Particulate SO2 Research Articles

Insights into atmospheric trace gases, aerosols, and transport processes at a high-altitude station (2623 m a.s.l.) in Northeast Asia

As part of the efforts to understand long-range air pollution transport in Northeast Asia, a comprehensive field measurement campaign was conducted at the top of Changbai Mountain (2623 m a.s.l.) from 25th July to 21st August in 2021. The ambient concentrations of trace gases and chemical characteristics of fine particulate matter (PM2.5) were comparable to those at background or free tropospheric locations in China, but exceeded levels at corresponding sites in Europe and the United States. Well-defined diurnal variations were evident in most air pollutants, including carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen oxide (NOx), reflecting the influence of boundary layer development and local anthropogenic activities. Ozone (O3) exhibited a unique diurnal distribution, with lower concentrations during the daytime and higher levels at nighttime, indicating a pronounced impact of downward transport of O3-rich air from the upper troposphere during the nighttime. During the campaign, organic carbon (OC) constituted the predominant component of PM2.5, comprising 43% of the total, while sulfate (SO42−) was the most abundant secondary inorganic component in PM2.5, accounting for 26%. Combining the analysis of air mass backward trajectories, we found that Changbai Mountain is primarily influenced by air masses originating from North Korea and the Sea of Japan, constituting 62% of the total, and local vegetation biological emissions and anthropogenic emissions in North Korea notably affect the observation site. Conversely, the secondary aerosol components were most abundant in marine air mass originating from the marginal seas of China and the strait between the Korean peninsula and southern Japan. Utilizing the Lagrangian photochemical trajectory model (LPTM), a significant increase in particulate SO42− concentrations was observed when air mass passed through the marginal seas of China, primarily due to SO2 oxidation reaction. This study contributes to an improved understanding of the atmospheric chemistry in the high-altitude regions of Northeast Asia and underscores the substantial role of secondary inorganic aerosol formation during the transport of marine air masses.

Direct Observation of Sulfate Explosive Growth in Wet Plumes Emitted From Typical Coal‐Fired Stationary Sources

AbstractThe origins of atmospheric sulfate production have previously been explained by focusing on air quality models and complex chemical reaction processes. Here, we first report direct observations of sulfate production in stack plumes discharged from coal‐fired power plants, industrial boilers, and sintering plants equipped with wet desulfurization systems. Less than one third of the particulate SO42− in plumes is attributed to dust‐SO42− and SO3 measured in stacks. The SO2 aqueous‐phase oxidation process is critical in explaining the unknown sulfate formation in plume droplets with pH values ranging from 2.3 to 2.8. When the rapidly formed sulfate in wet plumes is included, a notable amount of underestimated sulfate (∼0.24 Tg in 2017) is emitted from industrial stacks in China and can partially explain the “missing sulfate” on driving most particle pollution episodes. Policy‐making targeting particulate emissions is suggested to substantially reduce sulfate emissions for further air quality improvement.

Pan-European rural monitoring network shows dominance of NH<sub>3</sub> gas and NH<sub>4</sub>NO<sub>3</sub> aerosol in inorganic atmospheric pollution load

