Environmental science: atmospheres最新文献

PAN (CH₃C(O)O₂NO₂) is often the most important chemical reservoir of reactive nitrogen compounds throughout the free- and upper troposphere and provides a means of transport of reactive nitrogen from source regions to more remote locations. Both PAN and PAA (peroxy acetic acid, CH₃C(O)OOH) are formed exclusively via reactions of the CH₃C(O)O₂ radical, with PAA favoured under low NO_X conditions. We present airborne measurements of PAN and PAA taken with a chemical-ionisation mass spectrometer on board the High Altitude-Long range (HALO) aircraft over the North and tropical Atlantic Ocean west of Africa in August–September 2018. Our observations showed that mixing ratios of PAN and PAA are enhanced in biomass-burning impacted air masses and we determined molar enhancement ratios for both trace gases relative to CO and CH₃CN. The PAA-to-PAN ratio was enhanced in biomass-burning impacted air masses compared to background air, which may reflect the continued photochemical formation of PAA in such plumes even after NO_X has been largely depleted. This was confirmed by the large ratio of PAN/(PAN + NO_X), which was on average ≈0.8 at 7–8 km altitude and approached unity in biomass burning impacted air masses. Although no measurements of total reactive nitrogen species (NO_y) or HNO₃ were available, a major fraction of NO_X was likely sequestered in the form of PAN in this region, especially in air masses that had been impacted by biomass burning.

This paper provides a chronological review of the governance history of solar radiation management (SRM), also called solar geoengineering, from 2006 to 2024. Often characterized as an ungoverned space, we argue that the governance landscape for SRM is actually quite rich, though activity is primarily in the Global North, where research and governance capacity is concentrated. We illuminate the many governance initiatives and mechanisms in this area, explaining each mechanism's significance, relevant politics, and intersections with questions of environmental justice. We then identify gaps, limitations, possible future developments, and key contestations, including as related to justice. Crucially, as the chronological review shows, historical developments have largely occurred within a handful of countries in the Global North, laying bare the need to strengthen ongoing efforts to capacitate climate vulnerable countries in the Global South so they can more effectively shape the trajectory of SRM governance. We conclude by offering suggestions for future governance development.

The kinetics of the reactions of mercurous bromide (HgBr) with NO₂ and O₂ have been studied using the pulsed laser photolysis – pulsed laser induced fluorescence technique in nitrogen, air and helium at room temperature and as a function of pressure. For reaction with NO₂, temporal profiles showed good pseudo-first order behavior and we see a three-body recombination and obtain rate coefficients of ∼1–7 × 10⁻¹¹ cm³ per molecules per s over the pressure range 50–700 Torr in nitrogen. As expected, He is a less efficient 3rd body and rates are somewhat slower. We monitored the presence of a reduction channel regenerating Hg(0) and saw no evidence for it occurring. We obtained temporal profiles of HgBr at pressures of up to 500 Torr of O₂ demonstrating that laser induced fluorescence has adequate sensitivity as a concentration diagnostic in laboratory studies. The temporal profiles showed no evidence for any reaction between HgBr and O₂ at room temperature.

Terpenoids, including isoprene and monoterpenes, are highly reactive volatile organic compounds (VOCs) that play an essential role in atmospheric chemistry, contributing to the formation of ozone and secondary organic aerosols (SOAs). While known for decades for their biogenic origin, their anthropogenic origin is now well established in urban areas worldwide. Nevertheless, there is still a lack of clarity regarding the relative significance of these emissions and their impact on secondary pollution at the urban scale where biogenic and anthropogenic emissions coexist. The objective of this study is to evaluate the role of anthropogenic terpenoids in secondary pollution over the megacity of Paris, a typical northern mid-latitude urban area, using a box model. The model employs the Master Chemical Mechanism (MCM v3.3.1) to describe the gaseous reactivity. A physico-chemical scenario was developed to reproduce a typical summertime environment built upon in situ observations collected during the EU-MEGAPOLI campaign in Paris. Emission ratios of anthropogenic VOCs over carbon monoxide were used to parametrize the primary emissions of more than 60 species (including anthropogenic terpenoids). The comparison between in situ observations and modelled trace gas concentrations demonstrated the model's capacity to reproduce the levels and their temporal variability. Two sensitivity tests were conducted to quantify the impact of terpenoid emissions on ozone formation and their potential to form SOA mass concentration according to two simulations modulating anthropogenic and biogenic emissions of terpenoids based on the uncertainties associated with their estimation. Ozone concentration slightly increases by 1 (±0.5)% when increasing anthropogenic terpenoid emissions and by 3 (±2)% when increasing biogenic terpenoid emissions; the increase of O₃ with increasing VOCs is consistent with the high-NO_x chemical regime. Looking at the potential terpenoid derived SOA production, isoprene and limonene dominate. The estimated total mass concentration of SOAs produced over a 24 h period is 0.53 μg m⁻³, with a maximum hourly produced mass concentration of 0.045 μg m⁻³ observed in the morning. This modelling study suggests that the production of SOAs through the oxidation of terpenoids emitted from anthropogenic sources is competitive with that derived from their biogenic sources and remains significant at night.

