Aerosol transmission of human pathogens: From miasmata to modern viral pandemics and their preservation potential in the Anthropocene record.

Ongoing uncertainty over the relative importance of aerosol transmission of COVID-19 is in part rooted in the history of medical science and our understanding of how epidemic diseases can spread through human populations. Ancient Greek medical theory held that such illnesses are transmitted by airborne pathogenic emanations containing particulate matter ("miasmata"). Notable Roman and medieval scholars such as Varro, Ibn al-Khatib and Fracastoro developed these ideas, combining them with early germ theory and the concept of contagion. A widely held but vaguely defined belief in toxic miasmatic mists as a dominant causative agent in disease propagation was overtaken by the science of 19th century microbiology and epidemiology, especially in the study of cholera, which was proven to be mainly transmitted by contaminated water. Airborne disease transmission came to be viewed as burdened by a dubious historical reputation and difficult to demonstrate convincingly. A breakthrough came with the classic mid-20th century work of Wells, Riley and Mills who proved how expiratory aerosols (their "droplet nuclei") could transport still-infectious tuberculosis bacteria through ventilation systems. The topic of aerosol transmission of pathogenic respiratory diseases assumed a new dimension with the mid-late 20th century "Great Acceleration" of an increasingly hypermobile human population repeatedly infected by different strains of zoonotic viruses, and has taken centre stage this century in response to outbreaks of new respiratory infections that include coronaviruses. From a geoscience perspective, the consequences of pandemic-status diseases such as COVID-19, produced by viral pathogens utilising aerosols to infect a human population currently approaching 8 billion, are far-reaching and unprecedented. The obvious and sudden impacts on for example waste plastic production, water and air quality and atmospheric chemistry are accelerating human awareness of current environmental challenges. As such, the "anthropause" lockdown enforced by COVID-19 may come to be seen as a harbinger of change great enough to be preserved in the Anthropocene stratal record.

Urban air quality comparison for bus, tram, subway and pedestrian commutes in Barcelona.

Access to detailed comparisons in air quality variations encountered when commuting through a city offers the urban traveller more informed choice on how to minimise personal exposure to inhalable pollutants. In this study we report on an experiment designed to compare atmospheric contaminants inhaled during bus, subway train, tram and walking journeys through the city of Barcelona. Average number concentrations of particles 10-300 nm in size, N, are lowest in the commute using subway trains (N<2.5×10(4) part. cm(-3)), higher during tram travel and suburban walking (2.5×10(4) cm(-3)5.0×10(4) cm(-3)), with extreme transient peaks at busy traffic crossings commonly exceeding 1.0×10(5) cm(-3) and accompanied by peaks in Black Carbon and CO. Subway particles are coarser (mode 90 nm) than in buses, trams or outdoors (<70 nm), and concentrations of fine particulate matter (PM2.5) and Black Carbon are lower in the tram when compared to both bus and subway. CO2 levels in public transport reflect passenger numbers, more than tripling from outdoor levels to >1200 ppm in crowded buses and trains. There are also striking differences in inhalable particle chemistry depending on the route chosen, ranging from aluminosiliceous at roadsides and near pavement works, ferruginous with enhanced Mn, Co, Zn, Sr and Ba in the subway environment, and higher levels of Sb and Cu inside the bus. We graphically display such chemical variations using a ternary diagram to emphasise how "air quality" in the city involves a consideration of both physical and chemical parameters, and is not simply a question of measuring particle number or mass.

A new look at inhalable metalliferous airborne particles on rail subway platforms.

Most particles breathed on rail subway platforms are highly ferruginous (FePM) and extremely small (nanometric to a few microns in size). High magnification observations of particle texture and chemistry on airborne PM10 samples collected from the Barcelona Metro, combined with published experimental work on particle generation by frictional sliding, allow us to propose a general model to explain the origin of most subway FePM. Particle generation occurs by mechanical wear at the brake-wheel and wheel-rail interfaces, where magnetic metallic flakes and splinters are released and undergo progressive atmospheric oxidation from metallic iron to magnetite and maghemite. Flakes of magnetite typically comprise mottled mosaics of octahedral nanocrystals (10-20 nm) that become pseudomorphed by maghemite. Continued oxidation results in extensive alteration of the magnetic nanostructure to more rounded aggregates of non-magnetic hematite nanocrystals, with magnetic precursors (including iron metal) still preserved in some particle cores. Particles derived from steel wheel and rails contain a characteristic trace element chemistry, typically with Mn/Fe=0.01. Flakes released from brakes are chemically very distinctive, depending on the pad composition, being always carbonaceous, commonly barium-rich, and texturally inhomogeneous, with trace elements present in nanominerals incorporated within the crystalline structure. In the studied subway lines of Barcelona at least there appears to be only a minimal aerosol contribution from high temperature processes such as sparking. To date there is no strong evidence that these chemically and texturally complex inhalable metallic materials are any more or less toxic than street-level urban particles, and as with outdoor air, the priority in subway air quality should be to reduce high mass concentrations of aerosol present in some stations.