Abstract. A comprehensive European dataset on monthly atmospheric NH3, acid gases (HNO3, SO2, HCl), and aerosols (NH4+, NO3-, SO42-, Cl−, Na+, Ca2+, Mg2+) is presented and analysed. Speciated measurements were made with a low-volume denuder and filter pack method (DEnuder for Long-Term Atmospheric sampling, DELTA®) as part of the EU NitroEurope (NEU) integrated project. Altogether, there were 64 sites in 20 countries (2006–2010), coordinated between seven European laboratories. Bulk wet-deposition measurements were carried out at 16 co-located sites (2008–2010). Inter-comparisons of chemical analysis and DELTA® measurements allowed an assessment of comparability between laboratories. The form and concentrations of the different gas and aerosol components measured varied between individual sites and grouped sites according to country, European regions, and four main ecosystem types (crops, grassland, forests, and semi-natural). The smallest concentrations (with the exception of SO42- and Na+) were in northern Europe (Scandinavia), with broad elevations of all components across other regions. SO2 concentrations were highest in central and eastern Europe, with larger SO2 emissions, but particulate SO42- concentrations were more homogeneous between regions. Gas-phase NH3 was the most abundant single measured component at the majority of sites, with the largest variability in concentrations across the network. The largest concentrations of NH3, NH4+, and NO3- were at cropland sites in intensively managed agricultural areas (e.g. Borgo Cioffi in Italy), and the smallest were at remote semi-natural and forest sites (e.g. Lompolojänkkä, Finland), highlighting the potential for NH3 to drive the formation of both NH4+ and NO3- aerosol. In the aerosol phase, NH4+ was highly correlated with both NO3- and SO42-, with a near-1:1 relationship between the equivalent concentrations of NH4+ and sum (NO3-+ SO42-), of which around 60 % was as NH4NO3. Distinct seasonality was also observed in the data, influenced by changes in emissions, chemical interactions, and the influence of meteorology on partitioning between the main inorganic gases and aerosol species. Springtime maxima in NH3 were attributed to the main period of manure spreading, while the peak in summer and trough in winter were linked to the influence of temperature and rainfall on emissions, deposition, and gas–aerosol-phase equilibrium. Seasonality in SO2 was mainly driven by emissions (combustion), with concentrations peaking in winter, except in southern Europe, where the peak occurred in summer. Particulate SO42- showed large peaks in concentrations in summer in southern and eastern Europe, contrasting with much smaller peaks occurring in early spring in other regions. The peaks in particulate SO42- coincided with peaks in NH3 concentrations, attributed to the formation of the stable (NH4)2SO4. HNO3 concentrations were more complex, related to traffic and industrial emissions, photochemistry, and HNO3:NH4NO3 partitioning. While HNO3 concentrations were seen to peak in the summer in eastern and southern Europe (increased photochemistry), the absence of a spring peak in HNO3 in all regions may be explained by the depletion of HNO3 through reaction with surplus NH3 to form the semi-volatile aerosol NH4NO3. Cooler, wetter conditions in early spring favour the formation and persistence of NH4NO3 in the aerosol phase, consistent with the higher springtime concentrations of NH4+ and NO3-. The seasonal profile of NO3- was mirrored by NH4+, illustrating the influence of gas–aerosol partitioning of NH4NO3 in the seasonality of these components. Gas-phase NH3 and aerosol NH4NO3 were the dominant species in the total inorganic gas and aerosol species measured in the NEU network. With the current and projected trends in SO2, NOx, and NH3 emissions, concentrations of NH3 and NH4NO3 can be expected to continue to dominate the inorganic pollution load over the next decades, especially NH3, which is linked to substantial exceedances of ecological thresholds across Europe. The shift from (NH4)2SO4 to an atmosphere more abundant in NH4NO3 is expected to maintain a larger fraction of reactive N in the gas phase by partitioning to NH3 and HNO3 in warm weather, while NH4NO3 continues to contribute to exceedances of air quality limits for PM2.5.

Size Distribution of Atmospheric Particles: 40-Year Trends and 20-Year Comparisons of Chemical Constituents between Residential and Roadside Areas in Osaka City, Japan

Long-term observational data for the size distributions and particulate chemical components have been summarized to understand the past and current particulate conditions in Osaka City. The positive matrix factorization (PMF) method was also applied to estimate the source changes. The observational data obtained using Andersen cascade impactors reveals that for the 40 years from fiscal year (FY) 1976 to 2015, there was a 70% reduction in PMfine (less than 2.1 μm of the aerodynamic diameter) and 76% reduction in PMcoarse (over 2.1 μm). These correspond to a 71% and 74% reduction in PM2.5 (particulate matter less than 2.5 μm in diameter) and PM10-2.5, respectively. From the continuous chemical measurements made in this study, we observed a more than 50% reduction in coarse particulate elemental carbon (EC), SO42−, NH4+, Zn, Pb, and Cd, commonly in residential and roadside areas, over the last 20 years. Similarly, the level of the fine particulate EC, Ca2+, Cl−, Zn, Mg2+, Pb, and Cd was reduced by more than 50%. Notably, the results of the particulate component analysis of ECfine show a typical reduction of 73%–79% for 20 years, and this is the main component contributing to the reduction of atmospheric particulate concentration. However, there seems to have been no apparent reduction of Vfine concentrations, SO42−fine showed a relatively low reduction of 19% to 26%, and NH4+fine levels fell by 14% to 21% in 20 years. Since fine sulfate and ammonium have similar behaviors, ammonium sulfate is considered to be a secondary particle aerosol because of long-range transportation. The PMF analysis still estimates a high contribution rate of secondary particles, which is one of the current problems. In contrast, although vanadium is a minor element, it is likely to be generated from harbor areas with ships because they are susceptible to the prevailing sea breeze in summer. Therefore, in the future, it will be necessary to scrutinize and take countermeasures not only for long-range transportation but also for domestic sources.

