The stomatal compensation point of ammonia (χs) is a key factor controlling plant-atmosphere NH3 exchange, which is dependent on the nitrogen (N) supply and varies among plant species. However, knowledge gaps remain concerning the effects of elevated atmospheric N deposition and ozone (O3) on χs for forest species, resulting in large uncertainties in the parameterizations of NH3 incorporated into atmospheric chemistry and transport models (CTMs). Here, we present leaf-scale measurements of χs for hybrid poplar clone ‘546’ (Populusdeltoides cv. 55/56 x P. deltoides cv. Imperial) growing in two N treatments (N0, no N added; N50, 50 kg N ha−1 yr−1 urea fertilizer added) and two O3 treatments (CF, charcoal-filtered air; E-O3, non-filtered air plus 40 ppb) for 105 days. Our results showed that χs was significantly reduced by E-O3 (41%) and elevated N (19%). The interaction of N and O3 was significant, and N can mitigate the negative effects of O3 on χs. Elevated O3 significantly reduced the light-saturated photosynthetic rate (Asat) and chlorophyll (Chl) content and significantly increased intercellular CO2 concentrations (Ci), but had no significant effect on stomatal conductance (gs). By contrast, elevated N did not significantly affect all measured photosynthetic parameters. Overall, χs was significantly and positively correlated with Asat, gs and Chl, whereas a significant and negative relationship was observed between χs and Ci. Our results suggest that O3-induced changes in Asat, Ci and Chl may affect χs. Our findings provide a scientific basis for optimizing parameterizations of χs in CTMs in response to environmental change factors (i.e., elevated N deposition and/or O3) in the future.

Air pollutant levels depend on emissions but can also be affected by the meteorological situation. We examined air pollutant trends (PM₁₀, NO₂, O₃ and SO₂) in Slovenia, where in the past the main issue were SO₂ levels. Now, the population is still exposed to PM₁₀ and ozone levels that are above the recommended levels.Our goal was to assess if the levels of air pollutants were decreasing from 2002 to 2017 due to emission ceilings or were more influenced by changes in the meteorological situation. We modelled the relationship between levels, meteorological parameters, and seasonality and then used the models with the best estimated generalisation to adjust levels for meteorology. Models showed a significant relationship between meteorological parameters and PM₁₀, NO₂, and O₃ levels, but not SO₂. We analysed trends of raw and adjusted levels and compared them. Trends of PM₁₀ and SO₂ were decreasing at all locations for raw and adjusted data. The largest decrease was observed in SO₂ levels where the largest decrease in emissions occurred. Trends of NO₂ were also significant and negative at most locations. Levels of O₃ did not exhibit a significant trend at most locations.Results show that changes in the meteorological situation affected PM₁₀ levels the most, especially where the entire period (2002–2017) could be observed. There is strong empirical evidence that changes in meteorological parameters contributed to the decrease in PM₁₀ levels while the decrease in NO₂ and SO₂ levels can be attributed to emission ceilings.

Ozone (O₃) and nitrogen dioxide (NO₂) are thought to play primary roles in aggravating air pollution-induced health problems. However, the effects of joint O₃/NO₂ on the allergenicity of pollen allergens are unclear. Humulus japonicus pollen allergen 1 (Hum j1) is a profilin protein that causes widespread pollinosis in eastern Asia. In order to study the effects of combined O₃/NO₂ on the allergenicity of Hum j1, tandem six-histidine peptide tag (His6)-fused recombinant Hum j1 (rHum j1) was expressed in a prokaryotic system and purified through His6 affinity chromatography. The purified rHum j1 was used to immunize SD rats. Rat sera with high titers of IgG and IgE antibodies against rHum j1 were used for allergenicity quantification. The rHum j1 was exposed to O₃/NO₂, and changes in allergenicity of the exposed rHum j1 were assayed using the immunized rat antibodies. Tandem LC-MS/LC (liquid chromatography-mass spectrometer/liquid chromatography spectrometer) chromatography and UV and circular dichroism (CD) spectroscopy were used to study the structural changes in rHum j1. Our data demonstrated that a novel disulfide bond between the sulfhydryl groups of two neighboring cysteine molecules was formed after the rHum j1 exposure to joint O₃/NO₂, and therefore IgE-binding affinity was increased and the allergenicity was reinforced. Our results provided clues to elucidate the mechanism behind air pollution-induced increase in pollinosis prevalence.

