Aerosol Nitrogen Research Articles

Insights into anthropogenic impact on atmospheric inorganic aerosols in the largest city of the Tibetan Plateau through multidimensional isotope analysis

Particulate inorganic nitrogen aerosols (PIN) significantly influence air pollution and pose health risks worldwide. Despite extensive observations on ammonium (pNH4+) and nitrate (pNO3−) aerosols in various regions, their key sources and mechanisms in the Tibetan Plateau remain poorly understood. To bridge this gap, this study conducted a sampling campaign in Lhasa, the Tibetan Plateau's largest city, with a focus on analyzing the multiple isotopic signatures (δ15N, ∆17O). These isotopes were integrated into a Bayesian mixing model to quantify the source contributions and oxidation pathways for pNH4+ and pNO3−. Our results showed that traffic was the largest contributor to pNH4+ (31.8 %), followed by livestock (25.4 %), waste (21.8 %), and fertilizer (21.0 %), underscoring the impact of vehicular emissions on urban NH3 levels in Lhasa. For pNO3−, coal combustion emerged as the largest contributor (27.3 %), succeeded by biomass burning (26.3 %), traffic emission (25.3 %), and soil emission (21.1 %). In addition, the ∆17O-based model indicated a dominant role of NO2 + OH (52.9 %) in pNO3− production in Lhasa, which was similar to previous observations. However, it should be noted that the NO3 + volatile organic component (VOC) contributed up to 18.5 % to pNO3− production, which was four times higher than the Tibetan Plateau's background regions. Taken together, the multidimensional isotope analysis performed in this study elucidates the pronounced influence of anthropogenic activities on PIN in the atmospheric environment of Lhasa.

Nitrogen aerosols in New Delhi, India: Speciation, formation, and sources

Delhi, the capital city of India, experiences severe air pollution and suffers from its adverse effects on human health and ecosystems. This pollution is characterized by high levels of pollutants, including atmospheric nitrogen in both the gaseous and particulate phases. However, there is a lack of simultaneous measurement of chemical composition, tracers and 15N data in aerosols to understand the influence of different sources on N aerosols over Delhi. Here, we measured total nitrogen (TN), water-soluble total nitrogen (WSTN), water-soluble inorganic nitrogen (WSIN), and N stable isotope compositions (δ15N) in PM2.5 samples covering the post-monsoon, winter, and summer periods of the year 2018–19. NH4+-N was the major N species, accounting for an average 58% of TN and 68% of WSIN. The temporal variations of TN, WSTN, NH4+-N, NO3−-N, and WSON showed peaks in the post-monsoon and winter seasons, exhibiting seasonality similar to PM2.5 and levoglucosan (a biomass-burning tracer) indicating their co-genetic sources. Based on the correlation analysis between δ15N and N-species, we identified two distinct secondary chemical processes: i) in an NH4+-poor atmosphere, the gas-to-particle (NH3 → NH4+) conversion and subsequent formation of NH4HSO4 was the main process controlling the 15N and nitrogen enrichments in PM2.5; whereas ii) under NH4+-rich conditions, the formation and dissociation of NH4NO3 dominated. The coupled HYSPLIT and PSCF analyses highlighted the transport and contributions of open biomass burning emissions under a northwesterly atmospheric flow during post-monsoon as well as from local biomass combustion (from cooking and heating) during winter in the city and its vicinity. Our results suggested that i) both NH4+-N and NO3−-N were mainly impacted by biomass combustion during post-monsoon and winter seasons, and ii) NO3−-N resulted of dust transport from the Thar Desert in the summer season, but not NH4+-N. Finally, we recommend that future research focuses on the study of the seasonality of atmospheric nitrogen composition using 15N data from their different sources to design tailor-made measures and policies regarding the different potential sources, combining them within a comprehensive framework to ultimately improve air quality and the living environment in Delhi.

