Diverging trends in aerosol sulfate and nitrate measured in the remote North Atlantic in Barbados are attributed to clean air policies, African smoke, and anthropogenic emissions

Sulfate and nitrate aerosols degrade air quality, modulate radiative forcing and the hydrological cycle, and affect biogeochemical cycles, yet their global cycles are poorly understood. Here, we examined trends in 21 years of aerosol measurements made at Ragged Point, Barbados, the easternmost promontory on the island located in the eastern Caribbean Basin. Though the site has historically been used to characterize African dust transport, here we focused on changes in nitrate and non-sea-salt (nss) sulfate aerosols from 1990-2011. Nitrate aerosol concentrations averaged over the entire period were stable at 0.59 μg m-3 ± 0.04 μg m-3, except for elevated nitrate concentrations in the spring of 2010 and during the summer and fall of 2008 due to the transport of biomass burning emissions from both northern and southern Africa to our site. In contrast, from 1990 to 2000, nss-sulfate decreased 30% at a rate of 0.023 μg m-3 yr-1, a trend which we attribute to air quality policies enacted in the United States (US) and Europe. From 2000-2011, sulfate gradually increased at a rate of 0.021 μg m-3 yr-1 to pre-1990s levels of 0.90 μg m-3. We used the Community Multiscale Air Quality (CMAQ) model simulations from the EPA's Air QUAlity TimE Series (EQUATES) to better understand the changes in nss-sulfate after 2000. The model simulations estimate that increases in anthropogenic emissions from Africa explain the increase in nss-sulfate observed in Barbados. Our results highlight the need to better constrain emissions from developing countries and to assess their impact on aerosol burdens in remote source regions.

Remote Aerosol Simulated During the Atmospheric Tomography (ATom) Campaign and Implications for Aerosol Lifetime

We investigate and assess how well a global chemical transport model (GEOS-Chem) simulates submicron aerosol mass concentrations in the remote troposphere. The simulated speciated aerosol (organic aerosol (OA), black carbon, sulfate, nitrate, and ammonium) mass concentrations are evaluated against airborne observations made during all four seasons of the NASA Atmospheric Tomography Mission (ATom) deployments over the remote Pacific and Atlantic Oceans. Such measurements over pristine environments offer fresh insights into the spatial (Northern [NH] and Southern Hemispheres [SH], Atlantic, and Pacific Oceans) and temporal (all seasons) variability in aerosol composition and lifetime, away from continental sources. The model captures the dominance of fine OA and sulfate aerosol mass concentrations in all seasons. There is a high bias across all species in the ATom-2 (NH winter) simulations; implementing recent updates to the wet scavenging parameterization improves our simulations, eliminating the large ATom-2 (NH winter) bias, improving the ATom-1 (NH summer) and ATom-3 (NH fall) simulations, but producing a model underestimate in aerosol mass concentrations for the ATom-4 (NH spring) simulations. Following the wet scavenging updates, simulated global annual mean aerosol lifetimes vary from 1.9 to 4.0 days, depending on species. Aerosol lifetimes in each hemisphere vary by season, and are longest for carbonaceous aerosol during the southern hemispheric fire season. The updated wet scavenging parameterization brings simulated concentrations closer to observations and reduces global aerosol lifetime for all species, indicating the sensitivity of global aerosol lifetime and burden to wet removal processes.

Particulate Matter Ionic and Elemental Composition during the Winter Season: A Comparative Study among Rural, Urban and Remote Sites in Southern Italy

We present an overview of the concentrations and distributions of water-soluble ion species and elemental components in ambient particulate matter for five measurement sites in southern Italy with the aim of investigating the influence of the different site characteristics on PM levels. The sites encompass different characteristics, ranging from urban to coastal and high-altitude remote areas. PM10 and PM2.5 fractions were collected simultaneously using dual channel samplers during the winter period from November 2015 to January 2016 and analyzed for water-soluble ion species, using ion chromatography, and elemental composition, using inductively coupled plasma mass spectrometry (ICP-MS). In all sites, PM2.5 represented the higher contribution to particulate mass, usually more than two times that of the coarse fraction (PM2.5−10). At the coastal site in Capo Granitola (Western Sicily), sea salts constituted about 30% of total PM10 mass. On average, ion species accounted for 30% to 60% of total PM10 mass and 15% to 50% of PM2.5 mass. We found that secondary ion species, i.e., SO42−, NO3− and NH4+ dominated the identifiable components within both PM2.5 and PM10 fractions. The chlorine–sodium ratio was usually lower than that expected from the natural level in sea salt, evidencing aged air masses. At the monitoring site in Naples, a highly urbanized area affected by high levels of anthropogenic source emissions, an increased contribution of ammonium was found, which was imputed to the increased ammonia emissions from industrial combustion sources and road traffic. The concentrations of the investigated elements showed noteworthy differences from one site to another. The PM10 fraction was highly enriched by sources of anthropogenic origin in the samples from the most urbanized areas. In general, the enrichment factors of the elements were similar between the PM10 and PM2.5 fractions, confirming common sources for all elements.