Near real-time PM1 chemical composition measurements at a French urban background and coastal site under industrial influence over more than a year: Temporal variability and assessment of sulfur-containing emissions

Near real-time measurements of submicron particulate matter (PM1) were carried out at an industrial and coastal site in Dunkirk (Northern France) over a 14-month period (July 2013–September 2014). This site is surrounded by various industrial plants (metallurgy, petrochemistry, food processing, power plant, etc.) and is characterized by intense ship traffic (~700–800 per day along the English Channel) in harbour surroundings. The non-refractory (NR) submicron particles (organics, sulfate, nitrate, ammonium and chloride) and black carbon were measured by an Aerosol Chemical Speciation Monitor (ACSM) and an Aethalometer, respectively. Concomitant monitoring of CO2, SO2, and meteorological parameters was also performed. Both the seasonal (five seasons including two summers) and spatial (four identified sectors of emissions: marine, urban, industrial-urban and industrial) variabilities were investigated.We present a descriptive analysis of the PM1 composition, whose ambient concentrations ranged from less than 1 μg m−3 up to approximately 100 μg m−3 during a few pollution events. Gaseous SO2 and particulate SO4 were systematically observed at high concentrations (up to 310 and 48.2 μg m−3, respectively) when industrial plumes reached the monitoring site. The conversion ratio of particulate (Sp) to total (Stot) sulfur is relatively constant at 0.1 when RH ranges from 30 to 70% but reaches an average value of 0.3 at high RH (90–100%). This reflects an enhancement of SO2-to-SO4 gas-particle conversion processes resulting in an increase of aerosol acidity as shown by a comparison between measured and predicted NH4 concentrations. An impact of the vertical mixing on the SO2-to-SO4 conversion was also observed using vertical turbulence (σw) as a descriptive parameter. Indeed, the conversion ratio (Sp/Stot) was found to be reduced under high turbulence conditions due to dilution effects.

Strong anthropogenic control of secondary organic aerosol formation from isoprene in Beijing

Abstract. Isoprene-derived secondary organic aerosol (iSOA) is a significant contributor to organic carbon (OC) in some forested regions, such as tropical rainforests and the Southeastern US. However, its contribution to organic aerosol in urban areas that have high levels of anthropogenic pollutants is poorly understood. In this study, we examined the formation of anthropogenically influenced iSOA during summer in Beijing, China. Local isoprene emissions and high levels of anthropogenic pollutants, in particular NOx and particulate SO42-, led to the formation of iSOA under both high- and low-NO oxidation conditions, with significant heterogeneous transformations of isoprene-derived oxidation products to particulate organosulfates (OSs) and nitrooxy-organosulfates (NOSs). Ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry was combined with a rapid automated data processing technique to quantify 31 proposed iSOA tracers in offline PM2.5 filter extracts. The co-elution of the inorganic ions in the extracts caused matrix effects that impacted two authentic standards differently. The average concentration of iSOA OSs and NOSs was 82.5 ng m−3, which was around 3 times higher than the observed concentrations of their oxygenated precursors (2-methyltetrols and 2-methylglyceric acid). OS formation was dependant on both photochemistry and the sulfate available for reactive uptake, as shown by a strong correlation with the product of ozone (O3) and particulate sulfate (SO42-). A greater proportion of high-NO OS products were observed in Beijing compared with previous studies in less polluted environments. The iSOA-derived OSs and NOSs represented 0.62 % of the oxidized organic aerosol measured by aerosol mass spectrometry on average, but this increased to ∼3 % on certain days. These results indicate for the first time that iSOA formation in urban Beijing is strongly controlled by anthropogenic emissions and results in extensive conversion to OS products from heterogenous reactions.

Effects of NH3 and alkaline metals on the formation of particulate sulfate and nitrate in wintertime Beijing

Sulfate and nitrate from secondary reactions remain as the most abundant inorganic species in atmospheric particle matter (PM). Their formation is initiated by oxidation (either in gas phase or particle phase), followed by neutralization reaction primarily by NH3, or by other alkaline species such as alkaline metal ions if available. The different roles of NH3 and metal ions in neutralizing H2SO4 or HNO3, however, are seldom investigated. Here we conducted semi-continuous measurements of SO42−, NO3−, NH4+, and their gaseous precursors, as well as alkaline metal ions (Na+, K+, Ca2+, and Mg2+) in wintertime Beijing. Analysis of aerosol acidity (estimated from a thermodynamic model) indicated that preferable sulfate formation was related to low pH conditions, while high pH conditions promote nitrate formation. Data in different mass fraction ranges of alkaline metal ions showed that in some ranges the role of NH3 was replaced by alkaline metal ions in the neutralization reaction of H2SO4 and HNO3 to form particulate SO42− and NO3−. The relationships between mass fractions of SO42− and NO3− in those ranges of different alkaline metal ion content also suggested that alkaline metal ions participate in the competing neutralization reaction of sulfate and nitrate. The implication of the current study is that in some regions the chemistry to incorporate sulfur and nitrogen into particle phase might be largely affected by desert/fugitive dust and sea salt, besides NH3. This implication is particularly relevant in coastal China and those areas with strong influence of dust storm in the North China Plain (NCP), both of which host a number of megacities with deteriorating air quality.