First Online Observation of Aerosol Total Organic Nitrogen at an Urban Site: Insights Into the Emission Sources and Formation Pathways of Nitrogenous Organic Aerosols

AbstractNitrogen (N) is a constituent element of ambient organic aerosol; however, we have limited knowledge of the total quantity of organic N (ON) and its relative importance to aerosol N due to a lack of effective analytical methods for ON. Here, we report first online measurements of ON in particulate matter (PM2.5) in urban Shanghai in summer of 2021 using a newly developed aerosol nitrogen analyzer. ON accounted for an average of 25% of total aerosol N and varied in the range of 5%–64% on the hourly scale. Hourly variations identified four distinct types of ON episodes that occurred in different hours of a day. Analysis aided by concurrently measured source indicative pollutants revealed that vehicular emissions, nocturnal chemistry, daytime photochemistry or combined primary sources, and secondary chemistry could drive up ON under different day‐to‐day atmospheric conditions. Our results help bridge the knowledge gap in the emissions and formation of organic aerosol.

Dissecting the contributions of organic nitrogen aerosols to global atmospheric nitrogen deposition and implications for ecosystems

ABSTRACT Atmospheric deposition of particulate organic nitrogen (ONp) is a significant process in the global nitrogen cycle and may be pivotally important for N-limited ecosystems. However, past models largely overlooked the spatial and chemical inhomogeneity of atmospheric ONp and were thus deficient in assessing global ONp impacts. We constructed a comprehensive global model of atmospheric gaseous and particulate organic nitrogen (ON), including the latest knowledge on emissions and secondary formations. Using this model, we simulated global atmospheric ONp abundances consistent with observations. Our estimated global atmospheric ON deposition was 26 Tg N yr−1, predominantly in the form of ONp (23 Tg N yr−1) and mostly from wildfires (37%), oceans (22%) and aqueous productions (17%). Globally, ONp contributed as much as 40% to 80% of the total N deposition downwind of biomass-burning regions. Atmospheric ONp deposition thus constituted the dominant external N supply to the N-limited boreal forests, tundras and the Arctic Ocean, and its importance may be amplified in a future warming climate.

Wildfire-Derived Nitrogen Aerosols Threaten the Fragile Ecosystem in Himalayas and Tibetan Plateau.

Himalayas and Tibetan Plateau (HTP) is important for global biodiversity and regional sustainable development. While numerous studies have revealed that the ecosystem in this unique and pristine region is changing, their exact causes are still poorly understood. Here, we present a year-round (23 March 2017 to 19 March 2018) ground- and satellite-based atmospheric observation at the Qomolangma monitoring station (QOMS, 4276 m a.s.l.). Based on a comprehensive chemical and stable isotope (15N) analysis of nitrogen compounds and satellite observations, we provide unequivocal evidence that wildfire emissions in South Asia can come across the Himalayas and threaten the HTP's ecosystem. Such wildfire episodes, mostly occurring in spring (March-April), not only substantially enhanced the aerosol nitrogen concentration but also altered its composition (i.e., rendering it more bioavailable). We estimated a nitrogen deposition flux at QOMS of ∼10 kg N ha-1 yr-1, which is approximately twice the lower value of the critical load range reported for the Alpine ecosystem. Such adverse impact is particularly concerning, given the anticipated increase of wildfire activities in the future under climate change.

High contribution of anthropogenic combustion sources to atmospheric inorganic reactive nitrogen in South China evidenced by isotopes

Abstract. Due to the intense release of reactive nitrogen (Nr) from anthropogenic activity, the source layout of atmospheric nitrogen aerosol has changed. To comprehensively clarify the level, sources, and environmental fate of NH4+ and NO3-, their concentrations and stable isotopes (δ15N) in fine particulate matter (PM2.5) were measured in a subtropical megacity of South China. The inorganic nitrogen (NH4+ and NO3-) was an essential part of atmospheric nitrogen aerosol, and the N-NH4+ and N-NO3- contributed 45.8 % and 23.2 % to total nitrogen (TN), respectively. The source contributions of NH4+ and NO3- were estimated by δ15N, suggesting that the dominant sources were from anthropogenic combustion activities, including coal combustion, biomass burning, and vehicles, contributing 63.2 % and 88.3 % to NH4+ and NO3-, respectively. In particular, biomass burning was the predominant source of NH4+ (27.9 %), whereas coal combustion was the dominant source of NO3- (40.4 %). This study emphasized the substantial impacts of human activities on inorganic Nr. With the rapid development of industry and transportation, nitrogen emissions will be even higher. The promotion of clean energy and efficient use of biomass would help to reduce nitrogen emissions and alleviate air pollution.