Characteristics of ambient ammonia and its effects on particulate ammonium in winter of urban Beijing, China

To understand the characteristics of winter fine aerosol pollution in Beijing, we conducted continuous measurements of the atmospheric trace gas ammonia (NH3), PM2.5, and inorganic ions in PM2.5 at an urban site in Beijing from February 13 to March 17, 2015. The hourly average concentration of NH3 throughout the campaign was 15.4 ± 17.5 ppb. NH3 concentrations correlated well with NH4+ in PM2.5, indicating the dominant precursor role of NH3 on NH4+ formation. The diurnal profile indicated an increase in NH3 concentrations during the morning rush hours, which was likely due to vehicle emissions. The mean ammonium conversion ratio (NHR) was 0.26, with the highest value of 0.32 in the afternoon. Elevated NHR, nitrate oxidation ratio (NOR), and NH4+ coincided with the significant increase in O3 levels in the afternoon, indicating the large daytime formation of NH4NO3 via photochemical reactions. Moreover, higher NHR values occurred under higher relative humidity (RH >60%) and lower temperature (0-10 °C). NHR increased during the nighttime and correlated well with RH, indicating the dominant role of heterogeneous reactions on gas-particle partitioning. The sulfate oxidation ratio (SOR) and NOR showed positive correlations with RH, which suggests that the conversions of SO2 to SO42- and NO2 to NO3- were sensitive to changes in RH. The sustained increase in SO42- concentrations at RH >60% suggests that RH had a higher influence on SO42- formation than on NO3- formation. As the sole precursor of NH4+, NH3 significantly enhanced daytime NH4NO3 formation via homogeneous gas-phase reactions and also promoted sulfate formation via both homogeneous and heterogeneous reactions. Moreover, the back trajectory results inferred a high contribution of southwestern air masses to atmospheric NH3 and NH4+ aerosol variations in Beijing. The result suggests the need for controlling the vehicle emissions to reduce the high levels of NH3 and alleviate PM2.5 pollution in winter in Beijing.

Effects of COVID-19 lockdowns on fine particulate matter concentrations

Lockdowns during the COVID-19 pandemic provide an unprecedented opportunity to examine the effects of human activity on air quality. The effects on fine particulate matter (PM2.5) are of particular interest, as PM2.5 is the leading environmental risk factor for mortality globally. We map global PM2.5 concentrations for January to April 2020 with a focus on China, Europe, and North America using a combination of satellite data, simulation, and ground-based observations. We examine PM2.5 concentrations during lockdown periods in 2020 compared to the same periods in 2018 to 2019. We find changes in population-weighted mean PM2.5 concentrations during the lockdowns of -11 to -15 μg/m3 across China, +1 to -2 μg/m3 across Europe, and 0 to -2 μg/m3 across North America. We explain these changes through a combination of meteorology and emission reductions, mostly due to transportation. This work demonstrates regional differences in the sensitivity of PM2.5 to emission sources.

Source contribution and origin of PM10 and arsenic in a complex industrial region (Huelva, SW Spain)

Air pollution coming from industrial activities is a matter of interest since their emissions can seriously affect to the human health of nearby populations. A more detailed study about industrial emissions is required in order to discriminate different activities contributing to pollutant sources. In this sense, gaseous pollutants (NO₂, SO₂ and O₃) and PM10 levels has been studied in a complex industrial area in the southwest of Spain (La Rabida and the nearby city of Huelva) during the period 1996-2017. Hourly, daily, monthly and annual variations of PM10 and gaseous pollutants concentrations point to the industrial activity as the main SO₂ source. Furthermore, traffic and resuspension emissions contribute to the NO₂ and PM10 levels, respectively. Results from chemical composition of PM10 at both sites during the period 2015-2017 are characterized by high concentrations of the crustal components derived from natural and local resuspension. Arsenic is found to be the main geochemical anomaly at La Rabida (annual mean of 7 ng m^-3), exceeding the European annual target of 6 ng m^-3, which supposes a risk for the nearby population. An emission source from Cu-smelter has been identified in La Rabida and Huelva. A second source corresponding to emissions from polymetallic sulfides handling in a port area has been described for the first time in La Rabida. In addition, arsenic speciation results have identified three different As impacts scenarios as a function of the dominant wind direction, the SO₂ episodes and the As extraction efficiency: impact of the Cu-smelter, impact of the bulk polymetallic sulfides and a mixed impact of both sources.

Development and Evaluation of Chemistry-Aerosol-Climate Model CAM5-Chem-MAM7-MOSAIC: Global Atmospheric Distribution and Radiative Effects of Nitrate Aerosol

An advanced aerosol treatment, with a focus on semivolatile nitrate formation, is introduced into the Community Atmosphere Model version 5 with interactive chemistry (CAM5-chem) by coupling the Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) with the 7-mode Modal Aerosol Module (MAM7). An important feature of MOSAIC is dynamic partitioning of all condensable gases to the different fine and coarse mode aerosols, as governed by mode-resolved thermodynamics and heterogeneous chemical reactions. Applied in the free-running mode from 1995 to 2005 with prescribed historical climatological conditions, the model simulates global distributions of sulfate, nitrate, and ammonium in good agreement with observations and previous studies. Inclusion of nitrate resulted in ∼10% higher global average accumulation mode number concentrations, indicating enhanced growth of Aitken mode aerosols from nitrate formation. While the simulated accumulation mode nitrate burdens are high over the anthropogenic source regions, the sea-salt and dust modes respectively constitute about 74% and 17% of the annual global average nitrate burden. Regional clear-sky shortwave radiative cooling of up to -5 W m-2 due to nitrate is seen, with a much smaller global average cooling of -0.05 W m-2. Significant enhancements in regional cloud condensation nuclei (at 0.1% supersaturation) and cloud droplet number concentrations are also attributed to nitrate, causing an additional global average shortwave cooling of -0.8 W m-2. Taking into consideration of changes in both longwave and shortwave radiation under all-sky conditions, the net change in the top of the atmosphere radiative fluxes induced by including nitrate aerosol is -0.7 W m-2.

