Role of the Terrestrial Biosphere in Atmospheric Chemistry and Climate

Seasonal biogenic volatile organic compound emission factors in temperate tree species: Implications for emission estimation and ozone formation

Variability in biogenic volatile organic compound (BVOC) emissions across species and seasons poses challenges for accurate regional emission estimates and effective ozone (O3) control policies. To address this issue, we conducted in-situ measurements of emission factors for six dominant tree species in Beijing across four seasons. Subsequently, we developed monthly dynamic standard emission factors (SER-MDs) to model monthly BVOC emissions and their impacts on O3 formation at citywide and district levels. Our observations revealed pronounced seasonal differences in the BVOC composition and emission rates, as well as their responsiveness to monthly average temperature. By introducing the SER-MDs, we estimated BVOC emissions from the dominant tree species in Beijing to be 38.2 Gg yr-1, with monoterpenes and isoprene contributing 49% and 11%, respectively. This calculation reduced the overestimation associated with constant standard emission factors by 31%-38% at district level. The estimates also revealed regional differences in plant compositions rather than simple feedback from regional temperature and photosynthetically active radiation periods. Under these conditions, the maximum monthly BVOC-induced O3 concentration occurred in August and ranged from 4 to 17 μg m-3 across districts, with isoprene being the dominant contributor. Quercus mongolica and Populus tomentosa played significant roles in the formation of BVOC-induced O3 due to their strong isoprene emitting potential in July-August. These results indicate the necessity of introducing species-specific rhythms of BVOC emissions from dominant species in the development of urban BVOC emission inventories. This approach could inform the development of air pollution management policies that are consistent with the local vegetation composition and O3 pollution characteristics. For Beijing and other similar northern cities, reducing the use of tree species emitting substantial amounts of isoprene during periods of regional peak ambient O3 concentrations could constitute an effective nature-based solution for improving urban air quality in the future.

Detection of morphological and eco-physiological traits of ornamental woody species to assess their potential Net O3 uptake

Urban greening can improve cities' air quality by filtering the main gaseous pollutants such as tropospheric ozone (O3). However, the pollutant removal capacity offered by woody species strongly depends on eco-physiological and morphological traits. Woody species with higher stomatal conductance (gs) can remove more gases from the atmosphere, but other species can worsen air quality due to high O3 forming potential (OFP), based on their emitting rates of biogenic volatile organic compounds (bVOCs) and Leaf Mass per Area (LMA). Presently, there is a lack of data on eco-physiological (gs, bVOCs emissions) and foliar traits (LMA) for several ornamental species used in urban greening programs, which does not allow assessment of their O3 removal capacity and OFP. This study aimed to (i) parameterize gs, assess bVOCs emissions and LMA of 14 ornamental woody species commonly used in Mediterranean urban greening, and (ii) model their Net O3 uptake. The gs Jarvis model was parameterized considering various environmental conditions alongside isoprene and monoterpene foliar bVOCs emission rates trapped in the field and quantified by gas chromatography-mass spectrometry. The results are helpful for urban planning and landscaping; suggesting that Catalpa bignonioides and Gleditsia triacanthos have excellent O3 removal capacity due to their high maximum gs (gmax) equal to 0.657 and 0.597 mol H2O m-2 s-1. Regarding bVOCs, high isoprene (16.75 μg gdw-1 h-1) and monoterpene (13.12 μg gdw-1 h-1) emission rates were found for Rhamnus alaternus and Cornus mas. In contrast, no bVOCs emissions were detected for Camellia sasanqua and Paulownia tomentosa. In conclusion, 11 species showed a positive Net O3 uptake, while the use of large numbers of R. alaternus, C. mas, and Chamaerops humilis for urban afforestation planning are not recommended due to their potential to induce a deterioration of outdoor air quality.