Precipitation frequency controls nitrogenous aerosol in a tropical coastal city and its implications for plant carbon sequestration

The concentration of nitrogenous aerosols is influenced by air mass transition, local meteorological conditions, local emissions, and the wet removal effect driven by precipitation. Deposited nitrogenous aerosols influence nitrogen availability in the canopy, affecting the amount of plant carbon sequestration. However, the factors controlling nitrogenous aerosol concentrations and their implications for plant carbon sequestration remain unclear. In this study, multiple stable nitrogen isotopes in atmospheric aerosols (δ15N-TN, δ15N–NO3–, and δ15N–NH4+) and rainwater (rainwater δ15N–NO3– and rainwater δ15N–NH4+) in one-year observations were analyzed to explore the main factors controlling nitrogenous aerosol concentrations. The results showed that NO3− and NH4+ were the major components of TN, and their concentrations in seasonal patterns were sensitive to frequent rainfall rather than local emissions or external contributions. The concentrations of nitrogenous aerosols were negatively correlated with precipitation frequency, indicating that increased precipitation frequency induced low concentrations of nitrogenous aerosols. Moreover, the positive matrix factorization (PMF) analysis showed that coarse mode NO3− was generated in the wet season but not in the dry season, reflecting the removal of precipitation. With the increased precipitation frequency from May to July, 42.4% of aerosol NO3− was scavenged into rainwater, indicated by the variations in the δ15N values of nitrogenous aerosols and rainwater. This result prompted us to calculate the loss of 12.1 ± 3.9 Gg carbon/yr plant carbon sequestration. Our study suggests that nitrogenous aerosols are captured by the high precipitation frequency in tropical areas, decreasing nitrogen availability in the canopy, which might decrease plant carbon sequestration.

Marine nitrogen fixation as a possible source of atmospheric water-soluble organic nitrogen aerosols in the subtropical North Pacific

Abstract. Water-soluble organic nitrogen (WSON) in marine atmospheric aerosols affect the water solubility, acidity, and light-absorbing properties of aerosol particles, which are important parameters in assessing both the climate impact and the biogeochemical cycling of bioelements. Size-segregated aerosol and surface seawater (SSW) samples were simultaneously collected over the subtropical North Pacific to investigate the origin of WSON in the marine atmosphere. The fine-mode WSON concentration (7.5 ± 6.6 ngN m−3) at 200–240∘ E along 23∘ N, defined as the eastern North Pacific (ENP), was significantly higher than that (2.4 ± 1.9 ngN m−3) at 135–200∘ E, defined as the western North Pacific (WNP). Analysis of the stable carbon isotope ratio of water-soluble organic carbon (WSOC; δ13CWSOC) together with backward trajectory indicated that most of the observed WSON in the fine particles in the ENP originated from the ocean surface. We found positive relations among nitrogen-fixation rate, dissolved organic nitrogen (DON) in SSW, and the WSON concentrations. The result suggests that reactive nitrogen (DON and ammonium), produced and exuded by nitrogen-fixing microorganisms in SSW, contributed to the formation of WSON aerosols. This study provides new insights into the role of ocean-derived reactive nitrogen aerosols associated with marine microbial activity.

Assessing the impacts of CPM emitted from stationary sources on PM2.5 source appointment of Wuhan, China