Multicomponent diffusion in atmospheric aerosol particles

Condensed phase mass transport in single aerosol particles is investigated using a linear quadrupole electrodynamic balance (LQ-EDB) and the Maxwell–Stefan (MS) framework.

Sources of gaseous NH3 in urban Beijing from parallel sampling of NH3 and NH4+, their nitrogen isotope measurement and modeling

Atmospheric gaseous ammonia (NH₃) is the most abundant alkaline gas in the atmosphere while aerosol ammonium (NH₄⁺) constitutes a majority of the inorganic cation concentration in total PM_2.5 mass and plays a vital role in severe haze formation. This study tried to shed some light on sources of gaseous NH₃ through integrating the parallel measurements of δ¹⁵N values in NH₄⁺ and ambient NH₃, NH₃ source signature measurement, IsoSource model, and chemistry and transport model (CTM). As a result, predicted initial δ¹⁵N (NH₃) values ranging from -42.0‰ to -4.9‰ were derived from daily δ¹⁵N(NH₄⁺) values of fine particulate NH₄⁺, and δ¹⁵N(NH₃) values ranging from -26.8‰ to -17.2‰ were obtained from weekday/weekend δ¹⁵N(NH₃) values, respectively. During summer, non-agricultural sources (e.g. fossil fuel sources, urban waste) contributed 63% to ambient NH₃ in urban Beijing, derived from δ¹⁵N(NH₃) values whereas 64% to ambient NH₃, derived from δ¹⁵N(NH₄⁺) values. These results suggested that non-agricultural sources were main contributors to gaseous NH₃ even during summer and agricultural sources were not likely the main source of gaseous NH₃ in urban Beijing. To further reduce the uncertainty of isotope-based source apportionment results, more laboratory and field studies are necessary to refine the δ¹⁵N(NH₃) source profile of NH₃ using validated collection technique as overlapping exist between δ¹⁵N(NH₃) values in agricultural sources such as livestock breeding waste (-42.5‰ to -29.1‰) and fertilizer application (-51.5‰ to -35.0‰).

Quantification of Atmospheric Ammonia Concentrations: A Review of Its Measurement and Modeling

Ammonia (NH3), the most prevalent alkaline gas in the atmosphere, plays a significant role in PM2.5 formation, atmospheric chemistry, and new particle formation. This paper reviews quantification of [NH3] through measurements, satellite-remote-sensing, and modeling reported in over 500 publications towards synthesizing the current knowledge of [NH3], focusing on spatiotemporal variations, controlling processes, and quantification issues. Most measurements are through regional passive sampler networks. [NH3] hotspots are typically over agricultural regions, such as the Midwest US and the North China Plain, with elevated concentrations reaching monthly averages of 20 and 74 ppbv, respectively. Topographical effects dramatically increase [NH3] over the Indo-Gangetic Plains, North India and San Joaquin Valley, US. Measurements are sparse over oceans, where [NH3] ≈ a few tens of pptv, variations of which can affect aerosol formation. Satellite remote-sensing (AIRS, CrIS, IASI, TANSO-FTS, TES) provides global [NH3] quantification in the column and at the surface since 2002. Modeling is crucial for improving understanding of NH3 chemistry and transport, its spatiotemporal variations, source apportionment, exploring physicochemical mechanisms, and predicting future scenarios. GEOS-Chem (global) and FRAME (UK) models are commonly applied for this. A synergistic approach of measurements↔satellite-inference↔modeling is needed towards improved understanding of atmospheric ammonia, which is of concern from the standpoint of human health and the ecosystem.

Secondary aerosol formation and its linkage with synoptic conditions during winter haze pollution over eastern China

Eastern China has been facing severe winter haze pollution due mainly to secondary aerosol. Existing studies have suggested that stagnant weather or fast chemical production led to frequent haze in this region. However, few works focus on the linkage between secondary production of sulfate, nitrate, and ammonium (SNA) and synoptic conditions, and their joint contribution to PM_2.5. In this study, by combining in-situ measurements on meteorology and aerosol chemical composition at three main cities together with a regional model with improved diagnose scheme, we investigated the chemical formation and accumulation of main secondary composition, i.e. SNA under typical synoptic conditions. It is indicated that SNA did play a vital role in haze pollution across eastern China, contributing more than 40% to PM_2.5 mass concentration. As most fast developing region, the Yangtze River Delta (YRD) was slightly polluted during stable weather with local chemical production accounting for 61% SNA pollution. While under the influence of cold front, the pollution was aggravated and advection transport became the predominant contributive process (85%). Nevertheless, the chemical production of SNA was notably enhanced due to the uplift of air pollutant and elevated humidity ahead of the cold front, which then facilitated the heterogeneous and aqueous-phase oxidation of precursors. We also found the substantial difference in the phase equilibrium of nitrate over the land surface and ocean due to changes in temperature, ammonia availability and dry deposition. This study highlights the close link between synoptic weather and chemical production, and the resultant vertical and spatial heterogeneity of pollution.