Gasoline vehicles are a major source of anthropogenic secondary organic aerosols (SOAs). However, current models based on known precursors fail to explain the substantial SOAs from vehicle emissions due to the inadequate understanding of the formation mechanism. To provide more information on this issue, the formation of SOAs from ozonolysis of four light-duty gasoline vehicle exhaust systems was investigated with a vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS). Remarkable SOAs formation was observed and the SOAs were primarily aliphatic alkenes. PI mass spectra of the SOAs from all vehicles exhibited similar spectral patterns (a regular mass group with m/z at 98, 112, 126 …). Interestingly, most carbonyl products of aliphatic alkenes observed as major gaseous products have specific molecular weights, and the main formation pathway of SOAs can be explained well using aldol condensation reactions of these carbonyls. This is a direct observation of the aldol condensation as a dominated pathway for SOAs formation, and the first report on the composition and formation mechanism of the SOAs from the ozonolysis of gasoline vehicle exhaust is given. The study reveals that low molecular weight alkenes may play a more significant role in vehicle-induced SOAs formation than previously believed. More importantly, the PI mass spectra of SOAs from vehicles show similarities to the field aerosol sample mass spectra, suggesting the possible significance of the aldol condensation reactions in ambient aerosol formation. Since carbonyls are a major degradation product of biogenic and anthropogenic VOCs through atmospheric oxidation processes, the mechanism proposed in this study can be applied more generally to explain aerosol formation from the oxidation of atmospheric hydrocarbons.

In Mediterranean areas, dry deposition is a major component of the total atmospheric N input to natural habitats, particularly to forest ecosystems. An innovative approach, combining the empirical inferential method (EIM) for surface deposition of NO₃⁻ and NH₄⁺ with stomatal uptake of NH₃, HNO₃ and NO₂ derived from the DO₃SE (Deposition of Ozone and Stomatal Exchange) model, was used to estimate total dry deposition of inorganic N air pollutants in four holm oak forests under Mediterranean conditions in Spain. The estimated total deposition varied among the sites and matched the geographical patterns previously found in model estimates: higher deposition was determined at the northern site (28.9 kg N ha⁻¹ year⁻¹) and at the northeastern sites (17.8 and 12.5 kg N ha⁻¹ year⁻¹) than at the central-Spain site (9.4 kg N ha⁻¹ year⁻¹). On average, the estimated dry deposition of atmospheric N represented 77% ± 2% of the total deposition of N, of which surface deposition of gaseous and particulate atmospheric N averaged 10.0 ± 2.9 kg N ha⁻¹ year⁻¹ for the four sites (58% of the total deposition), and stomatal deposition of N gases averaged 3.3 ± 0.8 kg N ha⁻¹ year⁻¹ (19% of the total deposition). Deposition of atmospheric inorganic N was dominated by the surface deposition of oxidized N in all the forests (means of 54% and 42% of the dry and total deposition, respectively). The relative contribution of NO₂ to dry deposition averaged from 19% in the peri-urban forests to 11% in the most natural site. During the monitoring period, the empirical critical loads provisionally proposed for ecosystem protection (10–20 kg N ha⁻¹ year⁻¹) was exceeded in three of the four studied forests.

Ground-level ozone (O3) concentrations have been elevating in the last century. While there has been a notable progress in understanding O3 effects on vegetation, O3 effects on ecological stoichiometry remain unclear, especially early in the oxidative stress. Ethyelenediurea (EDU) is a chemical compound widely applied in research projects as protectant of plants against O3 injury, however its mode of action remains unclear. To investigate O3 and EDU effects early in the stress, we sprayed willow (Salix sachalinensis) plants with 0, 200 or 400 mg EDU L−1, and exposed them to either low ambient O3 (AOZ) or elevated O3 (EOZ) levels during the daytime, for about one month, in a free air O3 controlled exposure (FACE); EDU treatment was repeated every nine days. We collected samples for analyses from basal, top, and shed leaves, before leaves develop visible O3 symptoms. We found that O3 altered the ecological stoichiometry, including impacts in nutrient resorption efficiency, early in the stress. The relation between P content and Fe content seemed to have a critical role in maintaining homeostasis in an effort to prevent O3-induced damage. Photosynthetic pigments and P content appeared to play an important role in EDU mode of action. This study provides novel insights on the stress biology which are of ecological and toxicological importance.

In recent years, air pollution events have occurred frequently in China during the winter. Most studies have focused on the physical and chemical composition of polluted air. Some studies have examined the bacterial bioaerosols both indoors and outdoors. But few studies have focused on the relationship between air pollution and bacteria, especially pathogenic bacteria. Airborne PM samples with different diameters and different air quality index values were collected in Hangzhou, China from December 2014 to January 2015. High-throughput sequencing of 16S rRNA was used to categorize the airborne bacteria. Based on the NCBI database, the “Human Pathogen Database” was established, which is related to human health. Among all the PM samples, the diversity and concentration of total bacteria were lowest in the moderately or heavily polluted air. However, in the PM2.5 and PM10 samples, the relative abundances of pathogenic bacteria were highest in the heavily and moderately polluted air respectively. Considering the PM samples with different particle sizes, the diversities of total bacteria and the proportion of pathogenic bacteria in the PM10 samples were different from those in the PM2.5 and TSP samples. The composition of PM samples with different sizes range may be responsible for the variances. The relative humidity, carbon monoxide and ozone concentrations were the main factors, which affected the diversity of total bacteria and the proportion of pathogenic bacteria. Among the different environmental samples, the compositions of the total bacteria were very similar in all the airborne PM samples, but different from those in the water, surface soil, and ground dust samples. Which may be attributed to that the long-distance transport of the airflow may influence the composition of the airborne bacteria. This study of the pathogenic bacteria in airborne PM samples can provide a reference for environmental and public health researchers.