The condensable particulate matter (CPM) emissions from stationary sources have attracted widespread attentions due to its negative environmental impacts. In this study, we collected some CPM samples from fourteen different stationary sources in Wuhan based on the US EPA Method 202 for investigating emission factors (EFs) and source profiles of the CPM, as well as its impact on source apportionment of PM2.5 (particulate matter with aerodynamic diameters ≤ 2.5 µm). The CPM mass concentrations and chemical components including water-soluble ions, elements and organic fractions in the CPM were explicitly analyzed. Our results revealed that the emission level of CPM was 0.8 to 14 times that of filterable particulate matter (FPM). The EF of CPM from coal-fired power plant was 168.91 g/t of coal, that was about 1–28 times higher than other stationary sources tested in this study. Alkanes (4 %–35 %), esters (9 %–46 %), and water-soluble ions (24 %–64 %) were dominant chemical species in the CPM, which significantly differed from that of the FPM. As such, we built a new emission inventory that included CPM and applied it to the chemical mass balance (CMB) model for source apportionment of PM2.5. The results showed that the contribution of stationary sources to PM2.5 increased from 17 % to 23 %, while the contribution of vehicle sources to PM2.5 decreased from 16 % to 11 % when considering the impact of CPM. In addition, isotope values of δ13C and δ15N in the CPM were measured to apportion the sources of carbon and nitrogen in aerosols. We found that the contributions of vehicle sources to carbon and nitrogen components in PM2.5 decreased by 3 % to 5 %, contribution of coal combustion sources increased by 6 % to 8 %, when considering the impact of CPM. Therefore, it is necessary to update emission inventory by including the CPM in further research for a greater accuracy of the source apportionment of PM2.5. This study has important implications for achieving improved air quality management via emission mitigation of CPM from stationary sources at the local, regional, and national scales.

Isotopic components and source analysis of inorganic nitrogen in coastal aerosols of the Yellow Sea

The coastal atmospheric environment is one of the most complex environments on earth. It is shaped by terrestrial, marine, and atmospheric processes and acts as an external nutrient source for coastal waters. At present, there are few observations of inorganic nitrogen isotopes of China coastal aerosols, let alone the Yellow Sea. In this study, a weekly collection of total suspended particulate aerosols was conducted on the Qianliyan Island in 2018 for the measurements of inorganic nitrogen species (NO3− and NH4+) and their isotopic ratios (δ15N-NO3−, δ18O-NO3−, and δ15N-NH4+). At the Qianliyan Island, the average NO3− and NH4+ concentrations were 2.49 ± 2.12 and 3.33 ± 2.68 μg·m−3, respectively; the average δ15N-NO3−, δ18O-NO3−, and δ15N-NH4+ were 2.4‰ ± 5.7‰, 78.7‰ ± 8.0‰, and −2.6‰ ± 6.3‰, respectively. The major nitrate formation pathways were •OH oxidation and N2O5 hydrolysis paths, and the dominant sources of inorganic nitrogen aerosols were coal combustion (29% ± 7%), marine (19% ± 15%), and fertilizer (16% ± 13%). Aerosol δ15N-NO3− and δ18O-NO3− were obviously higher in winter and lower in summer; conversely, aerosol δ15N-NH4+ was slightly higher in summer and slightly lower in winter. The difference in nitrogen sources was considered to be the best explanation for the aerosol δ15N-NO3− and δ15N-NH4+ differences between summer and winter, of which coal combustion contributed the most. The seasonal difference in nitrate formation paths was considered to be the best explanation for the difference of Qianliyan aerosol nitrate δ18O-NO3− between summer and winter. Aerosol inorganic nitrogen deposition flux was estimated to be 3.4 nmol N·m−2·s−1, which induced less than 1% to marine primary production, and aerosol inorganic nitrogen deposition, compared with N2 fixation, contributed some 80% of δ15N-NO3− depression of the summer Yellow Sea thermocline.

Chemical characterization of the water-soluble organic nitrogen in the maritime aerosol

In order to clarify the compound composition of the water-soluble organic nitrogen (WSON) in aerosols, simultaneous measurements of the WSON, free amino acids (FAA), combined amino acids (CAA), amines, and urea in the total suspended particles (TSP) were conducted at a remote coastal site located in the northern tip of Japan. About 15% of the water-soluble total nitrogen (WSTN) in the TSP was explained by the WSON, which suggests a significant contribution of the WSON to the bioavailable nitrogen in the TSP. About 22% of the WSON in the TSP can be explained by the FAA and CAA. Especially, the CAA showed about a 3.4-times higher concentration than the FAA and contributed about 17% of the WSON. The CAA would be a major compound group for the WSON in the TSP. The contribution of urea to the WSON was significant as a single compound; about 5% of the WSON in the TSP was explained by urea. In contrast, the contribution of amines to the WSON in the TSP was low. These four compound groups contributed about 29% of the WSON in the TSP. The contribution of the organic nitrogen compounds other than these four species to the WSON increased as the concentration of the WSON increased, which suggests that the high concentrations of the WSON in the TSP were significantly affected by the organic nitrogen compounds other than amino acids, amines, and urea.

