Editorial: Anthropogenic trace gases and their linkages to meteorology and climate change

Editorial on the Research Topic
Anthropogenic trace gases and their linkages to meteorology and climate change

Anthropogenic trace gases and climate change are the most significant environmental problems that mankind has been confronting in recent years. About 55% of the world's population lives in urban areas, and this trend is expected to continue to 68% by 2050 (Molina, 2021). Urbanization and economic growth in developing countries are accelerating, can lead to higher levels of trace gases [e.g., surface ozone (O₃), volatile organic compounds (VOCs), oxides of nitrogen (NOx), sulfur dioxide (SO₂), carbon monoxide (CO, etc.) and particulate matter (PM_2.5 and PM₁₀)], resulting in sharp decline air quality (Fu and Chen, 2017) and poses threats to human health and ecosystems health (Apte et al., 2018). Additionally, the cocktail of high concentrations of pollutants has caused frequent pollution episodes and low visibility (Molnar et al., 2020). DeLang et al. (2021) have reported that O₃ exposure in Asia and Africa has been increasing globally, partly due to highly populated and polluted regions. Moreover, it has been worsening mainly in low- and middle-income countries, driven by anthropogenic activities (Silva et al., 2016; Turnock et al., 2020). Surface O₃ naturally occurs in low amounts, but unhealthy O₃ is formed when high levels of anthropogenic trace gases, such as VOCs and CO, oxidize in the presence of solar flux and a sufficient amount of NOx in the lower troposphere (Yadav et al., 2022) (Equation 1).

$\begin{array}{l}\text{VOC}+\text{NOx}+\text{sunlight}\to {\text{O}}_3+“\text{carbonylsproducts}”\\ +“\text{secondaryorganicaerosol}(\text{SOA})”& (1)\end{array}$

Surface O₃ is a criteria pollutant and greenhouse gas that is bad for humans, vegetation, and nature. O₃ exposure mortality worldwide was estimated at ~365,000 [95% uncertainty interval (UI): 175,000, 564,000] in the year 2019 (Malashock et al., 2022). SOA is a significant component of particulate matter (Guenther et al., 2006), particularly particles with a diameter of 2.5 microns or less (PM_2.5). Particulate matter has a very complex composition, and its main components are trace elements, carbon-containing components, sulfates (SO4²⁻), nitrates (${\text{NO}}_3^{-}$), ammonium salts (${\text{NH}}_4^{+}$), organic matter, etc. (Jun et al., 2013).

Some VOC products may also participate in forming and growing new particles, known as SOA. On the other hand, the conversion of gaseous precursors (SO₂, NOx, and NH₃) is the key pathway to form ${\text{SO}}_4^{2-}$, ${\text{NO}}_3^{-}$, and ${\text{NH}}_4^{+}$, such as gas-phase, aqueous phase, and heterogeneous reactions. Among them, ${\text{SO}}_4^{-2}$ is ubiquitous and is a key constituent of PM_2.5 in the atmosphere, accounting for 10–35% of total mass. PM_2.5 is a major cause of haze and can scatter and absorb sunlight, reduce atmospheric visibility, and increase radiation forcing, leading to global climate change (Cheng et al., 2016; Liu et al., 2020). The changes in the mixing ratios of anthropogenic trace gases and the role of this in different aspects have become significant concerns. Hence, the proposed Research Topic was motivated to investigate the information on their origins and sinks, physical and chemical processes, and distribution of trace gases, which are vital for accurately predicting the environment and climate conditions. A total of six research and one review article have been published on the current topic under the particular issue, which is related to air quality and its link to climate change and meteorology.

What we know about the history of the novel coronavirus, which we call COVID-19, is that it was first detected at the end of 2019 in Wuhan, China, and set off a global pandemic. Therefore, many countries have taken action and imposed lockdowns to preventive measures around the world to combat COVID-19, but at the same time, environmental conditions like air quality for the moment have led to significant improvements due to reductions in anthropogenic activities. However, besides local anthropogenic emissions, the air pollution footprints are unique over the Arabian Peninsula (AP), where natural mineral dust is dominated. Hence, Karumuri et al. have reported the role of the COVID−19 lockdown in the distribution of aerosol (PM_2.5, PM₁₀, and AOD) and trace gases (NO₂ and SO₂) concentrations over the Arabian Peninsula (AP). They used in-situ and satellite datasets, and WRF-Chem simulations were performed to investigate the changes in emissions during the lockdown period. They suggested that the COVID-19 lockdown over AP significantly reduces the trace gas levels, but no improvement was seen in particulate pollution. and has a slight impact on the particulate concentrations over the central and northern AP due to the dominant contribution of dust emissions to the particulate concentrations. It indicates that dust emissions and large-scale dynamics play an important role in particulate pollution levels over the AP. The study's implication could be very important for air quality where dust emissions are a prominent source.