The emissions of nitrogen oxides (NO_x) from combustion have been regulated for several decades with substantial reductions in national totals being reported in high-income countries since the 1990s. Most technical regulation on emissions is sectoral, appliance specific, and uses metrics aligned to activity data, for example grams of NO_x per kilometre driven or grams per kilonewton thrust. It is not straightforward therefore to compare the relative stringency of emission regulation between sectors. Here we undertake a regulatory assessment placing all the key NO_x emitting sectors onto a common grams of NO_x per kilowatt hour (g_[NOx] kWh⁻¹) baseline, covering appliances as small as 1 kW to greater than 2 GW. This common scale facilitates meaningful regulatory comparisons and may help to inform future policy decisions. We find little regulatory consistency between sectors when viewed on a per kWh output basis, with non-road mobile machinery (NRMM), medium combustion plant (MCP), maritime and civil aviation having more permissive regulatory limits when compared to emissions from passenger cars and domestic boilers. This difference can be large for appliances with the same nominal power rating; for example, the allowable NO_x emissions for a backhoe loader are 4.3 times higher than those for a passenger car. Transparency in pollutant emissions varies considerably between sectors. Data from MCPs and the Industrial Emissions Directive (IED) are less accessible due to commercial sensitivities and the use of less definitively defined principles of ‘Best Available Techniques’. Whilst electrification is likely in the long-term to eliminate some NO_x sources, it is notable that this will be in sectors that currently have more stringent regulatory limits (e.g. road transport, domestic heating). More permissively regulated sectors such as NRMM, MCPs and aviation are likely to retain combustion systems and will continue to emit substantial NO_x unless the adoption of low carbon fuel is accompanied by revision of NO_x emission standards.

Highly oxygenated organic molecules (HOMs) are significant contributors to the formation of secondary organic aerosols (SOAs) and new particles in the atmosphere. The process of HOM formation via autoxidation is highly dependent on several factors, such as temperature, relative humidity (RH), and initial ozone concentration, among others. The current work investigates how temperature and RH affect the formation of HOMs in SOAs from limonene ozonolysis. Experiments were conducted in a laminar flow tube reactor under different experimental conditions (T = 5 °C and 25 °C; RH = 15% and 75%). A scanning mobility particle sizer was used to measure the concentration and size distribution of generated SOA particles. Fourier transform ion cyclotron resonance mass spectrometry was used to detect and characterize HOMs and SOAs. Experimental results show that lower temperatures (i.e., T = 5 °C) and higher RH levels (e.g., RH = 75%) promote the generation of HOMs and SOAs. Limonene-oxidation-derived HOMs exhibit a preference for stabilization under low-temperature and high-RH conditions. Within this context, semi-volatile, low-volatile, and extremely low-volatile organic compounds play a significant role. Our experimental findings indicate that the formation of C₁₀ compounds during limonene ozonolysis is strongly influenced by peroxy radical chemistry. Given that peroxy radicals are key intermediates in this process, their reactions—including autoxidation and bimolecular termination pathways—likely play a significant role in the formation and stabilization of HOMs in SOAs. The observed product distributions also suggest that these radicals contribute to the incorporation of multiple oxygen atoms, facilitating the formation of ELVOCs and LVOCs that ultimately drive particle-phase growth. The present work can improve our understanding of the generation of biogenic HOMs and SOAs at different temperatures and RH, which can be used in future exposure risk or climate models to provide more accurate air quality prediction and management.