Water-soluble organic nitrogen in fine aerosols over the Southern Ocean

Shipboard measurements of the water-soluble organic nitrogen (WSON) in the aerosols over the remote ocean in the Indian sector of the Southern Ocean were conducted during three summer seasons. The aims of this study were to improve our understanding of the spatiotemporal distributions and potential sources of the WSON over this oceanic region. The average concentration of the WSON in the PM2.5 obtained in this study was 4.7 ng m−3, which was within the reported values from a previous study over the Southern Ocean and lower than the reported over the lower latitude remote oceans. The average concentration ratio of the WSON/WSTN was 0.20. The WSON was an important piece of bioavailable nitrogen in the fine aerosols. The primary emission of sea salt particles was a principal source of the WSON. The temporal changes of the WSON concentrations were explained by the differences in the primary emission of sea salt particles.

Seasonal source analysis of nitrogen and carbon aerosols of PM2.5 in typical cities of Zhejiang, China

Fine particulate matter (PM2.5) significantly impacts global air quality and human health due to its smaller particle size and larger specific surface area. Nitrogen and carbon aerosols, as the main components of PM2.5, play key roles in air pollution. This study identified the sources and seasonal variation of nitrogen and carbon aerosols in PM2.5 in typical cities of Zhejiang. The annual average PM2.5 concentrations of Hangzhou (HZ), Ningbo (NB), and Huzhou (HUZ) were 39.8 ± 19.1 μg m−‍3, 40.0 ± 21.5 μg m−3, and 50.1 ± 22.6 μg m−3, respectively, which exceeded the Chinese air quality limit of 35.0 μg m−3. The results showed that the concentrations of nitrogen aerosols (NO3− and NH4+) in water-soluble inorganic ions were higher at 9.6 ± 4.6 μg m−3, 9.0 ± 4.5 μg m−3 and 11.5 ± 5.4 μg m−3 in HZ, NB and HUZ, respectively, especially in winter, accounting for over 60% of the total. The annual average δ15N values of PM2.5 were 6.2 ± 1.9‰, 6.4 ± 2.2‰ and 6.7 ± 1.9‰ in HZ, NB and HZ, respectively; the δ15N values in winter were relatively low. A Bayesian isotopic mixing model was employed to analyse the sources of nitrogen aerosols in winter; the results showed that nitrogen concentration was mainly affected by NH3 and NOX emitted by motor vehicle exhaust, coal combustion, biomass combustion, biogenic soil emissions, animal wastes and ocean evaporation (NB). In addition, the carbon component analysis of PM2.5 showed that the annual average mass concentration of TC accounted for 18.7%, 16.4% and 20.1% of PM2.5 in HZ, HUZ and NB, respectively. The same isotope model was used to analyse the sources of carbon aerosols; the results showed that carbon aerosols were mainly affected by the sources of motor vehicle exhaust, coal combustion, biomass combustion and dust. In the PM2.5 in Zhejiang, the most contributory sources of nitrogenous aerosols and carbon aerosols were motor vehicle exhaust sources.

Unraveling the sources of atmospheric organic aerosols over the Arabian Sea: Insights from the stable carbon and nitrogen isotopic composition