Contribution of Particulates to Airborne Disease Transmission and Severity: A Review

The emergence of coronavirus disease 2019 (COVID-19) has catalyzed great interest in the spread of airborne pathogens. Airborne infectious diseases are classified into viral, bacterial, and fungal infections. Environmental factors can elevate their transmission and lethality. Air pollution has been reported as the leading environmental cause of disease and premature death worldwide. Notably, ambient particulates of various components and sizes are harmful pollutants. There are two prominent health effects of particles in the atmosphere: (1) particulate matter (PM) penetrates the respiratory tract and adversely affects health, such as heart and respiratory diseases; and (2) bioaerosols of particles act as a medium for the spread of pathogens in the air. Particulates contribute to the occurrence of infectious diseases by increasing vulnerability to infection through inhalation and spreading disease through interactions with airborne pathogens. Here, we focus on the synergistic effects of airborne particulates on infectious disease. We outline the concepts and characteristics of bioaerosols, from their generation to transformation and circulation on Earth. Considering that microorganisms coexist with other particulates as bioaerosols, we investigate studies examining respiratory infections associated with airborne PM. Furthermore, we discuss four factors (meteorological, biological, physical, and chemical) that may impact the influence of PM on the survival of contagious pathogens in the atmosphere. Our review highlights the significant role of particulates in supporting the transmission of infectious aerosols and emphasizes the need for further research in this area.

Release of biogenic volatile organic compounds and physiological responses of two sub-tropical tree species to smoke derived from forest fire

Forests emit a large amount of biogenic volatile organic compounds (BVOCs) in response to biotic and abiotic stress. Despite frequent occurrence of large forest fires in recent years, the impact of smoke stress derived from these forest fires on the emission of BVOCs is largely unexplored. Thus, the aims of the study were to quantify the amount and composition of BVOCs released by two sub-tropical tree species, Cunninghamia lanceolata and Schima superba, in response to exposure to smoke. Physiological responses and their relationship with BVOCs were also investigated. The results showed that smoke treatments significantly (p < 0.001) promoted short-term release of BVOCs by C. lanceolata leaves than S. superba; and alkanes, olefins and benzene homologs were identified as major classes of BVOCs. Both C. lanceolata and S. superba seedlings showed significant (p < 0.005) physiological responses after being smoke-stressed where photosynthetic rate remained unaffected, chlorophyll content greatly reduced and Activities of anti-oxidant enzymes and the malondialdehyde content generally increased with the increase in smoke concentration. Activities of anti-oxidant enzymes showed mainly positive correlations with the major BVOCs. In conclusion, the release of BVOCs following smoke stress is species-specific and there exists a link between activities of antioxidant enzymes and BVOCs released. The findings provide insight about management of forest fires in order to control excessive emission of smoke that would trigger increased release of BVOCs.

Localized biogenic volatile organic compound emission inventory in China: A comprehensive review

Volatile organic compounds (VOCs) are the precursors of forming ozone (O3) and fine particulate matter (PM2.5). Accurate estimates of biogenic VOC (BVOC) emissions is essential for understanding the formation mechanism of O3 and PM2.5 pollution and precise reduction on anthropogenic emissions and thereby mitigating O3 and PM2.5 pollution. To gain comprehensive knowledge of BVOC emissions and improve the accuracy of their estimation, this study reviewed localized national, regional, and municipal emission estimations in China. From their comparisons, BVOC emission characteristics and deficiencies in the inventory compilation methodology were also investigated. The estimated BVOC emissions in China ranged between 10 and 58.9 Tg yr-1 and 10.9-18.9 Tg C yr-1, with diverse contributions for different BVOC categories. The simulated historical and future BVOC emissions exhibited an increasing trend. The uncertainty of the BVOC estimates was mainly from the applications of incomplete emission models, less localized accurate emission factors, deficient vegetation cover information, and low-resolution meteorological data in the inventory compilation. The regional and municipal BVOC emission inventories mainly focused on the Beijing-Tianjin-Hebei, Pearl River Delta, Sichuan Basin, and Yangtze River Delta regions, as well as the cities therein. For the same area, different studies reported diverse BVOC emissions by a maximum of two orders of magnitude. There is usually a lack of basic data with more detailed investigations and higher precision for estimation of BVOC emissions. By summarizing the measurements on terrestrial and marine BVOC emission fluxes, they are mainly focused on the Guangdong, Zhejiang and Jiangxi provinces, and Yellow Sea, East China Sea, and South China Sea, respectively. Expanding the temporal and spatial scales of observations is encouraged to enhance our understanding on the emissions and improve the emission estimates.