Global sensitivity and uncertainty analysis of an atmospheric chemistry transport model: the FRAME model (version 9.15.0) as a case study

Abstract. Atmospheric chemistry transport models (ACTMs) are widely used to underpin policy decisions associated with the impact of potential changes in emissions on future pollutant concentrations and deposition. It is therefore essential to have a quantitative understanding of the uncertainty in model output arising from uncertainties in the input pollutant emissions. ACTMs incorporate complex and non-linear descriptions of chemical and physical processes which means that interactions and non-linearities in input–output relationships may not be revealed through the local one-at-a-time sensitivity analysis typically used. The aim of this work is to demonstrate a global sensitivity and uncertainty analysis approach for an ACTM, using as an example the FRAME model, which is extensively employed in the UK to generate source–receptor matrices for the UK Integrated Assessment Model and to estimate critical load exceedances. An optimised Latin hypercube sampling design was used to construct model runs within ±40 % variation range for the UK emissions of SO2, NOx, and NH3, from which regression coefficients for each input–output combination and each model grid ( > 10 000 across the UK) were calculated. Surface concentrations of SO2, NOx, and NH3 (and of deposition of S and N) were found to be predominantly sensitive to the emissions of the respective pollutant, while sensitivities of secondary species such as HNO3 and particulate SO42−, NO3−, and NH4+ to pollutant emissions were more complex and geographically variable. The uncertainties in model output variables were propagated from the uncertainty ranges reported by the UK National Atmospheric Emissions Inventory for the emissions of SO2, NOx, and NH3 (±4, ±10, and ±20 % respectively). The uncertainties in the surface concentrations of NH3 and NOx and the depositions of NHx and NOy were dominated by the uncertainties in emissions of NH3, and NOx respectively, whilst concentrations of SO2 and deposition of SOy were affected by the uncertainties in both SO2 and NH3 emissions. Likewise, the relative uncertainties in the modelled surface concentrations of each of the secondary pollutant variables (NH4+, NO3−, SO42−, and HNO3) were due to uncertainties in at least two input variables. In all cases the spatial distribution of relative uncertainty was found to be geographically heterogeneous. The global methods used here can be applied to conduct sensitivity and uncertainty analyses of other ACTMs.

Development, characterization and first deployment of an improved online reactive oxygen species analyzer

Abstract. Inhalation of atmospheric particles is linked to human diseases. Reactive oxygen species (ROS) present in these atmospheric aerosols may play an important role. However, the ROS content in aerosols and their formation pathways are still largely unknown. Here, we have developed an online and offline ROS analyzer using a 2′,7′-dichlorofluorescin (DCFH) based assay. The ROS analyzer was calibrated with H2O2 and its sensitivity was characterized using a suite of model organic compounds. The instrument detection limit determined as 3 times the noise is 1.3 nmol L−1 for offline analysis and 2 nmol m−3 of sampled air when the instrument is operated online at a fluorescence response time of approximately 8 min, while the offline method detection limit is 18 nmol L−1. Potential interferences from gas-phase O3 and NO2 as well as matrix effects of particulate SO42− and NO3− were tested, but not observed. Fe3+ had no influence on the ROS signal, while soluble Fe2+ reduced it if present at high concentrations in the extracts. Both online and offline methods were applied to identify the ROS content of different aerosol types, i.e., ambient aerosols as well as fresh and aged aerosols from wood combustion emissions. The stability of the ROS was assessed by comparing the ROS concentration measured by the same instrumentation online in situ with offline measurements. We also analyzed the evolution of ROS in specific samples by conducting the analysis after storage times of up to 4 months. The ROS were observed to decay with increasing storage duration. From their decay behavior, ROS in secondary organic aerosol (SOA) can be separated into short- and long-lived fractions. The half-life of the short-lived fraction was 1.7 ± 0.4 h, while the half-life of the long-lived fraction could not be determined with our uncertainties. All these measurements showed consistently that on average 60 ± 20 % of the ROS were very reactive and disappeared during the filter storage time. This demonstrates the importance of a fast online measurement of ROS.

Radiative and heterogeneous chemical effects of aerosols on ozone and inorganic aerosols over East Asia