The isotopic composition of stable carbon (δ13C) and nitrogen (δ15N) in marine aerosols influenced by the continental outflows are useful proxies for understanding the aging and secondary formation processes. Every winter, the haze pollutants transported from South Asia significantly affect the chemical composition of marine atmospheric boundary layer of the Arabian Sea. Here, we assessed the δ13C of total carbon (TC) and δ15N of total nitrogen (TN) in marine aerosols collected over the Arabian Sea during a winter cruise (6–24 December 2018). TC (2.1–13.4 μg m−3) is strongly correlated with TN (0.9–5.0 μg m−3), likely because of their common source-emissions, biomass burning and fossil-fuel combustion in the Indo-Gangetic Plain and South Asia (corroborated by backward-air mass trajectories and satellite fire counts). Besides, the linear relationship between the mass ratios of water-soluble organic carbon (WSOC) to TC (0.04–0.65) and δ13CTC (−25.1‰ to −22.9‰) underscores the importance of aging process. This means oxidation of organic aerosols during transport not only influences the WSOC levels but also affects their δ13CTC. Likewise, the prevalent inverse linear relationship between the equivalent mass ratio of (NH4+/non-sea-salt- or nss-SO42−) and δ15NTN (+15.3‰ to +25.1‰) emphasizes the overall significance of neutralization reactions between major acidic ([nss-SO42−] ≫ [NO3−]) and alkaline species (NH4+) in aerosols. Higher δ15NTN values in winter than the spring inter-monsoon clearly emphasizes the significance of the anthropogenic combustion sources (i.e., biomass burning) in the South Asian outflow. A comparison of δ13CTC and δ15NTN with the source emissions revealed that crop-residue burning emissions followed by the coal fired power plants mostly dictate the atmospheric abundance of organic aerosols in the wider South Asian outflow.

Modelling changes in secondary inorganic aerosol formation and nitrogen deposition in Europe from 2005 to 2030

Abstract. Secondary inorganic PM2.5 particles are formed from SOx (SO2+SO42-), NOx (NO+NO2), and NH3 emissions, through the formation of either ammonium sulfate ((NH4)2SO4) or ammonium nitrate (NH4NO3). EU limits and WHO guidelines for PM2.5 levels are frequently exceeded in Europe, in particular in the winter months. In addition the critical loads for eutrophication are exceeded in most of the European continent. Further reductions in NH3 emissions and other PM precursors beyond the 2030 requirements could alleviate some of the health burden from fine particles and also reduce the deposition of nitrogen to vulnerable ecosystems. Using the regional-scale EMEP/MSC-W model, we have studied the effects of year 2030 NH3 emissions on PM2.5 concentrations and depositions of nitrogen in Europe in light of present (2017), past (2005), and future (2030) conditions. Our calculations show that in Europe the formation of PM2.5 from NH3 to a large extent is limited by the ratio between the emissions of NH3 on one hand and SOx plus NOx on the other hand. As the ratio of NH3 to SOx and NOx is increasing, the potential to further curb PM2.5 levels through reductions in NH3 emissions is decreasing. Here we show that per gram of NH3 emissions mitigated, the resulting reductions in PM2.5 levels simulated using 2030 emissions are about a factor of 2.6 lower than when 2005 emissions are used. However, this ratio is lower in winter. Thus further reductions in the NH3 emissions in winter may have similar potential to SOx and NOx in curbing PM2.5 levels in this season. Following the expected reductions of NH3 emission, depositions of reduced nitrogen (NH3+NH4+) should also decrease in Europe. However, as the reductions in NOx emission are larger than for NH3, the fraction of total nitrogen (reduced plus oxidised nitrogen) deposited as reduced nitrogen is increasing and may exceed 60 % in most of Europe by 2030. Thus the potential for future reductions in the exceedances of critical loads for eutrophication in Europe will mainly rely on the ability to reduce NH3 emissions.

Dry-deposition of inorganic and organic nitrogen aerosols in Xiamen Bay: Fluxes, sources, and biogeochemical significance

Increased dry deposition of nitrogen aerosols (aerosol-N) as a result of anthropogenic emissions has caused large negative impacts on marine ecosystems. We monitored the number concentrations and sizes of inorganic nitrogen aerosols (aerosol-IN: NH4+ and NO3−) and organic nitrogen aerosols (aerosol-ON: methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and triethylamine) by single-particle aerosol mass spectrometry (SPAMS) during the warm season (WS) and cold season (CS) of 2013 and 2015 in Xiamen Bay. The mean hourly number concentration of aerosol-IN (874/h) overwhelmed that of aerosol-ON (103/h), accounting for 83.9 ± 16.1% of aerosol-N. More than 90% of aerosol-N was concentrated in the condensation mode (0.1–0.5 μm) and droplet mode (0.5–2.0 μm). Aerosol-IN was the main contributor (80.1–94.2%) to aerosol-N deposition. New production potentially supported by the ocean's external nitrogen supply provided aerosol-N input of 11.51–11.96 g C m−2 yr−1, which contributed 17.5–18.2% of total new production in the southern East China Sea. Four potential sources of aerosol-N were identified based on the results of positive matrix factorization analysis, including secondary formation (F1), biogenic source (F2), sea spray, soil dust, biomass burning (F3), and anthropogenic sources (F4). Aerosol-N concentrations in Xiamen Bay were mainly affected by the ocean air masses during the WS and inland air masses during the CS. The percentages of aerosol-N at each backward trajectory cluster showed that the inland air masses brought more aerosol-IN emitted from biomass burning, soil dust, and secondary formation sources, whereas the ocean air masses brought more aerosol-ON emitted from a marine biogenic source into Xiamen Bay. This study provides an example of determining the number concentrations and sizes of IN and ON in aerosols by SPAMS, and helps us further understand the dry deposition and sources of IN and ON in aerosols in Xiamen Bay.