Recently Pérez-Peña et al. published a paper in this journal on the potential atmospheric fate of trifluoroacetaldehyde (CF₃CHO) as a source of CF₃H (HFC-23). In their work they utilized both a box model and a global chemistry and transport model to evaluate the production of CF₃H from the photolysis of CF₃CHO, the latter generated from photochemical oxidation of HFO-1234ze (CF₃CHCHF). Certain chemical assumptions and simplifications were made. We believe the assumptions utilized by Pérez-Peña et al. misrepresent the environmental fate of CF₃CHO. In the following, we present our comments on both the photolysis and the wet and dry deposition of CF₃CHO. Furthermore, we contemplate the impact of the potential deposition of CF₃CHO on the formation of trifluoroacetic acid (CF₃COOH) during the environmental processing of CF₃CHO.

In Pérez-Peña et al. (DOI: https://doi.org/10.1039/d3ea00120b), we used a suite of box model simulations to determine how trifluoroacetaldehyde (CF₃CHO) produced from HFO-1234ze is lost in the atmosphere and how much fluoroform (CHF₃ or HFC-23) could potentially be produced as a result. For the first time in any modelling study, our simulations included both a minor CF₃CHO photolytic loss channel leading to CHF₃ production and physical removal of CF₃CHO via wet and dry deposition. In their comment, Sulbaek Andersen, Nielsen, and Franklin query the assumptions used to simulate these processes. Here, we show that the importance of the photolytic loss pathway remains a matter of community debate and that our results are relatively insensitive to assumptions underlying simulation of deposition. We reiterate the need for measurements of CF₃CHO physical properties to reduce the uncertainties in these processes and pave the way for more sophisticated models.

Wildfires are a major source of aerosols during summer in the western United States. Aerosols emitted from wildfires could significantly affect air quality, human health, and the global climate. This study conducted a comparison of aerosol characteristics during wildfire smoke-influenced and non-smoke-influenced days. Ambient particle size distribution (PSD) data were collected in Reno, Nevada, between July 2017 and October 2020. During this period, the site was impacted by smoke from over a hundred wildfires burning in a wide range of ecosystems in the western United States located at different distances from the measurement site. The smoke-influenced days were identified using satellite images, a hazard mapping system, and wind back-trajectory. Positive matrix factorization (PMF) was applied to identify the main sources and their characteristics. The wildfire aerosols were observed to have a number mode diameter of 212 nm, which is significantly larger than aerosols on non-smoke-influenced days (61 nm). In addition to the increase in particle size, wildfires made a large contribution to PM_2.5 and CO concentrations. During fire-prone months (July, August, and September) from 2016 to 2021, 56% to 65% of PM_2.5 and 18% to 26% of CO concentrations could be attributed to wildfire emissions in the study area. On an annual basis, wildfire emissions were responsible for 35% to 47% of PM_2.5 concentrations and 5% to 12% of CO concentrations.

Several studies have analyzed and reported the relationship between particulate matter (PM) in the air and its adverse health effects, primarily on fetal development and subsequent early childhood. This study aims to understand how outdoor air made up of mainly PM, influences indoor air quality in a naturally ventilated maternity ward in an urban hospital setting. The data collection site in this study was the Dr Jose Fabella Memorial Hospital, a maternity hospital located in Manila, Philippines. Indoor and outdoor PM_2.5 levels from November 2021 to June 2022 were investigated. A strong positive correlation (r² ranging from 0.78 to 0.98) was observed between the daily outdoor and indoor PM levels. While the median concentrations were above the World Health Organization (WHO) air quality guidelines, they were below the Philippine National Ambient Air Quality Guideline Values (NAAQGV) at the time of data collection. These results underscore the importance of updating guideline values. Indoor-to-outdoor diurnal ratios (I/O), ranging from 0.77 to 1.33, with peak times (indoor-source-dominated) between 12:00 and 13:00 and trough times (outdoor-source-dominated) between 04:00 and 05:00, offered insight into the times of the day dominated by indoor versus outdoor sources and highlighted the need for continuous air monitoring while providing additional protection in indoor spaces, such as clear indoor air quality guidelines combined with indoor ventilation and filtration requirements. These results highlight the need for a holistic air quality management approach which focuses concurrently on both ambient and indoor air quality in healthcare facilities. Naturally ventilated hospitals must be included as a priority monitoring site, as they are a critical in improving air quality in the context of public health protection.