Currently, many challenges are faced in simulating ozone(O3), sulfate(SO42−), and nitrate(NO3−) concentrations over East Asia, particularly the overestimation of surface O3 and NO3− concentrations and underestimation of the SO42− concentration during haze episodes. In this study, we examined the radiative and heterogeneous chemical effects of aerosols by incorporating recently reported mechanisms, including self-amplifying SO42− formation, dinitrogen pentoxide (N2O5) hydrolysis, and a heterogeneous reaction converting gaseous nitric acid (HNO3) to nitric oxide (NOx), into a Nested Air Quality Prediction Modeling System. Uptakes by aerosols can be computed through a simple parameterization that is dependent on the aerosol core and shell species, shell thickness, and amount of aerosol liquid water. In this study, a 1-year simulation was conducted for 2013. The updated model successfully reproduced the seasonal and daily observations of O3, fine particulate matter, SO42−, and NO3− concentrations in East Asia. Our results revealed that heterogeneous reactions reduced more surface O3 concentrations (10–20 ppbv) in the polluted regions of East China than did perturbations in photolysis frequencies from aerosols, effectively again improving the comparison between simulations and observations. Oxidation of SO2 by NO2 on wet aerosols significantly enhanced SO42− formation, with sulfate covering approximately ~30–60% of total sulfate concentrations in North China Plain during haze days in winter. The uptake of reactive nitrogen species on aerosols effectively reduced NO3− concentrations and successfully balanced the NOx/HNO3 chemistry in the models. We recommended that larger reductions of gaseous precursors should be considered in China to achieve the national air quality objective. The results show that surface O3 concentrations over East China will increase if the emission of aerosols is reduced without corresponding reductions in O3 precursors.

Effects of submicron ammonium sulfate particles on the growth and yield of komatsuna (Brassica rapa L. var. perviridis)

The aim of this study was to determine the effects of submicron ammonium sulfate (AS) particles on komatsuna (Brassica rapa L. cv. Hakkei) plants. First, we optimized a leaf-washing method to measure the amount of AS particles deposited on the leaf surface of the plants. Then, we used this method to determine the retention time of particles deposited on the leaf surface of the plants. We also investigated the effects of AS particles on the growth and yield of the plants. Almost all the AS particles deposited on the leaf surface were removed within 1 min washing time with ultrapure water, and ion leaching from the leaf was relatively slow but continuous during the leaf-washing procedure. On the basis of these results, we determined that 1 min was a suitable washing time to remove most of the AS particles while minimizing the influence of ion leaching from the leaf. The amount of particulate SO42− deposited on the leaf surface decreased over time, probably because AS particles deposited on the leaf surface deliquesced, allowing ions such as SO42− in the deliquescence solution to be absorbed into the leaf. The plants were grown and exposed to AS particles for 16 days in naturally lit phytotrons. The daily mean increase in the concentration of SO42− in PM2.5 by the exposure to AS particles was 22.5 μg m−3 in the phytotrons. The growth and yield of the plants were significantly reduced by the exposure to AS particles. The exposure to AS particles did not affect the leaf concentrations of nitrogen and chlorophyll, but significantly reduced stomatal conductance. Therefore, stomatal closure is one of the reasons for the AS particle-induced reductions in the growth and yield of komatsuna plants.

Long-term air concentrations, wet deposition, and scavenging ratios of inorganic ions, HNO<sub>3</sub>, and SO<sub>2</sub> and assessment of aerosol and precipitation acidity at Canadian rural locations

Abstract. This study analyzed long-term air concentrations and annual wet deposition of inorganic ions and aerosol and precipitation acidity at 31 Canadian sites from 1983 to 2011. Scavenging ratios of inorganic ions and relative contributions of particulate- and gas-phase species to NH4+, NO3−, and SO42− wet deposition were determined. Geographical patterns of atmospheric Ca2+, Na+, Cl−, NH4+, NO3−, and SO42− were similar to wet deposition and attributed to anthropogenic sources, sea-salt emissions, and agricultural emissions. Decreasing trends in atmospheric NH4+ (1994–2010) and SO42− (1983–2010) were prevalent. Atmospheric NO3− increased prior to 2001 and then declined afterwards. These results are consistent with SO2, NOx and NH3 emission trends in Canada and the USA. Widespread declines in annual NO3− and SO42− wet deposition ranged from 0.07 to 1.0 kg ha−1 a−1 (1984–2011). Acidic aerosols and precipitation impacted southern and eastern Canada more than western Canada; however, both trends have been decreasing since 1994. Scavenging ratios of particulate NH4+, SO42− and NO3− differed from literature values by 22 %, 44 %, and a factor of 6, respectively, because of the exclusion of gas scavenging in previous studies. Average gas and particle scavenging contributions to total wet deposition were estimated to be 72 % for HNO3 and 28 % for particulate NO3−, 37 % for SO2 and 63 % for particulate SO42−, and 30 % for NH3 and 70 % for particulate NH4+.