Online measurement of aerosol inorganic and organic nitrogen based on thermal evolution and chemiluminescent detection

Nitrogenous aerosols, including inorganic nitrogen (IN) and organic nitrogen (ON), are relevant to ecosystem evolution, secondary aerosol formation, and biotoxicity. While analytical method for aerosol IN species is achievable, a direct quantification method of bulk ON is so far unavailable, hindering the quantitative assessment of atmospheric nitrogenous aerosols. In this study, we develop the first online instrument method for simultaneous quantification of aerosol IN and ON. The instrument is based on programmed thermal evolution and chemiluminescent detection of nitrogenous aerosols coupled with multivariate curve resolution analysis. Atmospheric abundances of IN and ON at a suburban site in Hong Kong were quantified using the online technique, which was validated through comparing with IN measured by ion chromatography analysis of offline filters. The average mass concentrations of TN, IN, and ON were 1.84 ± 0.99, 1.59 ± 0.93, and 0.24 ± 0.09 μgN/m3, respectively. ON accounted for 13.0% of aerosol TN during the measurement period. Examination of the online IN and ON measurements during hours of aerosol nitrogen episodes revealed that biomass burning emissions and secondary formation processes could be important sources of aerosol ON. This method breakthrough enables the quantitative assessment of aerosol nitrogen at the diurnal scale, providing an effective tool to study sources and environmental impacts of nitrogenous aerosols.

Source identification and characterization of organic nitrogen in atmospheric aerosols at a suburban site in China

Despite the fact that atmospheric particulate organic nitrogen (ON) can significantly affect human health, ecosystems and the earth's climate system, qualitative and quantitative chemical characterization of ON remains limited due to its chemical complexity. In this study, the Aerodyne soot particle - high-resolution time-of-flight aerosol mass spectrometer (SP-AMS) was deployed for ambient measurements in Nanjing, China. Positive matrix factorization (PMF) was applied to the ON data to quantify the sources of ON in submicron aerosols. The averaged ON concentration was 1.24 μg m−3, while the averaged total nitrogen (TN) in the aerosol was 20.26 μg m−3. From the PMF ON analysis, a 5-factor solution was selected as the most representative and interpretable solution for the investigated dataset, including oxygenated OA (OOAON), amine-related OAON (AMOAON), hydrocarbon-like OA (HOAON), industry OA (IOAON), and local primary OA (POAON) factors. The quantified ON ions were separated into families, including CxHN, CxHyNO, C3H<6N, CxH2x+2N, CxH2xN and Others, consistent with their contribution to each factor. The CxHyNO family mainly contributed to the OOAON factor and suggested the presence of amides or amino acids. The CxH2x+2N family likely mostly originated from amines only contributing to the AMOAON and HOAON factors. The IOAON and POAON factors were resolved due to significant tracers in the mass spectra. Further, compared with regular organic PMF analysis, PMF ON analysis gave more insights due to improved source separation and interpretability of the OA components, which could be a role model for further atmospheric ON research.

Size distributions and dry deposition fluxes of water-soluble inorganic nitrogen in atmospheric aerosols in Xiamen Bay, China.