The solar eclipse provides a rare opportunity to take measurements of trace gases and weather parameters to observe the photochemistry under atmospheric conditions when solar radiation reduces. The annual solar eclipse occurred on 21 June 2020, and hence, Prakash et al. have highlighted how solar eclipses impact the atmospheric trace gases and weather parameters over Northwestern India with the help of statistical analyses. By comparing the normal days, they found large variations in trace gases with meteorological parameters and about a 23% reduction in O₃ during the solar eclipse day. Overall, this study can suggest the essential implications of the dynamics of photochemical processes.

Volatile organic compounds (VOCs) are the most reactive species and play a significant role in the photochemical processes despite their presence at very low in the air, which is now getting more and more attention. Therefore, air quality monitoring networks have also added VOC measurements in recent years in addition to the criteria pollutants like CO, NOx, O₃, and PMs (Lee et al., 2002). Long-term exposure to elevated aromatic VOC concentrations can cause acute and chronic health issues. Sahu et al. reported BTEX variations and weather parameters on different time scales over an eastern Indian site, Bhubaneswar, based on 2 years of continuous measurements. They also highlight the CO and NOx emissions patterns for the study region. They suggested that traffic is the most dominant source of NO_X, VOC, and CO at Bhubaneswar rather than residential and industrial sectors. Lower BTEX concentrations were in pre-monsoon and monsoon seasons due to the wash-out effect in locally generated and transported air. The transport of oceanic air resulted in the lowest pollution concentrations during these seasons. Overall, these results imply that controlling traffic-related emissions would be the main advantage to improving air quality.

O₃ is controlled by its production, sink, and net transport (advection/convection and diffusive) in the atmosphere. Sagar et al. represent how chemical kinetics control O₃ variability on diurnal and seasonal time scales using known chemical kinetics and a radiative transfer model at the study site in South India. In this work, they conducted continuous long-term measurements of O₃, nitrogen oxides (NOx = NO + NO2), and meteorological data in the suburban location of Shadnagar, India. Data analyses were performed to investigate the governing processes that control O₃ variability on diurnal and seasonal time scales. The role of chemistry in O₃ variability, including formation and destruction processes, was investigated using known chemical kinetics and a radiative transfer model. The average net production and net transport of near-surface O₃ were 3.18 and 0.87 ppbv/h, respectively, while horizontal advection was 0.01 ppbv/h in the daytime. The production of O₃ was found to be dominant, indicating the influx of ozone at the site. Overall, they suggested spatio-temporal variability in near-surface O₃ is strongly controlled by net production in Shadnagar and may be applicable in similar environments globally. These results help to understand the O₃ chemistry and its sources affecting air quality.

Typically, most of the time in a year, air quality is determined by particulate pollutants, and the high loading of aerosols in most cities in India poses a significant challenge for policymakers to bring down the pollution level within the ambient air quality standard (Balakrishnan et al., 2019). Payra et al. have performed a comprehensive evaluation of aerosol optical depth (AOD) products which has retrieved from two satellites, including Visible Infrared Imaging Radiometer Suite (VIIRS) and Aqua-Moderate-Resolution Imaging Spectroradiometer (MODIS) over India. The study has also highlighted the validation of satellite AOD and ground-based AOD from AERONET at 550 nm wavelength. Overall, the study shows that both satellites offer high-quality AOD products, while MODIS performs slightly better than VIIRS over India. Overall, High-resolution satellites are essential in monitoring and evaluating accurate and precise air quality information.

Choudhary et al. reported the features of air pollutants (PM_2.5, PM₁₀, NO₂, CO, O₃, and SO₂) and their prediction using data mining algorithms from 01 January 2019 to 01 June 2021 in India's industrial eastern coastal state. Overall, The study outcome will be helpful to environmental policymakers in understanding the distribution of air pollutants and how to strategize air pollution reductions and enhance air quality.

Dewan and Lakhani have presented an up-to-date review article discussing ozone and its precursor gases, emission sources, dynamics, chemistry, and linkages with climate change connection. It has also highlighted the challenges and limitations associated with climate-O₃ linkages and their incorporation in models due to uncertainties in the magnitude and signs of projected precursor emissions in response to future climate change and the difference in models.

Author contributions

RY: Writing—original draft, Writing—review & editing. VA: Writing—original draft, Writing—review & editing. SS: Writing—original draft, Writing—review & editing. RK: Writing—original draft, Writing—review & editing. BT: Writing—original draft, Writing—review & editing. GB: Writing—original draft, Writing—review & editing.

Funding

The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision.

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