Highly Time-Resolved and Nontargeted Characterization of Volatile Organic Compound Emissions from Face Masks

Face covering by masks has become a lifeline for humans to prevent the airborne transmission of highly infectious SARS-CoV-2. One of the side effects, however, is the release of volatile organic compounds (VOCs), which can hardly be fully understood based on traditional offline measurements. Here, for the first time, we performed highly time-resolved and nontargeted measurements of VOCs emitted from face masks using an ultrasensitive proton transfer-reaction quadrupole-interface time-of-flight mass spectrometer. We found diverse VOC species, some of which are toxic. The chemical structures of the major VOC species were identified to be from the chemicals and processes involved in mask production. High concentrations of VOCs emitted from surgical masks (predominant mask type) were all concentrated in the initial 1 h and then dropped rapidly to an acceptable level after a process of naturally airing out. Higher emissions from a surgical mask for children are likely due to their colorful cartoon patterns. Despite the lowest emissions, the N95 respirator with an active carbon layer required 6 h to remove the toxic methanol. We support mask wearing to curtail the COVID-19 pandemic, but our results highlight the importance of naturally airing out masks to reduce zero-distance inhalation of mask-emitted VOCs.

Analysis of the Carbon Intensity of Container Shipping on Trunk Routes: Referring to the Decarbonization Trajectory of the Poseidon Principle

Container shipping industries are highly capital intensive. If shipping carriers want to execute international shipping financing, they must follow the IMO emission reduction targets and meet the decarbonization trajectory of the Poseidon Principle (PP). This article used an activity-based model to calculate container shipping industry carbon emissions. It was found that the carbon intensity per unit for each ship was decreased because of the upsizing of container vessels and route deployment based on the alliance strategy. On the Asia–Europe (A/E) trunk route, as the ship size increased from 11,300 to 24,000 TEU, the results showed that the carbon intensity ranged from 6.48 to 3.06 g/ton-nm. It is also proven that the mega-container deployment on the A/E trunk route followed the decarbonization trajectory proposed by PP, while the Asia–Pacific trunk route was not fully in line with the trajectory of EEOI/AER. It is worth noting that starting from 2020, due to the COVID-19 pandemic, shipping companies deployed a higher number of small-size vessels to boost revenues, resulting in more pollutants produced and a mismatch of the trajectory proposed by PP.

Elucidating the responses of highly time-resolved PM2.5 related elements to extreme emission reductions.

China's unprecedented lockdown to contain the spread of the novel coronavirus disease (COVID-19) in early 2020, provided a tragic natural experiment to investigate the responses of atmospheric pollution to emission reduction at regional scale. Primarily driven by primary emissions, particulate trace elements is vitally important due to their disproportionally adverse impacts on human health and ecosystem. Here 14 trace elements in PM2.5 were selected for continuous measurement hourly in urban representative site of Shanghai, for three different phases: pre-control period (1-23 January 2020), control period (24 January-10 February 2020; overlapped with Chinese Lunar New Year holiday) and post control period (11-26 February 2020) the city's lockdown measures. The results show that all meteorological parameters (including temperature, RH, mixing layer height et al.) were generally consistent among different periods. Throughout the study period, the concentrations of most species displayed a "V-shaped" trend, suggesting significant effects by the restriction measures imposed during the lockdown period. While this is not the case for species like K, Cu and Ba, indicating their unusual origins. As a case study, the geographical origins of Cu were explored. Seven major sources, i.e., Vehicle-related emission (including road dust; indicative of Ca, Fe, Ba, Mn, Zn, Cu; accounting for 30.1%), shipping (Ni; 5.0%), coal combustion (As, Pb; 4.2%), Se and Cr industry (24.9%), nonferrous metal smelting (Au, Hg; 7.5%) and fireworks burning (K, Cu, Ba; 28.3%) were successfully pinpointed based on positive matrix factorization (PMF) analysis. Our source apportionment results also highlight fireworks burning was one of the dominant source of trace elements during the Chinese Lunar New Year holiday. It is worth noting that 56% of the total mass vehicular emissions are affiliated with non-exhaust sources (tire wear, brake wear, and road surface abrasion).

[High-frequency Responses to the COVID-19 Shutdown of Heavy Metal Elements in PM2.5 in Shanghai].