Chemical and isotopic characteristics of PM10 over the Bay of Bengal: Effects of continental outflow on a marine environment

Pollutants transport from South and Southeast Asia can profoundly affect the marine atmospheric boundary layer (MABL) over the Bay of Bengal (BoB). This study presents chemical and stable isotopic composition of PM₁₀ collected at Port Blair Island (11.6°N, 92.7°E) located in the middle of the BoB during the late northeast monsoon (February-April), a period when the BoB receives considerable continental outflow. These samples (n = 50) were analysed for major ions, carbonaceous species, trace metals, and isotopic composition of total C, N, and S components. Mass concentration of PM₁₀ ranged from 24 to 65 μg m^-3 during the study period. The dominance of continental inputs over a marine realm was evident by a significant amount of non-sea-salt (nss)-SO₄^2- (range: 1.8 to 16.9 μg m^-3), which accounts for ~65% of the total water-soluble inorganic constituents. The impact of anthropogenic emissions was further evident from the widespread depletion of chloride (range: 57-100%, avg.: 98 ± 7%) from sea-salt aerosols. Carbonaceous species (elemental carbon and organic matter) contributed nearly 35% to PM₁₀. Further, average δ¹³C (-25.6‰ ± 0.5) and δ³⁴S (4.5‰ ± 1.3) values observed over the marine study region were similar to those found in typical urban environments. δ¹⁵N values (13.7‰ ± 5.1) show the significant presence of combustion sources along with the effect of atmospheric processing. Aerosol δ¹³C values correlate positively with the ratio of water-soluble organic carbon to total organic carbon, indicating the aging of organic aerosols during the transport. Chemical and isotopic data suggest that both biomass burning (BB) and fossil fuel burning (FFB) contributed to ambient PM₁₀ with relatively more contribution of BB during February to early March and that of FFB during late March to middle of April. In aggregate, this study provides newer insights into sources of carbonaceous species and their chemical processing in MABL of BoB.

The Acidity of Atmospheric Particles and Clouds

Acidity, defined as pH, is a central component of aqueous chemistry. In the atmosphere, the acidity of condensed phases (aerosol particles, cloud water, and fog droplets) governs the phase partitioning of semi-volatile gases such as HNO3, NH3, HCl, and organic acids and bases as well as chemical reaction rates. It has implications for the atmospheric lifetime of pollutants, deposition, and human health. Despite its fundamental role in atmospheric processes, only recently has this field seen a growth in the number of studies on particle acidity. Even with this growth, many fine particle pH estimates must be based on thermodynamic model calculations since no operational techniques exist for direct measurements. Current information indicates acidic fine particles are ubiquitous, but observationally-constrained pH estimates are limited in spatial and temporal coverage. Clouds and fogs are also generally acidic, but to a lesser degree than particles, and have a range of pH that is quite sensitive to anthropogenic emissions of sulfur and nitrogen oxides, as well as ambient ammonia. Historical measurements indicate that cloud and fog droplet pH has changed in recent decades in response to controls on anthropogenic emissions, while the limited trend data for aerosol particles indicates acidity may be relatively constant due to the semi-volatile nature of the key acids and bases and buffering in particles. This paper reviews and synthesizes the current state of knowledge on the acidity of atmospheric condensed phases, specifically particles and cloud droplets. It includes recommendations for estimating acidity and pH, standard nomenclature, a synthesis of current pH estimates based on observations, and new model calculations on the local and global scale.

Characteristics of indoor and outdoor fine particles in heating period at urban, suburban, and rural sites in Harbin, China

Concurrent indoor-outdoor fine particulate matter (PM_2.5) measurements were conducted at urban, suburban, and rural sites in Harbin, a megacity in the northeast of China. Chemical constituents of indoor-outdoor PM_2.5 were determined. Infiltration factors (F_INF) of all sites were calculated according to the indoor to outdoor (I/O) ratios of PM_2.5 based on the regression analysis. Linear discriminant analysis (LDA) is applied to determine the indoor-outdoor relationship. Secondary organic carbon (SOC) was calculated on the basis of organic carbon to elemental carbon (OC/EC) ratios. The mean concentrations of indoor and outdoor PM_2.5 were 166.4 ± 32.5 μg/m³ and 228.4 ± 83.7 μg/m³, respectively, during the heating period. OC/EC and potassium ion to elemental carbon (K⁺/EC) ratios verified that biomass was an important source in Harbin especially for rural sites. The nitrate to sulfate (NO₃^-/SO₄^2-) ratio indicates the higher contribution of traffic emissions in urban sites. Cr was the only species that exceeded the guidelines of WHO 2002, which was mainly emitted from coal and oil combustion. SOC/OC and NO₃^-/SO₄^2- ratios, and ion-balanced acidity (the ratio of cation to anion, R_+/-) showed a large urban-rural and indoor-outdoor difference. The highest SOC/OC ratio was found at urban sites, up to 38.3% for indoors. SOC/OC ratios and R_+/- values of indoor environments were higher, which is attributed to the conducive condition of forming the secondary pollutants during the heating period. The results of LDA indicated that the distributions of the chemical components of PM_2.5 at three sites were statistically dissimilar. Graphical abstract.