Natural versus anthropogenic inhalable aerosol chemistry of transboundary East Asian atmospheric outflows into western Japan.

The eastward transport of aerosols exported from mainland Asia strongly influences air quality in the Japanese archipelago. The bulk of the inhalable particulate matter (PM(10)) in these intrusions comprises either natural, desert-derived minerals (mostly supermicron silicates) or anthropogenic pollutants (mostly submicron sulphates), in various states of mixing. We analyse PM(10) collected in Kumamoto, SW Japan, during three contrasting types of aerosol intrusions, the first being dominated by desert PM which became increasingly mixed with anthropogenic components as time progressed, the second being a relatively minor event mixing fine, distal desert PM with anthropogenic materials, and the third being dominated by anthropogenic pollutants. Whereas the chemistry of the natural mineral component is characterised by "crustal" elements (Si, Al, Fe, Mg, K, Li, P, Sc, V, Rb, Sr, Zr, Th, lanthanoids), the anthropogenic component is rich in secondary inorganic compounds and more toxic metallic elements (NH(4)(+), SO(4)(2-), As, Pb, Cd, Cu, Zn, Sn, Bi, Sb, and Ge). Some desert-dust (Kosa) intrusions are more calcareous than others, implicating geologically different source areas, and contain enhanced levels of NO(3)(-), probably as supermicron Ca(NO(3))(2) particles produced by chemical reaction between NOx pollutants (mostly from industry and traffic) and carbonate during atmospheric transport. The overall trace element chemistry of aerosol intrusions into Kumamoto shows low V/Rb, low NO(3)(-)/SO(4)(2-), enhanced As levels, and unfractionated La/Ce values, which are all consistent with anthropogenic sources including coal emissions rather than those derived from the refining and combustion of oil fractionates. Geographically dispersed, residual sulphatic plumes of this nature mix with local traffic (revealed by OC and EC concentrations) and industrial emissions and dissipate only slowly, due to the dominance of submicron accumulation mode PM which is atmospherically persistent, and raise questions over the chronic health effects of breathing finely respirable sulphatic aerosol containing enhanced amounts of toxic metals.

Manganese in the urban atmosphere: identifying anomalous concentrations and sources.

PURPOSE: Industrial emissions can raise urban background levels of inhalable Mn particles in an order of magnitude above normal, eclipsing the contribution made by natural sources and traffic. METHODS: The source of such emissions can be identified using a multidisciplinary approach which integrates ICP-MS chemical analyses of PM(10) and PM(2.5) samples with positive matrix factorization source apportionment modelling, scanning electron microscopy and meteorological data. RESULTS: We apply this methodology to data from Santander (N Spain), where morning Mn-bearing industrial contamination sourcing from the SW is returned towards the city by afternoon NE sea breezes. This wind direction reversal carries the industrial pollution plume inland, detectably raising urban background levels of MnPM(10) in the town of Torrelavega 20 km away. Industrially sourced daily urban background Mn levels at Santander reach >1,000 ng/m(3), average >150 ng/m(3). CONCLUSIONS: We demonstrate the anomalous nature of such concentrations by comparing them with >2,500 PM(10) chemical analyses of ambient PM(10) from other sites in Spain which show how current background Mn levels in urban air typically average only 10 ng/m(3), rising to 20-25 ng/m(3) in city traffic sites. Daily levels of atmospheric Mn PM(10) only rarely exceed 50 ng/m(3), usually during desert dust intrusions which, in extreme cases (such as Canary Islands "calima" events from Africa) can produce Mn concentrations of 100-125 ng/m(3).

Effect of fireworks events on urban background trace metal aerosol concentrations: is the cocktail worth the show?

We report on the effect of a major firework event on urban background atmospheric PM(2.5) chemistry, using 24-h data collected over 8 weeks at two sites in Girona, Spain. The firework pollution episode (Sant Joan fiesta on 23rd June 2008) measured in city centre parkland increased local background PM(2.5) concentrations as follows: Sr (x86), K (x26), Ba (x11), Co (x9), Pb (x7), Cu (x5), Zn (x4), Bi (x4), Mg (x4), Rb (x4), Sb (x3), P (x3), Ga (x2), Mn (x2), As (x2), Ti (x2) and SO(4)(2-) (x2). Marked increases in these elements were also measured outside the park as the pollution cloud drifted over the city centre, and levels of some metals remained elevated above background for days after the event as a reservoir of metalliferous dust persisted within the urban area. Transient high-PM pollution episodes are a proven health hazard, made worse in the case of firework combustion because many of the elements released are both toxic and finely respirable, and because displays commonly take place in an already polluted urban atmosphere.

