunkt dieser Doktorarbeit liegt bei der Untersuchung biologischer Emissionen von reaktivem Stickstoff (HONO und NO) aus Böden und biologischen Bodenkrusten, die die Bodenoberfläche in semiariden Regionen bedecken. Die Doktorarbeit zeigt, dass Emissionen aus natürlichen Bodenoberflächen die Hauptquelle von atmosphärischem HONO in ländlichen oder abgeschiedenen Gegenden sein können. Dies wurde anhand von Feldmessungen auf Zypern, einer ländlichen geprägten Insel im östlichen Mittelmeer gezeigt, welche viel höhere HONO-Tageskonzentrationen detektierten als durch Budgetanalysen und photostationäre Gleichgewichtsberechnungen zu erwarten waren. Während beobachtete NO2 Konzentrationen gering waren und folglich heterogene NO2 Umwandlungen nicht bedeutend zum HONO Budget beitragen konnten, korrelierte die fehlende HONO Quelle mit NO und dessen fehlender Quelle, was auf einen gemeinsamen Ursprung hindeutete. Laborbasierte Emissionsmessungen von reaktivem Stickstoff aus lokalen Boden- und biologischen Bodenkrustenproben (Grünalgenflechten, Moose und Cyanobakterien dominierende Typen) ergaben eine große Spanne an Emissionsraten, deren Hochrechnung dennoch einen Anteil von etwa 75% der fehlenden HONO Quelle abdeckten. Anderseits konnten nur 8% der fehlenden NO Quelle den Boden-und Bodenkrustenemissionen zugeschrieben werden und die NO Quelle blieb unklar. Obwohl die geringen NO2 Konzentrationen, die in Zypern beobachtet wurden, nicht ausreichten um die fehlende HONO Quelle durch heterogene Aufnahme und Umsetzung zu erklären, könnte das unerwartet hohe HONO-NOx-Verhältnis (im Mittel 0.33) auf einen sehr effizienten Weg zur Umwandlung von NO2 zu HONO hinweisen. Zusätzlich deutet die gute Korrelation von der fehlenden HONO Quelle mit dem Produkt aus der NO2 Photolyserate und der NO2-Umgebungskonzentration auf eine durch Licht initiierte HONO Bildung. Folglich wurde die durch Licht verstärkte heterogene NO2-Umwandlung an Proteinen, stellvertretend für biologische Oberflächen, genauer untersucht. Es wurde gezeigt, dass Proteine, die NO2 und Licht ausgesetzt sind, nitriert und unter gleichzeitiger HONO Bildung abgebaut werden. Nitrierung von Proteinen verstärkt deren Potential Allergien auszulösen. Anfängliche NO2 Aufnahmekoeffizienten von Rinderserumalbumin sind mit berichteten NO2 Aufnahmekoeffizienten von verschiedenen Oberflächen wie Huminsäure, einige aromatische Verbindungen oder Ruß vergleichbar. Anders als in anderen Studien, wurde eine stabile HONO Bildung über einen langen Zeitraum beobachtet, was auf eine katalytische Oberflächenaktivität hinweist. Schlussfolgernd kann die Biosphäre, entweder durch biologische Produktion und folgender Emission oder durch Bereitstellung einer reaktiven Oberfläche für NO2 Umwandlung, eine wichtige Rolle im atmosphärischem HONO-Budget spielen

Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) in the environment – A review

Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) are derivatives of PAHs with at least one nitro-functional group (-NO2) on the aromatic ring. The toxic effects of several nitro-PAHs are more pronounced than those of PAHs. Some nitro-PAHs are classified as possible or probable human carcinogens by the International Agency for Research on Cancer. Nitro-PAHs are released into the environment from combustion of carbonaceous materials (e.g. fossil fuels, biomass, waste) and post-emission transformation of PAHs. Most studies on nitro-PAHs are about air (gas-phase and particulate matter), therefore less is known about the occurrence, concentrations, transport and fate of nitro-PAHs in soils, aquatic environment and biota. Studies on partition and exchange of nitro-PAHs between adjacent environmental compartments are also sparse. The concentrations of nitro-PAHs cannot easily be predicted from the intensity of anthropogenic activity or easily related to those of PAHs. This is because anthropogenic source strengths of nitro-PAHs are different from those of PAHs, and also nitro-PAHs have additional sources (formed by photochemical conversion of PAHs). The fate and transport of nitro-PAHs could be considerably different from their related PAHs because of their higher molecular weights and considerably different sorption mechanisms. Hence, specific knowledge on nitro-PAHs is required. Regulations on nitro-PAHs are also lacking. We present an extensive review of published literature on the sources, formation, physico-chemical properties, methods of determination, occurrence, concentration, transport, fate, (eco)toxicological and adverse health effects of nitro-PAHs. We also make suggestions and recommendations about data needs, and future research directions on nitro-PAHs. It is expected that this review will stimulate scientific discussion and provide the basis for further research and regulations on nitro-PAHs

Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) in the environment – A review

Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) are derivatives of PAHs with at least one nitro-functional group (-NO2) on the aromatic ring. The toxic effects of several nitro-PAHs are more pronounced than those of PAHs. Some nitro-PAHs are classified as possible or probable human carcinogens by the International Agency for Research on Cancer. Nitro-PAHs are released into the environment from combustion of carbonaceous materials (e.g. fossil fuels, biomass, waste) and post-emission transformation of PAHs. Most studies on nitro-PAHs are about air (gas-phase and particulate matter), therefore less is known about the occurrence, concentrations, transport and fate of nitro-PAHs in soils, aquatic environment and biota. Studies on partition and exchange of nitro-PAHs between adjacent environmental compartments are also sparse. The concentrations of nitro-PAHs cannot easily be predicted from the intensity of anthropogenic activity or easily related to those of PAHs. This is because anthropogenic source strengths of nitro-PAHs are different from those of PAHs, and also nitro-PAHs have additional sources (formed by photochemical conversion of PAHs). The fate and transport of nitro-PAHs could be considerably different from their related PAHs because of their higher molecular weights and considerably different sorption mechanisms. Hence, specific knowledge on nitro-PAHs is required. Regulations on nitro-PAHs are also lacking. We present an extensive review of published literature on the sources, formation, physico-chemical properties, methods of determination, occurrence, concentration, transport, fate, (eco)toxicological and adverse health effects of nitro-PAHs. We also make suggestions and recommendations about data needs, and future research directions on nitro-PAHs. It is expected that this review will stimulate scientific discussion and provide the basis for further research and regulations on nitro-PAHs

Azaarenes in fine particulate matter from the atmosphere of a Chinese megacity

Azaarenes (AZAs) are toxicologically relevant organic compounds with physicochemical properties that are significantly different from the well-studied polycyclic aromatic hydrocarbons (PAHs). However, little is known about their concentrations, seasonal variations, fate, and relationship with PAHs in air. This paper reports the temporal variations in the concentrations and composition patterns of AZAs in PM2.5 that was sampled once per 6 days from outdoor air of Xi'an, China from July 2008 to August 2009. The concentrations of the aAZAs, quinoline (QUI), benzo[h]quinoline (BQI), and acridine (ACR) in PM2.5 were 213-6441, 185-520, 69-2483, and 10-3544 pg m(-3), respectively. These concentrations were higher than those measured in urban areas of Western Europe. AZA compositional patterns were dominated by BQI and ACR. The high concentration of AZAs, high AZA/related PAH ratio, and the dominance of three-ring AZAs (BQI and ACR) in PM2.5 of Xi'an are all in contrast to observations from Western European and North American cities. This contrast likely reflects differences in coal type and the more intense use of coal in China. The PM2.5-bound concentration of AZA in winter season (W) was higher than during the summer season (S) with W/S ratios of 5.7, 1.4, 4.1, and 13, for aAZAs, QUI, BQI, and ACR, respectively. Despite their significantly different physicochemical properties, AZAs were significantly (p < 0.05) positively correlated with their related PAHs and pyrogenic elemental carbon. The changes in AZA concentrations were positively correlated with ambient pressure but negatively correlated with ambient temperature, wind speed, and relative humidity. This trend is similar to that observed for the related PAHs. We conclude that Xi'an and possibly other Chinese cities have higher emission of AZAs into their atmosphere because of the more pronounced use of coal. We also conclude that in spite of differences in physicochemical properties between AZAs and related PAHs, the atmospheric dynamics and relationships with meteorological factors of both compound groups are similar

