Carbonyl Compounds Regulate Atmospheric Oxidation Capacity and Particulate Sulfur Chemistry in the Coastal Atmosphere.

Carbonyl compounds play a crucial role in the formation of ozone (O3) and secondary aerosols, with recent studies particularly highlighting formaldehyde (HCHO) as a significant contributor to the missing particulate sulfur. However, evaluations based on field observations are limited, especially in clean marine environments. Utilizing observation data from a coastal mountain site in May 2021 in Qingdao, northern China, we reveal the important regulating effect of carbonyls in atmospheric oxidation capacity and particulate sulfur chemistry using detailed chemical box models. Photolysis of gaseous carbonyls accounted for >90% and >60% of the primary sources of HO2 and RO2, respectively, contributing 38% of net O3 production. Notably, HCHO alone constituted 80% of the primary HO2 and 15% of net O3 production. Using a multiphase model with updated HCHO-related chemistry, we determine that HCHO chemistry can account for up to 30% of total particulate sulfur (the sum of hydroxymethanesulfonate and sulfate) and address more than one-third of the simulated sulfate gap. The emission-based multiphase model indicates that the HCHO-related pathway remains significant and can account for 20% of the particulate sulfur under clean marine conditions. These findings underscore the importance of carbonyls, particularly HCHO, in regulating the atmospheric oxidation capacity and particulate sulfur chemistry in the marine atmosphere, urging further laboratory studies on chemical kinetics and field measurements of particle-phase carbonyls.

Marine sources of formaldehyde in the coastal atmosphere.

Elevated concentrations of formaldehyde and other carbonyl compounds are frequently observed in the marine atmosphere but are often significantly underestimated by atmospheric models. To evaluate the potential impact of marine sources on atmospheric formaldehyde, high-resolution measurements were conducted at a coastal site (∼15 m from the sea) during the summer in Qingdao, China. Observed formaldehyde levels averaged 2.4 ± 0.9 ppbv (1 ppbv = 10-9 L L-1), with peaks reaching 6.8 ppbv. Backward trajectories indicate that formaldehyde concentrations remained high in marine air masses. Formaldehyde exhibited weak correlations with primary pollutants such as NO and CO but showed strong correlations with marine tracers, notably methyl ethyl ketone and 1-butene. Chamber experiments confirmed that the photodecomposition of Enteromorpha released large amounts of formaldehyde and marine tracer species. When normalized to acetylene, the levels of formaldehyde, 1-butene, and MEK increased by factors of 3.8, 8.1, and 3.5, respectively. Results from an observation-based chemical box model simulation, which utilizes the Master Chemical Mechanism (MCM), revealed that formaldehyde contributes 56% to the primary source of HO2 radicals, while neglecting formaldehyde chemistry would lead to a 15% reduction in coastal ozone production rates. This study interlinks oceanic biology and atmospheric chemistry, advancing the understanding of the ocean's role as a significant source of organic compounds and its contribution to carbon cycling.

Spatiotemporal Variation and Influencing Factors of TSP and Anions in Coastal Atmosphere of Zhanjiang City, China.

Water-soluble anions and suspended fine particles have negative impacts on ecosystems and human health, which is a current research hotspot. In this study, coastal suburb, coastal urban area, coastal tourist area, and coastal industrial area were explored to study the spatiotemporal variation and influencing factors of water-soluble anions and total suspended particles (TSP) in Zhanjiang atmosphere. In addition, on-site monitoring, laboratory testing, and analysis were used to identify the difference of each pollutant component at the sampling stations. The results showed that the average concentrations of Cl-, NO3-, SO42-, PO43-, and TSP were 29.8 µg/m3, 19.6 µg/m3, 45.6 µg/m3, 13.5 µg/m3, and 0.28 mg/m3, respectively. The concentration of Cl-, NO3-, PO43-, and atmospheric TSP were the highest in coastal urban area, while the concentration of SO42- was the highest in coastal industrial area. Moreover, there were significantly seasonal differences in the concentration of various pollutants (p < 0.05). Cl- and SO42- were high in summer, and NO3- and TSP were high in winter. Cl-, SO42-, PO43-, and TSP had significant correlations with meteorological elements (temperature, relative humidity, atmospheric pressure, and wind speed). Besides, the results showed the areas with the most serious air pollution were coastal urban area and coastal industrial area. Moreover, the exhaust emissions from vehicles, urban enterprise emissions, and seawater evaporation were responsible for the serious air pollution in coastal urban area. It provided baseline information for the coastal atmospheric environment quality in Zhanjiang coastal city, which was critical to the mitigation strategies for the emission sources of air pollutants in the future.

Formation of peroxyacetyl nitrate (PAN) and its impact on ozone production in the coastal atmosphere of Qingdao, North China.