Variations in vanadium, nickel and lanthanoid element concentrations in urban air.

The emission of trace metal pollutants by industry and transport takes place on a scale large enough to alter atmospheric chemistry and results in measurable differences between the urban background of inhalable particulate matter (PM) in different towns. This is particularly well demonstrated by the technogenic release into the atmosphere of V, Ni, and lanthanoid elements. We compare PM concentrations of these metals in large datasets from five industrial towns in Spain variously influenced by emissions from refinery, power station, shipping, stainless steel, ceramic tiles and brick-making. Increased La/Ce values in urban background inhalable PM, due to La-contamination from refineries and their residual products (fuel oils and petcoke), contrast with Ce-rich emissions from the ceramic related industry, and clearly demonstrate the value of this ratio as a sensitive and reliable tracer for many point source emissions. Similarly, anomalously high V/Ni values (>4) can detect the influence of nearby high-V petcoke and fuel oil combustion, although the use of this ratio in urban background PM is limited by overlapping values in natural and anthropogenic materials. Geochemical characterisation of urban background PM is a valuable compliment to the physical monitoring of aerosols widely employed in urban areas, especially given the relevance of trace metal inhalation to urban health issues.

Identification of chemical tracers in the characterisation and source apportionment of inhalable inorganic airborne particles: an overview.

The acquisition of increasingly large analytical datasets from standardized air pollution monitoring stations allows more effective characterization of the fine aerosol cocktail breathed daily by modern urban populations. It is increasingly clear from such data that there is great variability in the chemical composition of inorganic inhalable particulate matter (PM10 = < 10 microm in size) in both space and time. Such variability can be demonstrated using selected tracer elements which, combined with source apportionment techniques, allow differentiation between natural (geological) and anthropogenic sources such as traffic and various industries. These tracer elements, which are commonly toxic metals, can be shown to concentrate in the finer, more deeply inhalable PM fraction, and are thus linked to potential inflammation and oxidative stress after inhalation. Legislation concerned only with measuring physical PM mass concentrations therefore fails to address potential health effects linked to chemical variations in ambient aerosols.

Lanthanoid geochemistry of urban atmospheric particulate matter.

Relatively little is known about the lanthanoid element (La to Lu) chemistry of inhalable urban atmospheric particulate matter (PM). PM samples collected during an air sampling campaign in the Mexico City area contain lanthanoid concentrations of mostly 1-10 ng m(-3), increasing with mass where resuspension of crustal PM is important (low PM2.5/PM10), but not where fine emissions from traffic and industry dominate (high PM2.5/ PM10). Samples show anthropogenic enrichment of lighter over heavier lanthanoids, and Ce enrichment relative to La and Sm occurs in the city center (especially PM10) possibly due to PM from road vehicle catalytic converters. La is especially enriched, although many samples show low La/V values (< 0.11), suggesting the dominating influence of fuel oil combustion sources rather than refinery emissions. We use La/Sm v La/ Ce, LaCeSm, and LaCeV plots to compare Mexico City aerosols with PM from other cities. Lanthanoid aerosol geochemistry can be used not only to identify refinery pollution events, but also as a marker for different hydrocarbon combustion emissions (e.g., oil or coal power stations) on urban background atmospheric PM.

Airborne particulate matter and premature deaths in urban Europe: the new WHO guidelines and the challenge ahead as illustrated by Spain.

Twenty first century epidemiological publications on urban air pollution are confirming that inhalation of fine, airborne particulate matter (PM) has serious chronic human health effects and is a major cause of premature death worldwide. Recently updated recommendations by WHO identify three "Interim Targets" for the stepped reduction in PM levels within world cities in the quest to achieve an annual mean Air Quality Guideline (AQG) concentration of 20 mug/m(3) for particles less than 10 microns in size (PM(10)). In this paper we offer a perspective from Spain, a country with the longest record of reporting pollution data from large numbers of urban traffic sites to a central European database (AIRBASE). We can demonstrate that average annual PM concentrations at urban traffic monitoring stations in many European cities continue to be 50-100% above the WHO AQG, a situation exacerbated by high urban PM(2.5/10) ratios which indicate a dominance of finer, more deeply inhalable particles potentially more detrimental to health. Given that WHO has estimated in 2000 there were well over 250,000 premature deaths in Europe attributable to PM inhalation, such continuing high urban pollution levels are placing a huge burden on European medical resources.

Geochemical variations in aeolian mineral particles from the Sahara-Sahel Dust Corridor.