PM2.5-bound oxygenated PAHs, nitro-PAHs and parent-PAHs from the atmosphere of a Chinese megacity: seasonal variation, sources and cancer risk assessment

Polycyclic aromatic compounds (PACs) in air particulate matter contribute considerably to the health risk of air pollution. The objectives of this study were to assess the occurrence and variation in concentrations and sources of PM2.5-bound PACs [Oxygenated PAHs (OPAHs), nitro-PAHs and parent-PAHs] sampled from the atmosphere of a typical Chinese megacity (Xi'an), to study the influence of meteorological conditions on PACs and to estimate the lifetime excess cancer risk to the residents of Xi'an (from inhalation of PM2.5-bound PACs). To achieve these objectives, we sampled 24-h PM2.5 aerosols (once in every 6 days, from 5 July 2008 to 8 August 2009) from the atmosphere of Xi'an and measured the concentrations of PACs in them. The PM2.5-bound concentrations of Σcarbonyl-OPAHs, ∑ hydroxyl + carboxyl-OPAHs, Σnitro-PAHs and Σalkyl + parent-PAHs ranged between 5–22, 0.2–13, 0.3–7, and 7–387 ng m− 3, respectively, being markedly higher than in most western cities. This represented a range of 0.01–0.4% and 0.002–0.06% of the mass of organic C in PM2.5 and the total mass of PM2.5, respectively. The sums of the concentrations of each compound group had winter-to-summer ratios ranging from 3 to 8 and most individual OPAHs and nitro-PAHs had higher concentrations in winter than in summer, suggesting a dominant influence of emissions from household heating and winter meteorological conditions. Ambient temperature, air pressure, and wind speed explained a large part of the temporal variation in PACs concentrations. The lifetime excess cancer risk from inhalation (attributable to selected PAHs and nitro-PAHs) was six fold higher in winter (averaging 1450 persons per million residents of Xi'an) than in summer. Our results call for the development of emission control measures

Protein Cross-Linking and Oligomerization through Dityrosine Formation upon Exposure to Ozone.

Air pollution is a potential driver for the increasing prevalence of allergic disease, and post-translational modification by air pollutants can enhance the allergenic potential of proteins. Here, the kinetics and mechanism of protein oligomerization upon ozone (O3) exposure were studied in coated-wall flow tube experiments at environmentally relevant O3 concentrations, relative humidities and protein phase states (amorphous solid, semisolid, and liquid). We observed the formation of protein dimers, trimers, and higher oligomers, and attribute the cross-linking to the formation of covalent intermolecular dityrosine species. The oligomerization proceeds fast on the surface of protein films. In the bulk material, reaction rates are limited by diffusion depending on phase state and humidity. From the experimental data, we derive a chemical mechanism and rate equations for a kinetic multilayer model of surface and bulk reaction enabling the prediction of oligomer formation. Increasing levels of tropospheric O3 in the Anthropocene may promote the formation of protein oligomers with enhanced allergenicity and may thus contribute to the increasing prevalence of allergies

Light-induced protein nitration and degradation with HONO emission

Proteins can be nitrated by air pollutants (NO2), enhancing their allergenic potential. This work provides insight into protein nitration and subsequent decomposition in the presence of solar radiation. We also investigated light-induced formation of nitrous acid (HONO) from protein surfaces that were nitrated either online with instantaneous gas-phase exposure to NO2 or offline by an efficient nitration agent (tetranitromethane, TNM). Bovine serum albumin (BSA) and ovalbumin (OVA) were used as model substances for proteins. Nitration degrees of about 1% were derived applying NO2 concentrations of 100 ppb under VIS=UV illuminated conditions, while simultaneous decomposition of (nitrated) proteins was also found during long-term (20 h) irradiation exposure. Measurements of gas exchange on TNM-nitrated proteins revealed that HONO can be formed and released even without contribution of instantaneous heterogeneous NO2 conversion. NO2 exposure was found to increase HONO emissions substantially. In particular, a strong dependence of HONO emissions on light intensity, relative humidity, NO2 concentrations and the applied coating thickness was found. The 20 h long-term studies revealed sustained HONO formation, even when concentrations of the intact (nitrated) proteins were too low to be detected after the gas exchange measurements. A reaction mechanism for the NO2 conversion based on the Langmuir–Hinshelwood kinetics is proposed