Atmospheric Dry Deposition of Water-Soluble Nitrogen to the Subarctic Western North Pacific Ocean during Summer

To estimate dry deposition flux of atmospheric water-soluble nitrogen (N), including ammonium (NH4+), nitrate (NO3−), and water-soluble organic nitrogen (WSON), aerosol samples were collected over the subarctic western North Pacific Ocean in the summer of 2016 aboard the Korean icebreaker IBR/V Araon. During the cruise, concentrations of NH4+, NO3−, and WSON in bulk (fine + coarse) aerosols ranged from 0.768 to 25.3, 0.199 to 5.94, and 0.116 to 14.7 nmol m−3, respectively. Contributions of NH4+, NO3−, and WSON to total water-soluble N represented ~74%, ~17%, and ~9%, respectively. Water-soluble N concentrations showed a strong gradient from the East Asian continent to the subarctic western North Pacific Ocean, indicating that water-soluble N species were mainly derived from anthropogenic or terrestrial sources. During sea fog events, coarse mode NO3− was likely to be scavenged more efficiently by fog droplets than fine mode NO3−; besides, WSON was detected only in fine mode, suggesting that there may have been a significant influence of sea fog on WSON, such as the photochemical conversion of WSON into inorganic N. Mean dry deposition flux for water-soluble total N (6.3 ± 9.4 µmol m−2 d−1) over the subarctic western North Pacific Ocean was estimated to support a minimum carbon uptake of 42 ± 62 µmol C m−2d−1 by using the Redfield C/N ratio of 6.625.

Influence of peat fires on the rainwater chemistry in intra-mountain basins with specific atmospheric circulations (Eastern Carpathians, Romania)

A comprehensive study on the chemical composition of precipitation, the influence of peat fires and their relations with atmospheric circulation was conducted in the year of 2012, in two intra-mountain basins, the Ciuc basin (CB) and the Giurgeu basin (GB), Eastern Carpathians, Romania. Atmospheric circulation types showed the presence of a westerly anticyclonic circulation, characterized by a strong development of the Azores High to the northern Atlantic, contributing to the appearance of peat-fires. Using ROCADA daily gridded climatic datasets, the maximum and minimum daily temperatures were extracted, showing deviation from 2 °C to 6 °C in the studied year against the multiannual mean for the 1981-2016 period. Rainwater samples were analyzed for pH, major anions and cations; HCO₃^- concentrations were calculated based on the empirical relationship between pH and HCO₃^-. The results showed that 45.16% and 54.55% of precipitation had pH > 7.0 at CB and GB, respectively. NH₃, NH₄⁺ and Ca²⁺ are the main neutralizing agents. The significant correlation between SO₄^2- and NH₄⁺ (r = 0.711 - CB; r = 0.736 - GB) indicated neutralization by NH₃ in the forms of (NH4)₂SO₄ and NH₄HSO₄. Positive regression coefficient between the sum of (H⁺ + [NH₄⁺] + [Ca²⁺]) and the sum of ([nss - SO₄^2-] + [NO₃^-]) (r = 0.855 - CB; r = 0.796 - GB), showed that acid neutralization was primarily brought by NH₄⁺ and/or CaCO₃. Using Na as an indicator of marine origin, the proportions of sea salt and non-sea-salt were estimated from elemental ratios. According to correlation analysis and PCA, main acidic ions (SO₄^2- and NO₃^-) and NH₄⁺ were mainly derived from anthropogenic activities (biomass burning, peat fires, fertilization), while Ca²⁺ and Mg²⁺ originated from terrestrial sources. The behavior of gaseous pollutants and smoke distribution resulted from peat fires were deciphered using the HYSPLIT model in a case study.

The indoor-outdoor characteristics of water-soluble ion in PM2.5 in Tianjin wintertime

The indoor and outdoor PM_2.5 mass concentration, water-soluble ion by filter sampler was analyzed on December 3-21, 2015 during wintertime in Tianjin, China. The results indicate that high humidity conditions result in the accumulation of atmospheric pollutants and reduce atmosphere visibility. The I/O ratio for PM_2.5 concentration in dormitory and lab are less than 1 in haze days. Indoor PM_2.5 concentration increases rapidly with outdoor PM_2.5 concentration increasing in haze days. The filtration factors of the dormitory and lab indicate nearly half of the outdoor PM_2.5 enters indoor environment. The human activities in dormitory could cause more the formation of PM_2.5 than those in lab. The concentration of SO₄^2- is the highest ion in water-soluble ion for outdoor PM_2.5. The SO₄^2-, NO₃^-, NH₄⁺, and Cl^- are generated mainly by outdoor sources; however, the Na⁺, Ca²⁺, and Mg²⁺ are generated mainly by indoor sources. The NH₄NO₃, (NH₄)₂SO₄, and NH₄Cl accounts for 20.2~41.8%, 32.0~51.4%, and 6.4~10.6% of the total water-soluble ion in different indoor-outdoor environment. The total secondary aerosols including NH₄NO₃, (NH₄)₂SO₄, and NH₄Cl in PM_2.5 are 28.3, 42.1, 28.2, 31.0, and 33.9% in outdoor environment for haze days, outdoor environment for non-haze days, dormitory for haze days, dormitory for non-haze days, and lab for haze days, respectively.

A molecular perspective for global modeling of upper atmospheric NH3 from freezing clouds

Ammonia plays a key role in the neutralization of atmospheric acids such as sulfate and nitrates. A few in situ observations have supported the theory that gas-phase NH₃ concentrations should decrease sharply with altitude and be extremely low in the upper troposphere and lower stratosphere (UTLS). This theory, however, seems inconsistent with recent satellite measurements and is also not supported by the aircraft data showing highly or fully neutralized sulfate aerosol particles by ammonium in the UTLS in many parts of the world. Here we reveal the contributions of deep convective clouds to NH₃ in the UTLS by using integrated cross-scale modeling, which includes molecular dynamic simulations, a global chemistry transport model, and satellite and aircraft measurements. We show that the NH₃ dissolved in liquid cloud droplets is prone to being released into the UTLS upon freezing during deep convection. Because NH₃ emission is not regulated in most countries and its future increase is likely persistent from agricultural growth and the warmer climate, the effect of NH₃ on composition and phase of aerosol particles in the UTLS can be significant, which in turn can affect cirrus cloud formation, radiation, and the budgets of NOx and O₃.

