Microplastic atmospheric pollution in an urban Southern Brazil region: What can spider webs tell us?

The World Health Organization categorizes air pollution as the presence of one or more contaminants in the atmosphere such as smoke, dust, and particulate matter like microplastics, which are considered a priority pollutant. However, only a few studies have been developed on atmospheric pollution, and knowledge about MPs in the atmosphere is still limited. Spider webs have been tested and used as a passive sampling approach to study anthropogenic pollution. Despite this, studies on microplastic contamination using spiderwebs as samplers are scarce. Thus, this study uses spider webs as passive indicators to investigate air quality regarding microplastic contamination in an urbanized area. Therefore, 30 sampling points were selected, and webs of Nephilingis cruentata were collected. The spider webs were dipped in KOH 10 %. After digestion, the solution was washed and sieved through a 90 µm geological sieve. The remaining material was transferred to a Petri dish with filter paper, quantified, and identified by type and color. The chemical composition of the polymers was determined using Raman spectroscopy. 3138 microplastics were identified (2973 filaments and 165 fragments). The most frequent colors were blue and black. Raman spectroscopy revealed five types of polymers: Isotactic Polypropylene, Polyethylene Terephthalate, Polyurethane, Polyamide, and Direct Polyethylene.

Primary and secondary organic winter aerosols in Mediterranean cities under different mixing layer conditions (Barcelona and Granada).

PM10 was collected during an EMEP winter campaign of 2017-2018 in two urban background sites in Barcelona (BCN) and Granada (GRA), two Mediterranean cities in the coast and inland, respectively. The concentrations of PM10, organic carbon (OC), elemental carbon (EC), and organic molecular tracer compounds such as hopanes, anhydro-saccharides, polycyclic aromatic hydrocarbon, and several biogenic and anthropogenic markers of secondary organic aerosols (SOA) were two times higher in GRA compared to BCN and related to the atmospheric mixing heights in the areas. Multivariate curve resolution (MCR-ALS) source apportionment analysis identified primary emissions sources (traffic + biomass burning) that were responsible for the 50% and 20% of the organic aerosol contributions in Granada and Barcelona, respectively. The contribution of biomass burning was higher in the holidays than in the working days in GRA while all primary combustion emissions decreased in holidays in BCN. The MCR-ALS identified that oxidative species and SOA formation processes contributed to 40% and 80% in Granada and Barcelona, respectively. Aged SOA was dominant in Granada and Barcelona under stagnant atmospheric conditions and in presence of air pollution. On the other hand, fresh SOA contributions from α-pinene oxidation (cis-pinonic acid) were three times higher in Barcelona than Granada and could be related to new particle formation, essentially due to overall cleaner air conditions and elevated air temperatures.

The removal of PM2.5 by trees in tropical Andean metropolitan areas: an assessment of environmental change scenarios.

Metropolitan areas in Andean industrialized valleys with a strong geomorphological structure and a pronounced climate experience an increasing degradation of air quality, which motivates environmental policies that include the expansion of tree coverage in urban areas among the mitigation measures. Using the metropolitan area of the Aburrá Valley, Colombia, as a study case, we evaluate the removal of PM2.5 by urban trees with the Urban Forest Effects (UFORE) methodology, considering the potential effect of changing tree covers in the valley for several projected meteorological conditions under climate change and different urban management practices. The estimated removals are sensitive to the number and distribution of available ground stations, with a tendency to overestimate with fewer stations. We found that the marginal gains in removal by additional tree plantings are low in the urbanized settings. In the environmental scenarios, the main limiting factor in the removal is precipitation, compared to changes in tree cover and levels of pollution. Spatially, the increase in total removal depends on the increase in tree cover, with more benefits obtained when trees are in areas with high concentrations of PM2.5. Trees with low values of leaf area index (LAI) seem to optimize the effectiveness of the removal. Seasonally, the greatest removal occurs in rainy months when pollution levels are the highest. Based on our results, the scenarios that meet the plans and programs aimed at improving air quality would achieve removal effectiveness of around 2.5% of the total emissions of PM2.5 with urban trees. Air quality would achieve removal effectiveness of around 2.5% of the total emissions of PM2.5 with urban trees.