Concurrent measurements of size-segregated particulate sulfate, nitrate and ammonium using quartz fiber filters, glass fiber filters and cellulose membranes

Current science and policy requirements have focused attention on the need to expand and improve particulate matter (PM) sampling methods. To explore how sampling filter type affects artifacts in PM composition measurements, size-resolved particulate SO42−, NO3− and NH4+ (SNA) were measured on quartz fiber filters (QFF), glass fiber filters (GFF) and cellulose membranes (CM) concurrently in an urban area of Beijing on both clean and hazy days. The results showed that SNA concentrations in most of the size fractions exhibited the following patterns on different filters: CM > QFF > GFF for NH4+; GFF > QFF > CM for SO42−; and GFF > CM > QFF for NO3−. The different patterns in coarse particles were mainly affected by filter acidity, and that in fine particles were mainly affected by hygroscopicity of the filters (especially in size fraction of 0.65–2.1 μm). Filter acidity and hygroscopicity also shifted the peaks of the annual mean size distributions of SNA on QFF from 0.43–0.65 μm on clean days to 0.65–1.1 μm on hazy days. However, this size shift was not as distinct for samples measured with CM and GFF. In addition, relative humidity (RH) and pollution levels are important factors that can enhance particulate size mode shifts of SNA on clean and hazy days. Consequently, the annual mean size distributions of SNA had maxima at 0.65–1.1 μm for QFF samples and 0.43–0.65 μm for GFF and CM samples. Compared with NH4+ and SO42−, NO3− is more sensitive to RH and pollution levels, accordingly, the annual mean size distribution of NO3− exhibited peak at 0.65–1.1 μm for CM samples instead of 0.43–0.65 μm. These methodological uncertainties should be considered when quantifying the concentrations and size distributions of SNA under different RH and haze conditions.

Inorganic ions in ambient fine particles over a National Park in central India: Seasonality, dependencies between SO42−, NO3−, and NH4+, and neutralization of aerosol acidity

Twelve hour integrated ambient fine particles (PM2.5) were collected over an Van Vihar National Park (VVNP), in Bhopal, Central India. Samples were collected on filter substrates every-other-day for two years (2012 and 2013). In addition to PM2.5 mass concentration, water soluble inorganic ions (WSIIs) were also measured. Further, on-site meteorological parameters including temperature, wind speed, wind direction, relative humidity, rainfall and atmospheric pressure were recorded. During 2012, the average PM2.5 concentration was 40 ± 31 μgm−3 while during 2013 it was 48 ± 50 μgm−3. Further, in about 20% of the samples the 12 h integrated fine PM mass exceeded the daily (24 h) average standards (60 μgm−3). This observation suggests that the PM2.5 mass concentration at the study site is likely to be in violation of the National Ambient Air Quality Standard (NAAQS), India. During the study period the sum of three major ions (SO42−, NO3−, and NH4+) accounted for 19.4% of PM2.5 mass on average. Air parcel back trajectory ensembles revealed that emissions from thermal power plants were likely to be the main regional source of particulate SO42− and NO3− measured over VVNP. Further, local traffic activities appeared to have no significant impact on the concentrations of PM2.5 and its WSIIs constituents, as revealed by a day-of-the-week analysis. PM2.5 mass, SO42−, NO3−, and NH4+ showed a pronounced seasonal trend with winter (Jan, Feb) and post-monsoon (Oct, Nov, Dec) highs and pre-monsoon (Mar, Apr, May) and monsoon (Jun, Jul, Aug, Sep) lows, during both 2012 and 2013. Further, when the sum of SO42− and NO3− constituted greater than 90% of water soluble inorganic anions by mass, they were linearly dependent on one another and moderately anti-correlated (r2 = 0.60). The molar ratios of NH4+ and non-sea salt SO42− were examined to understand the aerosol neutralization mechanisms and particulate NO3− formation. An assessment of these ratios and subsequent analyses suggested that in NH4+ rich samples, NO3− and non-sea salt SO42− were almost entirely neutralized by NH4+. In NH4+ poor samples, in addition to NH4+ non-sea salt K+ played a role in acidity neutralization. These observations are unlike those reported for PM10 and total suspended particles (TSP) over other locations in India, where mineral aerosol species (specifically Ca2+) played an important role in neutralizing acidic species. Additionally, both during 2012 and 2013, the aerosol acidity showed a pronounced seasonality - the aerosol was alkaline or near-neutral during the winter and post-monsoon seasons, while during the pre-monsoon and monsoon seasons it was acidic.

Spatial and seasonal variations of atmospheric sulfur concentrations and dry deposition at 16 rural and suburban sites in China