Characterization and Local Emission Sources for Ammonia in an Urban Environment

Ammonia levels were evaluated in the urban environment of Madrid City, Spain. A total of 110 samplers were distributed throughout the city. Vehicle traffic density, garbage containers and sewers were identified as local emission sources of ammonia. The average ammonia concentrations were 4.66 ± 2.14 µg/m³ (0.39-11.23 µg/m³ range) in the winter and 5.30 ± 1.81 µg/m³ (2.33-11.08 µg/m³ range) in the summer. Spatial and seasonal variations of ammonia levels were evaluated. Hotspots were located in the south and center of Madrid City in both winter and summer seasons, with lower ammonia concentrations located in the north (winter) and in the west and east (summer). The number of representative points that were needed to establish a reliable air quality monitoring network for ammonia was determined using a combined clustering and kriging approach. The results indicated that 40 samplers were sufficient to provide a reliable estimate for Madrid City.

Role of ammonium ion and transition metals in the formation of secondary organic aerosol and metallo-organic complex within fog processed ambient deliquescent submicron particles collected in central part of Indo-Gangetic Plain

In this study we observed the role of ammonium ion (NH₄⁺) and transition metals (Fe, Mn, Cr, and Cu) present in ambient submicron particles in stabilizing and enhancing the yield of water soluble organic carbon (WSOC). A good correlation of WSOC with transition metals and NH₄⁺ was found (R² = 0.87 and 0.71), respectively within foggy episode collected ambient PM₁ (particles having aerodynamic diameter ≤1.0 μm) suggesting plausibleness of alternate oxidation (primarily various carbonyls into their respective organic acids, esters and other derivatives.) and aging mechanisms. Molar concentration of ammonium ion was observed to be exceeded over and above to require in neutralizing the sulphate and nitrate which further hints its role in the neutralization, stabilization and enhancement of subset of WSOC such as water soluble organic acids. Transition metals were further apportioned using enrichment factor analysis. The source of Fe, Mn, and Cr was found to be crustal and Cu was tagged to anthropogenic origin. This study also described the plausible role of significant predictors (Fe and Cu) in the secondary organic aerosol (SOA) formation through effect of Fenton chemistry. Mass-to-charge ratio of identified oxalic acid from our published recent field study (carried out from same sampling location) was used for understanding the possible metallo-organic complex with Fe supports the substantial role of Fe in SOA formation in the deliquescent submicron particles facilitated by aqueous-phase chemistry.

Improving organic aerosol treatments in CESM/CAM5: Development, application, and evaluation

New treatments for organic aerosol (OA) formation have been added to a modified version of the CESM/CAM5 model (CESM-NCSU). These treatments include a volatility basis set treatment for the simulation of primary and secondary organic aerosols (SOAs), a simplified treatment for organic aerosol (OA) formation from glyoxal, and a parameterization representing the impact of new particle formation (NPF) of organic gases and sulfuric acid. With the inclusion of these new treatments, the concentration of oxygenated organic aerosol increases by 0.33 µg m-3 and that of primary organic aerosol (POA) decreases by 0.22 µg m-3 on global average. The decrease in POA leads to a reduction in the OA direct effect, while the increased OOA increases the OA indirect effects. Simulations with the new OA treatments show considerable improvement in simulated SOA, oxygenated organic aerosol (OOA), organic carbon (OC), total carbon (TC), and total organic aerosol (TOA), but degradation in the performance of HOA. In simulations of the current climate period, despite some deviations from observations, CESM-NCSU with the new OA treatments significantly improves the magnitude, spatial pattern, seasonal pattern of OC and TC, as well as, the speciation of TOA between POA and OOA. Sensitivity analysis reveals that the inclusion of the organic NPF treatment impacts the OA indirect effects by enhancing cloud properties. The simulated OA level and its impact on the climate system are most sensitive to choices in the enthalpy of vaporization and wet deposition of SVOCs, indicating that accurate representations of these parameters are critical for accurate OA-climate simulations.

Assessing the Future Vehicle Fleet Electrification: The Impacts on Regional and Urban Air Quality

There have been significant advancements in electric vehicles (EVs) in recent years. However, the different changing patterns in emissions at upstream and on-road stages and complex atmospheric chemistry of pollutants lead to uncertainty in the air quality benefits from fleet electrification. This study considers the Yangtze River Delta (YRD) region in China to investigate whether EVs can improve future air quality. The Community Multiscale Air Quality model enhanced by the two-dimensional volatility basis set module is applied to simulate the temporally, spatially, and chemically resolved changes in PM_2.5 concentrations and the changes of other pollutants from fleet electrification. A probable scenario (Scenario EV1) with 20% of private light-duty passenger vehicles and 80% of commercial passenger vehicles (e.g., taxis and buses) electrified can reduce average PM_2.5 concentrations by 0.4 to 1.1 μg m^-3 during four representative months for all urban areas of YRD in 2030. The seasonal distinctions of the air quality impacts with respect to concentration reductions in key aerosol components are also identified. For example, the PM_2.5 reduction in January is mainly attributed to the nitrate reduction, whereas the secondary organic aerosol reduction is another essential contributor in August. EVs can also effectively assist in mitigating NO₂ concentrations, which would gain greater reductions for traffic-dense urban areas (e.g., Shanghai). This paper reveals that the fleet electrification in the YRD region could generally play a positive role in improving regional and urban air quality.