Peroxyacetyl nitrate (PAN), acting as a relatively long-lived reservoir for both NOx and radicals, plays a crucial role in ozone (O3) formation in the troposphere. However, its quantitative impacts on radical concentrations and O3 production were rarely studied in the coastal atmosphere. In this study, ambient concentrations of PAN, O3, and related species were simultaneously measured from October 5 to November 10, 2018 (autumn), and July 14 to August 24, 2019 (summer) at a rural coastal site in Qingdao, North China. The formation mechanism of PAN and its impact on in-situ O3 production were explored with an observation-based chemical box model. Photochemical formation of PAN and O3 was controlled by both NOx and VOCs, and acetaldehyde and methylglyoxal were the main contributors to PAN formation. However, the sensitivities of PAN to precursors were larger than that of O3 in autumn while smaller in summer, which was mainly caused by the rapid decomposition of PAN at high temperatures. Zero-out sensitivity simulation showed that PAN could either promote or inhibit the in-situ O3 formation by affecting the radical chemistry. It tended to suppress O3 production by competing with precursors and terminating radical chain reactions under low-NOx and low-ROx circumstances but enhanced O3 production by supplying RO2 radicals under conditions with sufficient NOx. This study provides some new complementary insights into the formation mechanism of PAN and its impacts on O3 production, and has implications for the formulation of control policy to mitigate regional photochemical pollution in northern China.

Real-time non-refractory PM1 chemical composition, size distribution and source apportionment at a coastal industrial park in the Yangtze River Delta region, China.

This study present real-time measurements of the chemical composition and particle number size distributions (PNSD) of submicron particulate matter (PM1) in winter at a coastal industrial park in the Yangtze River Delta region of China. Positive matrix factorization (PMF) analysis identified three PNSD factors and three organic aerosol (OA) factors. Contributions and potential source regions of these factors were investigated for four typical periods during the PM1 formation and dissipation process. Results show that the relative contributions from aged 250 nm- factor, fresh 35 nm- and 80 nm- factors were strongly affected by local fresh emissions and regional new particle formation. The non-refractory PM1 measured by Aerodyne aerosol chemical speciation monitor is indicative of the chemical composition of aged 250 nm-factor, but not fresh 35 nm- and 80 nm-factors. The contributions of NO3- and SO42- to NR-PM1 were largely dictated by whether the air mass trajectory went over the sea or the continent. NO3- was abundant (up to 44% of NR-PM1) in cold and dry continental air masses, while SO42- formation (up to 39% of NR-PM1) was preferred in humid and warm marine air masses. Among the three OA source factors, more-oxidized oxygenated OA (MO-OOA) was the most abundant OA factor (44-66% of total OA) throughout the entire field campaign, while an enhanced contribution of 39% from hydrocarbon-like OA (HOA) was observed prior to heavy pollution period. On average, secondary components SO42-, NO3-, NH4+, MO-OOA and less-oxidized oxygenated OA (LO-OOA) contributed 90 ± 7% of NR-PM1, while primary components HOA and Cl- accounted for the remaining 10 ± 7%.

Effects of continental anthropogenic sources on organic aerosols in the coastal atmosphere of East China.

Although organic compounds in marine atmospheric aerosols have significant effects on climate and marine ecosystems, they have rarely been studied, especially in the coastal regions of East China. To assess the origins of the organic aerosols in the East China coastal atmosphere, PM2.5 samples were collected from the atmospheres of the Yellow Sea, the East China Sea, and Changdao Island during the CAPTAIN (Campaign of Air PolluTion At INshore Areas of Eastern China) field campaign in the spring of 2011. The marine atmospheric aerosol samples that were collected were grouped based on the backward trajectories of their air masses. The organic carbon concentrations in the PM2.5 samples from the marine and Changdao Island atmospheres were 5.5 ± 3.1 µgC/m3 and 6.9 ± 2.4 µgC/m3, respectively, which is higher than in other coastal water atmospheres. The concentration of polycyclic aromatic hydrocarbons (PAHs) in the marine atmospheric PM2.5 samples was 17.0 ± 20.2 ng/m3, indicating significant continental anthropogenic influences. The influences of fossil fuels and biomass burning on the composition of organic aerosols in the coastal atmosphere of East China were found to be highly dependent on the origins of the air masses. Diesel combustion had a strong impact on air masses from the Yangtze River Delta (YRD), and gasoline emissions had a more significant impact on the "North China" marine atmospheric samples. The "Northeast China" marine atmospheric samples were most impacted by biomass burning. Coal combustion contributed significantly to the compositions of all of the atmospheric samples. The proportions of secondary compounds increased as samples aged in the marine atmosphere indicating that photochemical oxidation occured during transport. Our results quantified ecosystem effects on marine atmospheric aerosols and highlighted the uncertainties that arise when modeling marine atmospheric PM2.5 without considering high spatial resolution source data and meteorological parameters.