The large emissions of sulfur dioxide (SO2) in China have raised worldwide concerns due to its contribution to acid rain and particulate pollution. Monitoring sulfur (S) concentrations and estimating its deposition are important for evaluating air quality and its effects on ecosystems and human health. To date atmospheric dry S deposition in China remains unclear due to the paucity of measurements, especially in rural regions where the ecosystems are sensitive to acid deposition. In this study, we monitored both SO2 and particulate SO42− (pSO42−) concentrations at 8 sites south and 8 sites north of the Huai River in rural and suburban parts of China between 2010 and 2012. The measured concentration of SO2 and pSO42− were combined with GEOS-Chem modeled dry deposition velocities to estimate dry S deposition inputs to the surfaces. SO2 and pSO42− concentrations were high from October/November to next March/April and they (esp. SO2) decreased sharply since March/April at the northern sites, reflecting elevated SO2 emissions by winter heating (which normally starts in October/November and ends in March/April in the north of the Huai River). However the southern sites did not show this trend. Annual dry deposition of SO2 plus pSO42− in this study ranged from 3.1 to 27.1 kg S ha−1 across all the sites in the year 2011 (except one site from May 2011 to April 2012) and showed large spatial variation. The sites in northern China had greater dry deposition due to the higher S concentrations compared with sites in southern China. We also found relatively low pSO42−/pNO3- ratios at most sites, reflecting NOx emissions had a larger influence than SO2 emissions on particle composition during the 2010–2012 period at the measurement sites. Our results suggest that dry S deposition is still important input to ecosystems in spite of slow reduction of Chinese national SO2 emissions since 2005. More research on both wet and dry S deposition and their impacts on the environment and human health should be carried out following the introduction of policies to reduce SO2 emissions.

Concentration and size distribution of particulate oxalate in marine and coastal atmospheres – Implication for the increased importance of oxalate in nanometer atmospheric particles

In literature, particulate oxalate has been widely studied in the total suspended particles (TSP), particles <10 μm or 2.5 μm (PM10 and PM2.5) and size-segregated particles >100 nm. In this article, we measured oxalate's concentrations in size-segregated atmospheric particles down to 10 nm or 56 nm during eight campaigns performed at a semi-urban coastal site, over the marginal seas of China and from the marginal seas to the northwest Pacific Ocean (NWPO) in 2012–2015. When the sum of the oxalate's concentration in particles <10 μm was used for intercomparison, the lowest average values of 0.05–0.06 μg m−3 were observed during the two campaigns performed at NWPO. The highest average value of 0.38 μg m−3 was observed at the coastal site during a heavy pollution event. Mode analysis results of particulate oxalate and the correlation between oxalate and sulfate suggested that the elevated concentrations of oxalate in PM10 were mainly related to enhanced in-cloud formation of oxalate via anthropogenic precursors. Size distribution data in the total of 136 sets of samples also showed approximately 80% of particulate oxalate's mass existing in atmospheric particles >100 nm. Consistent with previous studies, particulate oxalate in particles >100 nm was a negligible ionic component when comparing to particulate SO42− in the same size range. However, the mole ratios of oxalate/sulfate in particles <100 nm were generally increased by 1–2 orders of magnitude. In approximately 30% of the samples, the mole ratios in atmospheric particles <56 nm were larger than 0.5. Moreover, during Campaign 5, the oxalate's concentrations in <56 nm particles were substantially increased on the days in presence of new particle formation events. These results strongly imply the importance of oxalate in nanometer atmospheric particles, but not in >100 nm atmospheric particles such as PM2.5, PM10, TSP, etc.

Increasing ammonia concentration trends in large regions of the USA derived from the NADP/AMoN network

Data from bi-weekly passive samplers from 18 of the longest operating National Atmospheric Deposition Program’s (NADP) Ammonia Monitoring Network (AMoN) sites (most operating from 2008 to 2015) show that concentrations of NH3 have been increasing (p-value < 0.0001) over large regions of the USA. This trend is occurring at a seasonal and annual level of aggregation. Using random coefficient models (RCM), the mean slope for the 18 sites combined shows an increase of NH3 concentration of +7% per year, with a 95% confidence interval (C.I.) from +5% to +9% per year. Travel blank corrected data using the same approach show increasing NH3 concentrations of +9% (95% C.I. +5% to +13%) per year. During a comparable period (2008–2014) NADP precipitation chemistry sites in the same regions show significant increasing (p-value = 0.0001) precipitation NH4+ concentrations trends for all sites combined of +5% (95% C.I. +3% to +7%) per year.Emissions inventory data for the study period show nearly constant rates of NH3 emissions, but large reductions in NOx and SO2 emissions. Seasonal air quality data from the Clean Air Status and Trends Network (CASTNET) sites in these regions show significant declines in atmospheric particulate SO42− and NH4+, and particulate NO3− plus HNO3 (total NO3−) during the same period. Less formation of acidic SO4 and NO3, due to reduced SO2 and NOx emissions, provide less substrate to interact with NH3 and form particulate ammonium species. Thus, concentrations of NH3 can increase in the atmosphere even if emissions remain constant. A likely result may be more localized deposition of NH3, as opposed to the more long-range transport and deposition of ammonium nitrate (NH4NO3) and sulfate (NH4)2SO4). Additionally, the spatial distribution of wet and dry acidic deposition will be impacted.

