Volatile organic compounds measured by proton transfer reaction mass spectrometry over the complex terrain of Quintero Bay, Central Chile.

This research provides new evidence regarding the different kinds of air quality episodes, and their underlying mechanisms, that frequently impact the urban area of Quintero Bay in Central Chile, which is located along complex coastal terrain and is surrounded by industries. The monitoring campaign was carried out in January 2022 and encompassed two distinctive meteorological regimes. The first part of the month was dominated by a coastal low centered to the south of Quintero, which resulted in prevailing northerly flow (or weak southerlies) and a deep cloud-topped marine boundary layer. After a 2-3-day transition, the latter collapsed, and a clear-sky regime ensued, which was characterized by a shallow boundary layer and strong southerly winds during the daytime that lasted until the end of the campaign. By using proton transfer reaction time of flight mass spectrometry (PTR-TOF-MS) at a high temporal resolution (1 s), we measured high levels of volatile organic compounds (VOCs) during air quality episodes in real time. The episodes detected were associated with different prevailing meteorological regimes, suggesting that different point sources were involved. In the first episode, propene/cyclopropane, butenes, benzene, toluene and ethylbenzene/xylenes were associated with north and northwesterly weak winds. Complaints associated with hydrocarbon odor were reported. The pollution originated from industrial and petrochemical units located to the north of Quintero, which transport and store natural gas, liquified petroleum gas and oil. The second episode was linked to an oil refinery located south of our measurement site. In this case, high levels of phenol, furan and cresols occurred under strong southwesterly winds. During this event, headaches and dizziness were reported. By contrast, the levels of other aromatic compounds (benzene, toluene, ethylbenzene/xylenes) were lower than in the first air pollution episode.

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.

The effects of the built environment, traffic patterns, and micrometeorology on street level ultrafine particle concentrations at a block scale: Results from multiple urban sites.

This study attempts to explain explicitly the direct and quantitative effects of complicated urban built-environment on near-road dispersion and levels of vehicular emissions at the scale of several city blocks, based on ultrafine particle concentrations ([UFP]). On short timescales, ultrafine particles are an excellent proxy for other roadway emissions. Five measurement sites in the greater Los Angeles with different built environments but similar mesoscale meteorology were explored. After controlling for traffic, for most sampling days and sites, morning [UFP] were higher than those in the afternoon due to limited dispersion capacity combined with a relatively stable surface layer. [UFP] at the intersection corners were also higher than those over the sampling sites, implying that accelerating vehicles around the intersections contributed to [UFP] elevation. In the calm morning, the areal aspect ratio (Ararea), developed in this study for real urban configurations, showed a strong relationship with block-scale [UFP]. Ararea includes the building area-weighted building height, the amount of open space, and the building footprint. In the afternoon, however, when wind speeds were generally higher and turbulence was stronger, vertical turbulence intensity σw was the most effective factor controlling [UFP]. The surrounding built environment appears to play an indirect role in observed [UFP], by affecting surface level micrometeorology. The effects are substantial; controlling for traffic, differences in Ararea and building heterogeneity were related to differences in [UFP] of factors of two to three among our five study sites. These results have significant implications for pedestrian exposure as well as transit-oriented urban planning.

Screening and determination of pesticides in soil using continuous subcritical water extraction and gas chromatography-mass spectrometry.

In the present work the efficiency of water under subcritical conditions for the extraction of pesticides having a broad spectrum of polarities from soils was evaluated. The pesticides under study were carbofuran, hexachlorobenzene, dimethoate, simazine, atrazine, lindane, diazinon, methylparathion, alachlor, aldrin-R, metholachlor, chlorpyrifos, heptachlor epoxide, dieldrin, endrin, 4,4-DDT and metoxichlor. Optimization studies were carried out using a blank soil (Non-Polluted Soil 1, CLN-1, RTC) and a real soil which were previously spiked with the pesticide mixture and aged for 60 days. A laboratory-made aluminum oven with controlled temperature was used to carry out the leaching process with subcritical water, where it is placed a pre-heater and the extraction cell. The following variables were studied, keeping the pressure controlled about 1200 p.s.i.: the extraction temperature, the time of static and dynamic extraction and the flow-rate of water (1 p.s.i. = 6894.76 Pa). The extraction efficiency of the pesticides increases with the temperature trending to the quantitative extraction at temperatures near to 300 degrees C. After the extraction process, the analytes were transferred quantitatively to 5 ml dichloromethane, before the determination by GC-MS. The results indicate that under the optimized conditions mostly of the analytes are extracted quantitatively in 90 min with recoveries quite similar to those obtained by the standard Soxhlet extraction procedure. Alternatively, by using an extraction time of 25 min, the method can be used as screening for all the pesticides, with recoveries depending on their polarity.

A five-year study of particulate matter (PM2.5) and cerebrovascular diseases.

Cerebrovascular accidents, or strokes, are the second leading cause of mortality and the leading cause of morbidity in both Chile and the rest of the world. However, the relationship between particulate matter pollution and strokes is not well characterized. The association between fine particle concentration and stroke admissions was studied. Data on hospital admissions due to cerebrovascular accidents were collected from the Ministry of Health. Air quality and meteorological data were taken from the Air Quality database of the Santiago Metropolitan Area. Santiago reported 33,624 stroke admissions between January 1, 2002 and December 30, 2006. PM2.5 concentration was markedly seasonal, increasing during the winter. This study found an association between PM2.5 exposure and hospital admissions for stroke; for every PM2.5 concentration increase of 10 µg m(-3), the risk of emergency hospital admissions for cerebrovascular causes increased by 1.29% (95% CI 0.552%-2.03%).

Ozone weekend effect in Santiago, Chile.

The study examined weekday-weekend differences in ozone, NO(x) (NO and NO(2)) and VOC concentrations in Santiago, Chile, from 1999 to 2007. The results provide evidence for the occurrence of an atmospheric phenomenon that produces higher ozone concentrations during weekends despite lower concentrations of ozone precursors. This phenomenon is known as the weekend effect (WE). The overall ozone decrease since the spring of 2004 was a consequence of the implementation of several urban pollution control measures. Although these measures caused a decline in the number of days that exceed the national standard from two-thirds to one-third of summer days, the WE, which became statistically significant beginning in September 2004, could not be eliminated. Furthermore, VOC/NO(x) ratios decreased during the same period (2004), especially in the most industrialized area of Santiago. Similarly, under these regimes, the VOC/NO(x) ratios were higher on Sundays than on weekdays and caused higher ozone concentrations on Sundays.

Uncertainty of ozone measurements with the primary standard reference photometer (SRP45).

A comparison of the ozone primary reference standard photometer serial number 45 (SRP45) against the National Institute of Standards and Technology (NIST) instruments, serial number 0 (SRP0) and 2 (SRP2), has been performed in order to establish the traceability and comparability of ozone measurements made by the Chilean atmospheric science community. A complete uncertainty budget was developed for SRP45, using a GUM approach. The results of the comparisons allow us to conclude that SRP45, SRP0 and SRP2 are comparable according to international criteria over an ozone mole fraction range of 0 nmol mol(-1) to at least 500 nmol mol(-1). The official result for the validation of SRP45 is x(ozone)(SRP45)=[0.013+0.99806x(ozone)(SRP2)] nmol mol(-1) with an expanded uncertainty of [Formula in text] from 0 to 500 nmol mol(-1).