Diurnal Variability in Chlorophyll-a, Carotenoids, CDOM and SO₄(2-) Intensity of Offshore Seawater Detected by an Underwater Fluorescence-Raman Spectral System

A newly developed integrated fluorescence-Raman spectral system (λ_ex = 532 nm) for detecting Chlorophyll-a (chl-a), Chromophoric Dissolved Organic Matter (CDOM), carotenoids and SO₄²⁻ in situ was used to successfully investigate the diurnal variability of all above. Simultaneously using the integration of fluorescence spectroscopy and Raman spectroscopy techniques provided comprehensive marine information due to the complementarity between the different excitation mechanisms and different selection rules. The investigation took place in offshore seawater of the Yellow Sea (36°05′40′′ N, 120°31′32′′ E) in October 2014. To detect chl-a, CDOM, carotenoids and SO₄²⁻, the fluorescence-Raman spectral system was deployed. It was found that troughs of chl-a and CDOM fluorescence signal intensity were observed during high tides, while the signal intensity showed high values with larger fluctuations during ebb-tide. Chl-a and carotenoids were influenced by solar radiation within a day cycle by different detection techniques, as well as displaying similar and synchronous tendency. CDOM fluorescence cause interference to the measurement of SO₄²⁻. To avoid such interference, the backup Raman spectroscopy system with λ_ex = 785 nm was employed to detect SO₄²⁻ concentration on the following day. The results demonstrated that the fluorescence-Raman spectral system has great potential in detection of chl-a, carotenoids, CDOM and SO₄²⁻ in the ocean.

Eight-year (2007-2014) trends in ambient fine particulate matter (PM2.5) and its chemical components in the Capital Region of Alberta, Canada

Currently there have been questions about ambient fine particulate matter (PM2.5) levels in the Capital Region of Alberta, Canada. An investigation of temporal trends in PM2.5 and its chemical components was undertaken in the City of Edmonton within the Capital Region over an 8-year period (2007-2014). A non-parametric trend detection method was adopted to characterize trends in ambient concentrations. No statistically significant change was observed for ambient PM2.5 concentrations during 2007-2014, while significant decreasing trends were found for organic carbon, elemental carbon, oxalate, barium, lead and cadmium. A statistically significant increasing trend was observed for sodium chloride indicating an increase of de-icing salt contribution for winter road maintenance in recent years. Concentrations of potassium ion and zinc exhibited strong and significant seasonal variability with higher concentrations in winter than in summer likely reflecting wood smoke origins more than other potential sources in Edmonton and the surrounding region. No statistically significant changes were observed for all other chemical components examined. Notwithstanding robust population growth that has occurred in Edmonton, these findings reveal that particulate air quality and corresponding trace elements in Edmonton's air has been unchanged or improved over the investigated period (2007-2014). Longer-term air quality monitoring at least over several decades is needed to establish whether trends reported here are actually occurring.

Oxygen and nitrogen isotopic composition of nitrate in commercial fertilizers, nitric acid, and reagent salts

Nitrate is a key component of synthetic fertilizers that can be beneficial to crop production in agro-ecosystems, but can also cause damage to natural ecosystems if it is exported in large amounts. Stable isotopes, both oxygen and nitrogen, have been used to trace the sources and fate of nitrate in various ecosystems. However, the oxygen isotope composition of synthetic and organic nitrates is poorly constrained. Here, we present a study on the N and O isotope composition of nitrate-based fertilizers. The δ(15)N values of synthetic and natural nitrates were 0 ± 2 ‰ similar to the air N2 from which they are derived. The δ(18)O values of synthetic nitrates were 23 ± 3 ‰, similar to air O2, and natural nitrate fertilizer δ(18)O values (55 ± 5 ‰) were similar to those observed in atmospheric nitrate. The Δ(17)O values of synthetic fertilizer nitrate were approximately zero following a mass-dependent isotope relationship, while natural nitrate fertilizers had Δ(17)O values of 18 ± 2 ‰ similar to nitrate produced photochemically in the atmosphere. These narrow ranges of values can be used to assess the amount of nitrate arising from fertilizers in mixed systems where more than one nitrate source exists (soil, rivers, and lakes) using simple isotope mixing models.

Sources and elemental composition of summer aerosols in the Larsemann Hills (Antarctica)

Atmospheric aerosols play a major role in the global climate change. A better physical characterization of the chemical composition of atmospheric aerosols, especially in remote atmosphere, is an important step to reduce the current uncertainty in their effect on the radiative forcing of the climate. In the present work, surface aerosols have been studied over the Southern Ocean and over Bharati, Indian Research Station at Larsemann Hills at the Antarctic coast during the summer season of 2009-2010. Aerosol samples were collected using optical particle counter (OPC) and high-volume air sampler. PM10 and PM2.5 aerosol samples were analyzed for various water-soluble and acid-soluble ionic constituents. The Hysplit model was used to compute the history of the air masses for their possible origin. Supplementary measurements of meteorological parameters were also used. The average mass concentration for PM10 over the Southern Ocean was found to be 13.4 μg m(3). Over coastal Antarctica, the mass of PM10 was 5.13 μg m(-3), whereas that of PM2.5 was 4.3 μg m(-3). Contribution of marine components, i.e., Na, Cl and Mg was dominant over the Southern Ocean (79 %) than over the coastal Antarctica where they were dominant in coarse mode (67 %) than in fine mode (53 %) aerosols. The NH4/nss-SO4 ratio of 1.12 in PM2.5 indicates that the NH4 and SO4 ions were in the form of NH4HSO4. Computation of enrichment factors indicate that elements of anthropogenic origin, e.g., Zn, Cu, Pb, etc., were highly enriched with respect to crustal composition.