Impacts of power generation on air quality in China—part I: An overview

As the fast growth of China’s economy, power generation has greatly increased in past decades. Majority of power generation in China is from coal-fired power plants. Large and still increasing amount of coal combustion for power generation emits numerous pollutants into atmosphere. Combining with emissions from other sources, power generation contributes to the severe air pollution in recent years. In this study, the historic trends and current status of the impact of power generation on air quality in China are overviewed. In 2012, the power sector contributed 30% of CO2, 33% of NOx, 23% of SO2, 8% of particulate matter (PM), 3% of CO, and less than 1% of VOCs emissions in China. The power sector contributed 15% of NOx, 13% of SO2, 27% of O3, 26% of fine particulate NO3− and 22% of fine particulate SO42− ambient concentrations. Coal consumption for power generation is keeping growing. Tremendous efforts have been made to limit emissions from power generation by installing flue-gas desulphurization systems on coal-fired power plant, resulting in reduction of SO2 and PM emissions recently. However, emissions of NOx, CO2, CO, and VOCs are still increasing. Over half of the power emissions and concentrations are distributed in East and North China, which include the Yangtze River Delta and the North China Plain, the two most developed and populous regions in China. Emissions from power generation contribute significant fractions of NOx, SO2, and particulate NO3− in winter, and significant fractions of O3 and particulate SO42− in summer.

Simulating the phase partitioning of NH3, HNO3, and HCl with size-resolved particles over northern Colorado in winter

Numerical modeling of inorganic aerosol processes is useful in air quality management, but comprehensive evaluation of modeled aerosol processes is rarely possible due to the lack of comprehensive datasets. During the Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT) campaign in February and March 2011, the phase partitioning of soluble trace gases with size-resolved particles and related meteorological conditions were measured continuously at a site in Colorado about 33 km north of Denver. These size-resolved measurements of particulate SO42−, NH4+, NO3−, Cl−, Na+, Ca2+, Mg2+, and K+ and inorganic gases are used here to assess the ability of a continental U.S. modeling platform to simulate the gas-particle partitioning of NH3, HNO3, and HCl at this location. Modeling is based on the Community Multiscale Air Quality (CMAQ) model with 12 km horizontal resolution. Baseline, sensitivity, and source apportionment simulations are conducted to fully characterize the model predictions. Considering the limitations in representing regional terrain features in the national 12 km modeling, predictions agree reasonably well with measured concentrations and gas-particle partitioning at this location. However, the median sum of NH4+ and NH3 is underpredicted in the baseline simulation by a factor of four suggesting a need for improved bottom-up NH3 emissions inventories in this area. The median sum of Cl− and HCl is underpredicted by a factor of 2.8, while levels of Ca2+, Mg2+, and K+ are overpredicted. Improvements in windblown and fugitive dust emissions may improve and/or better constrain these predictions. Mass size distributions for inorganic particle constituents are generally simulated well, although the modeled fine particle mode is shifted to slightly larger diameters relative to measurements. Source apportionment modeling estimates of source sector and boundary contributions to air quality at the site are provided.

Ammonia emissions in Europe, part I: Development of a dynamical ammonia emission inventory

Nitrogen input from agricultural ammonia emissions into the environment causes numerous environmental and health problems. The purpose of this study is to present and evaluate an improved ammonia emission inventory based on a dynamical temporal parameterization suitable to compare and assess ammonia abatement strategies. The setup of the dynamical time profile (DTP) consists of individual temporal profiles for ammonia emissions, calculated for each model grid cell, depending on temperature, crop type, fertilizer and manure application, as well as on local legislation. It is based on the method of Skjøth et al., 2004 and Gyldenkærne et al., 2005. The method has been modified to cover the study area and to improve the performance of the emission model. To compare the results of the dynamical approach with the results of the static time profile (STP) the ammonia emission parameterizations have been implemented in the SMOKE for Europe emission model. Furthermore, the influence on secondary aerosol formation in the North Sea region and possible changes triggered through the use of a modified temporal distribution of ammonia emissions were analysed with the CMAQ chemistry transport model. The results were evaluated with observations of the European Monitoring and Evaluation Programme (EMEP). The correlation coefficient of NH3 improved significantly for 12 out of 16 EMEP measurement stations and an improvement in predicting the Normalized Mean Error can be seen for particulate NH4+ and NO3−. The prediction of the 95th percentile of the daily average concentrations has improved for NH3, NH4+ and NO3−. The NH3 concentration modelled with the STP is 157% higher in winter, and about 22% lower in early summer than the one modelled with the new DTP. Consequently, the influence of the DTP on the formation of secondary aerosols is particularly noticeable in winter, when the PM2.5 concentration is 25% lower in comparison to the use of STP for temporal disaggregation. Besides, the formation of particulate SO42− is not influenced by the use of the DTP.