The Sahara-Sahel Dust Corridor runs from Chad to Mauritania and expels huge amounts of mineral aerosols into the Atlantic Ocean. Data on samples collected from Algeria, Chad, Niger, and Western Sahara illustrate how corridor dust mineralogy and chemistry relate to geological source and weathering/transport history. Dusts sourced directly from igneous and metamorphic massifs are geochemically immature, retaining soluble cations (e.g., K, Na, Rb, Sr) and accessory minerals containing HFSE (e.g., Zr, Hf, U, Th) and REE. In contrast, silicate dust chemistry in desert basins (e.g., Bodélé Depression) is influenced by a longer history of transport, physical winnowing (e.g., loss of Zr, Hf, Th), chemical leaching (e.g., loss of Na, K, Rb), and mixing with intrabasinal materials such as diatoms and evaporitic salts. Mineral aerosols blown along the corridor by the winter Harmattan winds mix these basinal and basement materials. Dusts blown into the corridor from sub-Saharan Africa during the summer monsoon source from deeply chemically weathered terrains and are therefore likely to be more kaolinitic and stripped of mobile elements (e.g., Na, K, Mg, Ca, LILE), but retain immobile and resistant elements (e.g., Zr, Hf, REE). Finally, dusts blown southwestwards into the corridor from along the Atlantic Coastal Basin will be enriched in carbonate from Mesozoic-Cenozoic marine limestones, depleted in Th, Nb, and Ta, and locally contaminated by uranium-bearing phosphate deposits.

PM source apportionment and trace metallic aerosol affinities during atmospheric pollution episodes: a case study from Puertollano, Spain.

Source apportionment study was performed, applying principal component analysis to the results of 221 chemical analyses of PM10 and PM2.5 samples collected daily from the industrial (but low traffic) Spanish town of Puertollano over a 14-month period during 2004-2005. Results reveal compositional variations attributable to different mixtures of natural and anthropogenic materials, mainly soil and rock dust (crustal), marine salt (only in PM10), petrochemical refinery emissions, and particles attributed to the combustion of local coal, which is unusually rich in Pb and Sb. During the study period there were 34 pollution episodes when PM10 exceeded 50 tg m(-3), mostly due to winter air temperature inversions, regional atmospheric stagnation, or African dust incursions (North African, NAF days: usually in summer). Whereas the crustal component during NAF episodes averaged 52% with a PM2.5/PM10 ratio of 0.54, this dropped to 29% and a PM2.5/PM10 of 0.67 during non-NAF days when anthropogenic materials predominated. Abnormally enhanced concentrations of pathfinder metallic trace elements provide additional evidence for source apportionment: thus aerosols with raised levels of Pb and Sb are associated with local coal combustion, Ni and V can be linked to petrochemical PM emissions, and Ti, Mn, Rb, and Ce are particularly characteristic of crustal dust incursions.

Variations in the source, metal content and bioreactivity of technogenic aerosols: a case study from Port Talbot, Wales, UK.

Atmospheric aerosol samples were collected during different prevailing wind directions from a site located close to a busy motorway, a major steelworks, and the town of Port Talbot (Wales, UK). A high-volume collector was used (1100 l/min), enabling relatively large amounts of particulate matter (PM(10-2.5) and PM(2.5)) samples to be obtained on a polyurethane foam [PUF, H(2)N-C(O)O-CH(2)CH(3)] substrate over periods of 2-7 days. Four samples were chosen to exemplify different particle mixtures: SE- and NE-derived samples for particles moving along and across the motorway, a NW-derived sample from the town, and a mixed SW/SE-derived sample containing a mixture of particles from both steelworks and motorway. The latter sample showed the highest average collection rate (0.9 mg/h, 13 microg/m(3)) and included a prominent pollution episode when rainy winds were blowing from the direction of the steelworks. Both NW and SE samples were collected under dry conditions and show the same collection rate (0.7 mg/h, 10 microg/m(3)), whereas the NE sample was collected during wetter weather and shows the lowest rate (0.3 mg/h, 5 microg/m(3)). Scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis system (EDX) analyses show all samples are dominated by elemental and organic carbon compounds (EOCC) and nitrates, with lesser amounts of sulphates, felsic silicates, chlorides and metals. ICP-MS analyses show the SW/SE sample to be richest in metals, especially Fe, Zn, Ni, and Mn, these being attributed to an origin from the steelworks. The SE sample, blown along the motorway corridor, shows enhanced levels of Pb, V, Ti, As, and Ce, these metals being interpreted as defining a traffic-related chemical fingerprint. The NW sample shows a very low metal content. DNA plasmid assay data on the samples show TM(50) values varying from 66 to 175 microg/ml for the adjusted whole sample and 89 to 203 microg/ml for the soluble fraction. The SW/SE-mixed metalliferous sample is the most bioreactive (both whole and soluble) and the soluble fraction of the metal-depleted NW sample is the least bioreactive. The metal content of the aerosol samples, especially soluble metals such as Zn, is suggested to be the primary component responsible for oxidative damage of the DNA, and therefore most implicated in any health effects arising from the inhalation of these particulate cocktails.