To study the evolution and sources of heavy metal elements in the urban atmosphere before, during (overlapped with Chinese Lunar New Year), and after China's COVID-19 shutdown, a multi-metal online analyzer was deployed to determine the trace elements in PM2.5 in Shanghai from January 1 to February 26, 2020. Meanwhile, source apportionment of the hourly measured heavy metal concentrations was performed using a PMF model, in which eight sources were identified. The results show that the concentrations of most elements presented a "V-shaped" trend, which was mainly influenced by emissions from fireworks (K, Cu, Ba as indicative elements), Se-related industry, road dust (Ca, Fe, Ba), and motor vehicles (Mn, Zn, Fe, Cu). However, during the COVID-19 shutdown period, the concentrations of K, Ba, and Cu were high. Case-specific analysis suggested that prior to the shutdown period, the high concentrations of Cu were significantly influenced by long-range transport, which shifted to a dominant contribution from local fireworks during the shutdown period.

Measurement report of the change of PM2.5 composition during the COVID-19 lockdown in urban Xi'an: Enhanced secondary formation and oxidation.

Enhanced secondary aerosol formation was observed during the COVID-19 lockdown in Xi'an, especially for polluted episodes. More oxidized­oxygenated organic aerosol (MO-OOA) and sulfate showed the dominant enhancements, especially in large particle-mode. Meanwhile, relative humidity (RH) showed a positive promotion on the formation of sulfate and MO-OOA during the lockdown, but had no obvious correlation with less oxidized­oxygenated organic aerosol (LO-OOA) or nitrate. Organosulfurs (OS) displayed a higher contribution (~58%) than inorganic sulfate to total sulfate enhancement in the polluted episode during the lockdown. Although the total nitrate (TN) decreased during the lockdown ascribing to a larger reduction of inorganic nitrate, organic nitrate (ON) showed an obvious increase from pre-lockdown (0.5 ± 0.6 µg m-3 and 1 ± 2% of TN) to lockdown (5.3 ± 3.1 µg m-3 and 17 ± 9% of TN) in the polluted case (P < 0.05). In addition, RH also displayed a positive promotion on the formation of ON and OS, and the increases of both OS and ON were much efficient in the nighttime than in the daytime. These results suggest that higher RH and stagnant meteorology might facilitate the sulfate and MO-OOA enhancement, especially in the nighttime, which dominated the secondary aerosol enhancement in haze pollution during the lockdown.

Enhanced formation of secondary organic aerosol from photochemical oxidation during the COVID-19 lockdown in a background site in Northwest China.

The COVID-19 pandemic has drastically affected the economic and social activities, leading to large reductions in anthropogenic emissions on a global scale. Despite the reduction of primary emissions during the lockdown period, heavy haze pollution was observed unexpectedly in megacities in North and East China. In this study, we conducted online measurements of organic aerosol in a background site before and during the lockdown in Guanzhong basin, Northwest China. The oxygenated organic aerosol (OOA) increased from 24% of total OA (3.2 ± 1.6 µg m-3) before lockdown to 54% of total OA (4.5 ± 1.3 µg m-3) during lockdown, likely due to substantial decrease of NOx emissions during lockdown which resulted in large increase of O3 and thus atmospheric oxidizing capacity. OOA showed higher mass concentrations and fractional contributions during lockdown than before lockdown, and increased with the increase of Ox in both periods. In comparison, aqueous secondary organic aerosol (aqSOA) showed high mass concentrations and fractional contributions in both polluted periods before and during lockdown with the increase of aerosol liquid water content (ALWC). The increase of aqSOA under high ALWC conditions is very likely the reason of pollution events during lockdown. Combined with trajectory analysis, the absence of Guanzhong cluster in polluted period during lockdown may play a key role in the OA variations between two polluted periods. In addition, when comparing the clusters from the same transmission directions between before lockdown and during lockdown, the OA fractions showed similar variations during lockdown in all clusters, suggesting the OA variations are widespread in northwest China.

Puzzling Haze Events in China During the Coronavirus (COVID-19) Shutdown.

It is a puzzle as to why more severe haze formed during the New Year Holiday in 2020 (NYH-20), when China was in an unprecedented state of shutdown to contain the coronavirus (COVID-19) outbreak, than in 2019 (NYH-19). We performed a comprehensive measurement and modeling analysis of the aerosol chemistry and physics at multiple sites in China (mainly in Shanghai) before, during, and after NYH-19 and NYH-20. Much higher secondary aerosol fraction in PM2.5 were observed during NYH-20 (73%) than during NYH-19 (59%). During NYH-20, PM2.5 levels correlated significantly with the oxidation ratio of nitrogen (r 2 = 0.77, p < 0.01), and aged particles from northern China were found to impede atmospheric new particle formation and growth in Shanghai. A markedly enhanced efficiency of nitrate aerosol formation was observed along the transport pathways during NYH-20, despite the overall low atmospheric NO2 levels.