Air pollution and COVID-19 lockdown in a large South American city: Santiago Metropolitan Area, Chile.

The implementation of confinement and physical distancing measures to restrict people's activities and transit in the midst of the COVID-19 pandemic allowed us to study how these measures affect the air quality in urban areas with high pollution rates, such as Santiago, Chile. A comparative study between the concentrations of PM10, PM2.5, NOx, CO, and O3 during the months of March to May 2020 and the corresponding concentrations during the same period in 2017-2019 is presented. A combination of surface measurements from the air quality monitoring network of the city, remote satellite measurements, and simulations of traffic activity and road transport emissions allowed us to quantify the change in the average concentrations of each pollutant. Average relative changes of traffic emissions (between 61% and 68%) implied statistically significant concentrations reductions of 54%, 13%, and 11% for NOx, CO, and PM2.5, respectively, during the pandemic period compared to historical period. In contrast, the average concentration of O3 increased by 63% during 2020 compared to 2017-2019. The nonlinear response observed in the pollution levels can be attributed to the changes in the vehicular emission patterns during the pandemic and to the role of other sources such as residential emissions or secondary PM.

Ambient particulate matter in Santiago, Chile: 1989-2018: A tale of two size fractions.

We have analyzed trends in ambient fine (PM2.5) and coarse (PM2.5-10) particulate matter in Santiago, Chile, for the last 30 years. PM2.5 has monotonously decreased between 67% and 72% at those sites. Trends varied between -2.0 and -2.7 (µg/m3/year) between 1989 and late 90's, and between -0.7 and -1.1 (µg/m3/year) afterwards. This slowing down is likely a consequence of fast increase of motor vehicles in the city, which have become a dominant source of ambient PM2.5. Annual ambient PM2.5 concentrations are still above 20 (µg/m3), so more regulation is needed to bring them down. Coarse particles have changed little in 30 years, decreasing between 0% and 12%; particle concentrations have evolved in a non-linear way: first increasing in 1989-1995, then decreasing until 2003, and with a flat trend afterwards. We ascribe these trends to a combination of a) public works implemented throughout the city, b) fugitive dust controls like street sweeping programs and emission offsets for PM10 and c) increasing numbers of motor vehicles in the city. Further initiatives are needed to curb down coarse particles as well. By considering interaction between trend and seasonality, we have found that ambient PM2.5 has monotonously decreased all year long at all monitoring sites with similar patterns; this is characteristic of a regional-scale pollution. For ambient PM2.5-10 trend and season have a more complex, site-specific interaction, suggesting local sources and site location in the basin are relevant in determining ambient concentrations of coarse particles. A limitation of this study is that no quantitative link between ambient concentrations trends and atmospheric emissions could be established with the analyses carried out. A strength of the study is the long period analyzed with measurements conducted with the same gravimetric methodology.

Spatial distribution of ground-level urban background O3 concentrations in the Metropolitan Area of Buenos Aires, Argentina.

In this work, a recently developed urban-scale atmospheric dispersion model (DAUMOD-GRS) is applied to evaluate the ground-level ozone (O3) concentrations resulting from anthropogenic area sources of NOx and VOC in the Metropolitan Area of Buenos Aires (MABA). The statistical comparison of model results with observations (including new available data from seventeen sites) shows a good model performance. Estimated summer highest diurnal O3 1-h concentrations in the MABA vary between 15 ppb in the most urbanised area and 53 ppb in the suburbs. All values are below the air quality standard. Several runs are performed to evaluate the impact of possible future emission reductions on O3 concentrations. Under all hypothetical scenarios, the maximum diurnal O3 1-h concentration obtained for the area is slightly reduced (up to 4%). However, maximum diurnal O3 concentrations could increase at some less urbanised areas of MABA depending on the relative reductions of the emissions of NOx and VOC.