Size-segregated aerosol particles were collected using a high volume MOUDI sampler at a coastal urban site in Xiamen Bay, China, from March 2018 to June 2020 to examine the seasonal characteristics of aerosol and water-soluble inorganic ions (WSIIs) and the dry deposition of nitrogen species. During the study period, the annual average concentrations of PM1, PM2.5, PM10, and TSP were 14.8 ± 5.6, 21.1 ± 9.0, 35.4 ± 14.2 μg m−3, and 45.2 ± 21.3 μg m−3, respectively. The seasonal variations of aerosol concentrations were impacted by the monsoon with the lowest value in summer and the higher values in other seasons. For WSIIs, the annual average concentrations were 6.3 ± 3.3, 2.1 ± 1.2, 3.3 ± 1.5, and 1.6 ± 0.8 μg m−3 in PM1, PM1-2.5, PM2.5–10, and PM>10, respectively. In addition, pronounced seasonal variations of WSIIs in PM1 and PM1-2.5 were observed, with the highest concentration in spring-winter and the lowest in summer. The size distribution showed that SO42−, NH4+ and K+ were consistently present in the submicron particles while Ca2+, Mg2+, Na+ and Cl− mainly accumulated in the size range of 2.5–10 μm, reflecting their different dominant sources. In spring, fall and winter, a bimodal distribution of NO3− was observed with one peak at 2.5–10 μm and another peak at 0.44–1 μm. In summer, however, the fine mode peak disappeared, likely due to the unfavorable conditions for the formation of NH4NO3. For NH4+ and SO42−, their dominant peak at 0.25–0.44 μm in summer and fall shifted to 0.44–1 μm in spring and winter. Although the concentration of NO3–N was lower than NH4–N, the dry deposition flux of NO3–N (35.77 ± 24.49 μmol N m−2 d−1) was much higher than that of NH4–N (10.95 ± 11.89 μmol N m−2 d−1), mainly due to the larger deposition velocities of NO3–N. The contribution of sea-salt particles to the total particulate inorganic N deposition was estimated to be 23.9—52.8%. Dry deposition of particulate inorganic N accounted for 0.95% of other terrestrial N influxes. The annual total N deposition can create a new productivity of 3.55 mgC m−2 d−1, accounting for 1.3–4.7% of the primary productivity in Xiamen Bay. In light of these results, atmospheric N deposition could have a significant influence on biogeochemistry cycle of nutrients with respect to projected increase of anthropogenic emissions from mobile sources in coastal region.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10874-021-09427-8.

Chemical Characteristics, Size Distributions, Molecular Composition, and Brown Carbon in South Asian Outflow to the Indian Ocean

AbstractThe transport of South Asian (SA) anthropogenic haze to the northern Indian Ocean (NIO) is often observed during winter, however, its chemical and molecular constituents are not well explored. To better address this problem, shipborne measurements of size‐resolved aerosol sampling were carried out over the northern and equatorial Indian Ocean (EIO) for the quantification of aerosol composition (organic and inorganic) and molecular markers during the winter of 2018. The most striking outcome was the dominance of anthropogenic aerosols derived from biomass‐burning and combustion‐related emissions over the NIO during the SA outflow. Low‐level concentrations were noticed over the EIO where oceanic air mass was dominated. Organic carbon (OC), sea‐salts (Na+ and Cl−), calcium (Ca2+), and nitrates (NO3−) were enriched in the coarse mode (&gt;2.0 µm) while elemental carbon (EC), water‐soluble OC, sulfates (SO42−), and potassium (K+) were abundant in fine mode (&lt;2.0 µm) aerosols. Water‐soluble nitrogen aerosols showed a bimodal size distribution with a significant peak in fine mode. The molecular composition of organic aerosols (OAs) in PM1.1 was characterized by high abundances of sugars and lignin/resin products followed by hydroxy/polyacids and plasticizers. These results underscore that biomass‐burning emissions (BBEs), plastic combustions, and secondary anthropogenic aerosols are the leading sources of OAs in the SA outflow as further corroborated by the linear‐regression analysis between organic and inorganic marker compounds. The mass absorption efficiency (MAE) of organic (brown carbon; BrC) aerosols (MAEOC‐BrC‐365nm) was two times higher in SA outflow and largely contributed from BBEs as confirmed by the positive relationship with levoglucosan.