Spatial and species-specific responses of biogenic volatile organic compound (BVOC) emissions to elevated ozone from 2014-2020 in China

China suffered from serious and elevated ozone (O3) pollution during 2014-2020. O3 exposure increased with W126, a biologically based cumulative exposure index, at a rate of 1.738 ppm-hr yr-1. MEGAN3.1 was applied to estimate biogenic volatile organic compound (BVOC) emissions and their response to O3 pollution in China by quantifying species responses to O3 stress. In 2020, China's BVOC emissions were 23.26 Tg when considering the effects of O3 pollution, which was 1.7 % higher than that without O3 stress. Isoprene, monoterpenes, sesquiterpenes, and other VOC emissions changed by -1.0 %, 1.4 %, 15.5 %, and 2.7 %, respectively. The stimulated BVOC emissions were mainly focused on the North China Plain (NCP) and a partial area of the Tibetan Plateau, which increased by >45 %. Changes in monthly emissions differed, with the greatest increase, 181 tons (3.25 %), in August. The seasonal patterns for the impacts of O3 pollution were also distinguished spatially. The elevated O3 exposure caused BVOC emission increases of 104.7 Gg yr-1 during 2014-2020, with isoprene, monoterpenes, sesquiterpenes, and other VOCs contributing -18.6 %, 27.5 %, 40.4 %, and 50.8 %, respectively. The greatest increase in emissions appeared on the NCP and eastern and central China, with annual increases of >100 tons per grid (36 km × 36 km). The interannual variations in BVOC emissions also displayed different seasonal patterns.

Review on plant terpenoid emissions worldwide and in China

Biogenic volatile organic compounds (BVOCs), particularly terpenoids, can significantly drive the formation of ozone (O₃) and secondary organic aerosols (SOA) in the atmosphere, as well as directly or indirectly affect global climate change. Understanding their emission mechanisms and the current progress in emission measurements and estimations are essential for the accurate determination of emission characteristics, as well as for evaluating their roles in atmospheric chemistry and climate change. This review summarizes the mechanisms of terpenoid synthesis and release, biotic and abiotic factors affecting their emissions, development of emission observation techniques, and emission estimations from hundreds of published papers. We provide a review of the main observations and estimations in China, which contributes a significant proportion to the total global BVOC emissions. The review suggests the need for further research on the comprehensive effects of environmental factors on terpenoid emissions, especially soil moisture and nitrogen content, which should be quantified in emission models to improve the accuracy of estimation. In China, it is necessary to conduct more accurate measurements for local plants in different regions using the dynamic enclosure technique to establish an accurate local emission rate database for dominant tree species. This will help improve the accuracy of both national and global emission inventories. This review provides a comprehensive understanding of terpenoid emissions as well as prospects for detailed research to accurately describe terpenoid emission characteristics worldwide and in China.

Air quality change during the COVID-19 pandemic lockdown over the Auvergne-Rhône-Alpes region, France

Under the rapid spread of coronavirus diseases (COVID-19) worldwide, a complete lockdown was imposed in France from March 17th to May 11th, 2020 to limit the virus spread. This lockdown affected significantly the atmospheric pollution levels due to the restrictions of human activities. In the present study, we investigate the evolution of air quality in the Auvergne-Rhône-Alpes region, focusing on nine atmospheric pollutants (NO₂, NO, PM₁₀, PM_2.5, O₃, VOC, CO, SO₂, and isoprene). In Lyon, center of the region, the results indicated that NO₂, NO, and CO levels were reduced by 67%, 78%, and 62%, respectively, resulting in a decrease in road traffic by 80%. However, O₃, PM₁₀, and PM_2.5 were increased by 105%, 23%, and 53%, respectively, during the lockdown. The increase in ozone is explained by the dropping in NO and other gases linked to human activity, which consume ozone. Thus, the increase of solar radiation, sunshine, temperature, and humidity promoted the O₃ formation during the lockdown. Besides, rising temperature enhances the BVOC emissions such as isoprene. In addition, volatile organic component (VOC) and SO₂ remain almost stable and oxidation of these species leads to the formation of ozone and organic aerosol, which also explains the increase in PM during the lockdown. This study shows the contribution of atmospheric photochemistry to air pollution.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11869-020-00965-w.