Pollen allergy risk is modified by air pollutants, including ozone, but the chemical modifications induced on pollen grains are poorly understood. Pollen lipidic extract has been shown to act as an adjuvant to the allergenic reaction and therefore, the modification of lipids by air pollutants could have health implications. Birch pollen was exposed in vitro to ozone to explore the reactivity of O₃ on its surface and on its lipidic fraction. Uptake coefficients of ozone were determined for ozone concentration of 117 ppb on the surface of native birch pollen (8.6 ± 0.8 × 10⁻⁶), defatted pollen (9.9 ± 0.9 × 10⁻⁶), and for crushed pollen grains (34±3 × 10⁻⁶). The mass of ozone uptaken was increased by a factor of four for crushed pollen compared to native pollen showing a higher susceptibility to ozone of cytoplasmic granules and broken pollen grains. A total mass of extractible lipids of 27 mg per gram of birch pollen was found and a fraction of these lipids was identified and quantified (fatty acids, alkanes, alkenes and aldehydes). The distribution of lipids was modified by ozone exposure of 115 and 1000 ppb for 16 h with the following reactivity: consumption of alkene, formation of aldehydes and formation of nonanoic acid and octadecanoic acid. The quantity of ozone trapped in the lipidic fraction during 15 min at 115 ppb is enough to contribute to the reactivity of one-third of the alkenes demonstrating that pollen could be susceptible to an atmospheric increase of ozone concentration even for a very short duration complicating the understanding of the link between pollen allergy and pollution.

In this study, concentrations of NOₓ, SO₂, O₃ and fine particles (PM₂.₅) were measured at three monitoring stations in Beijing during 2015. For extreme haze episodes during 25 Nov. - 3 Dec. 2015, observation data confirmed that high concentrations of NOₓ promoted the conversion of SO₂ to sulfate. Annual data confirmed that this is an important mechanism for the occurrence of heavy haze during winter in Beijing. Furthermore, in situ perturbation experiments in a potential aerosol mass (PAM) reactor were carried out at Shengtaizhongxin (STZX) station during both clean and polluted days. The concentrations of SO₄²⁻, NH₄⁺, NO₃⁻ and organic aerosol were positively related to the concentration of added NO₂. These results provide definitive evidence that NO₂ can promote the conversion of SO₂ to sulfate. At the same time, we found that NO₂ can promote the formation of NH₄⁺ and organic compounds in the aerosols. Our results illustrate that strengthened controls of nitrogen oxides is a key step in reducing the fine particles level in China.

Assessing ozone (O3) risk to vegetation is crucial for informing policy making. Soil nitrogen (N) and phosphorus (P) availability could change stomatal conductance which is the main driver of O3 uptake into a leaf. In addition, the availability of N and P could influence photosynthesis and growth. We thus postulated that the sensitivity of plants to O3 may be changed by the levels of N and P in the soil. In this study, a sensitive poplar clone (Oxford) was subject to two N levels (N0, 0 kg N ha−1; N80, 80 kg N ha−1), three P levels (P0, 0 kg P ha−1; P40, 40 kg P ha−1; P80, 80 kg P ha−1) and three levels of O3 exposure (ambient concentration, AA; 1.5 × AA; 2.0 × AA) for a whole growing season in an O3 free air controlled exposure (FACE) facility. Flux-based (POD0 to 6) and exposure-based (W126 and AOT40) dose-response relationships were fitted and critical levels (CLs) were estimated for a 5% decrease of total annual biomass. It was found that N and P availability modified the dose-response relationships of biomass responses to O3. Overall, the N supply decreased the O3 CLs i.e. increased the sensitivity of poplar to O3. Phosphorus alleviated the O3-caused biomass loss and increased the CL. However, such mitigation effects of P were found only in low N and not in high N conditions. In each nutritional treatment, similar performance was found between flux-based and exposure-based indices. However, the flux-based approach was superior, as compared to exposure indices, to explain the biomass reduction when all nutritional treatments were pooled together. The best O3 metric for risk assessments was POD4, with 4.6 mmol m−2 POD4 as a suitable CL for Oxford poplars grown under various soil N and P conditions.