Changes in atmospheric nitrate deposition in Germany--an isotopic perspective

We investigated the isotopic composition of atmospheric NO3(-) deposition at a moderately polluted site in Western Europe over an annual cycle from December 2011 to November 2012. On average, we measured load-weighted δ(15)N values of +0.1 and +3.0‰ in wet and dry deposition, respectively. A comparison to source-specific N emission trends and to isotope data from the 1980s reveals distinct changes in δ(15)N-NO3(-) values: In contrast to the increasing relative importance of isotopically depleted natural NOx sources, we find an increase of isotope values in comparison to historical data. We explore the role of land-based N sources, because backward trajectories reveal a correlation of higher δ(15)N to air mass origin from industrialized areas. Nowadays isotopically enriched NOx of coal-fired power plants using selective catalytic converters and land-based vehicle emissions, which use same technology, are apparently the main driver of rising δ(15)N values in nitrate deposition.

A study of diurnal variations of PM2.5 acidity and related chemical species using a new thermodynamic equilibrium model

Aerosol acidity is one of the most important parameters that can influence atmospheric visibility, climate change and human health. Based on continuous field measurements of inorganic aerosol species and their thermodynamic modeling on a time resolution of 1h, this study has investigated the acidic properties of PM2.5 and their relation with the formation of secondary inorganic aerosols (SIA). The study was conducted by taking into account the prevailing ambient temperature (T) and relative humidity (RH) in a tropical urban atmosphere. The in-situ aerosol pH (pH(IS)) on a 12h basis ranged from -0.20 to 1.46 during daytime with an average value of 0.48 and 0.23 to 1.53 during nighttime with an average value of 0.72. These diurnal variations suggest that the daytime aerosol was more acidic than that caused by the nighttime aerosol. The hourly values of pH(IS) showed a reverse trend as compared to that of in-situ aerosol acidity ([H(+)]Ins). The pH(IS) had its maximum values at 3:00 and at 20:00 and its minimum during 11:00 to 12:00. Correlation analyses revealed that the molar concentration ratio of ammonium to sulfate (R(N/S)), equivalent concentration ratio of cations to anions (RC/A), T and RH can be used as independent variables for prediction of pH(IS). A multi-linear regression model consisting of RN/S, RC/A, T and RH was developed to estimate aerosol pH(IS).

Sulfur dioxide emissions from combustion in china: from 1990 to 2007

China has become the world's largest emitter of SO(2) since 2005, and aggressive deployment of flue gas desulfurization (FGD) at coal-fired power plants appeared in China when facing the formidable pressure of environment pollution. In this work, we estimate the annual emission from combustion sources at provincial levels in China from 1990 to 2007, with updated data investigations. We have implemented the method of transportation matrix to gain a better understanding of sulfur content of coal in consuming provinces, which in turn improved the inventory. The total emissions from combustion in 2007 were 28.3 Tg, half of which was contributed by coal-fired power plants. Meanwhile, the industrial boiler coal combustion and residential coal consumed in centralized heating were responsible for another 32% of the total emissions. From 1990 to 2007, annual SO(2) emission was fluctuated with two peaks (1996 and 2006), and total emission doubled from 15.4 Tg to 30.8 Tg, at an annual growth rate of 4.4% (6.3% since 2000). Due to the extensive application of FGD technology and the phase-out of small, high emitting units, the SO(2) emission began to decrease after 2006. Furthermore, the differences among estimates reported in literatures highlight a great need for further research to reduce the uncertainties with more detailed information on key sources and actual operation of devices.

Depression of ammonia uptake to sulfuric acid aerosols by competing uptake of ambient organic gases

The neutralization of acidic aerosols by ammonia has been studied through experiments which combine ambient air with laboratory generated sulfuric acid aerosol. Results indicated that acidic aerosol mixed with organic free air and ammonia was neutralized on a time scale<1 min, consistent with expectations. However, in the presence of ambient organic gases and ammonia, the rate of aerosol neutralization is significantly reduced. This reduction in ammonia uptake was concurrent with an increase in the amount of particle phase organics. A steady state in the NH4+/SO4(2-) in the presence of organic gases was established on time scales of 10 min to several hours, corresponding to NH3 uptake coefficients in the range of 4×10(-3)-2×10(-4). The degree to which neutralization was slowed was dependent upon the initial ammonia concentration and the organic mass added to the aerosols. These results suggest that inorganic equilibrium thermodynamic models may overestimate the rate of ammonia uptake and that ambient particles may remain acidic for longer than previously expected.

Uptake and surface reaction of methanol by sulfuric acid solutions investigated by vibrational sum frequency generation and Raman spectroscopies

The uptake of methanol at the air-liquid interface of 0-96.5 wt % sulfuric acid (H2SO4) solutions has been observed directly using vibrational sum frequency generation (VSFG) spectroscopy. As the concentration of H2SO4 increases, the VSFG spectra reveal a surface reaction between methanol and H2SO4 to form methyl hydrogen sulfate. The surface is saturated with the methyl species after 15 min. The uptake of methyl species into the solutions by Raman spectroscopy was also observed and occurred on a much longer time scale. This suggests that uptake of methanol by sulfuric acid solutions is diffusion-limited.