Atmospheric Environment (v.154, #C)

We present results of the vertical distribution variation of volcanic aerosol layers in the upper troposphere and lower stratosphere. The data were taken with our multiwavelength aerosol Raman lidar at Gwangju (35.10° N, 126.53° E), Korea. The volcanic ash particles and gases were released around 12 June 2011 during the eruption of the Nabro volcano (13.37° N, 41.7° E) in Eritrea, east Africa. Forward trajectory computations show that the volcanic aerosols were advected from North Africa to East Asia. The first measurement of the aerosol layer over Korea was on 19 June 2011. The aerosol layers appeared between 15 km and 17 km height asl (above sea level). The maximum value of the aerosol layer of the particle backscatter coefficient (1.5 ± 0.3 Mm−1 sr−1) and the linear particle depolarization ratio at 532 nm (2.2%) were observed at 16.4 km height asl. We continuously probed the upper troposphere and lower stratosphere for this volcanic aerosol layer during the following 6 months, until December 2011. The volcanic aerosol layer showed a single-peak of the particle backscatter coefficient and a comparably narrow vertical thickness at our observation site at the beginning of our observation period (i.e. comparably soon after the initial eruption period). After that initial period the vertical distribution of the plume changed. Multiple peaks and a comparably broad geometrical thickness developed with progressing observation time. The vertical thickness of the volcanic aerosol layer expanded up to 10 km by 3 August 2011. The linear particle depolarization ratios were larger in the lower part of the aerosol layer than the upper part of the aerosol layer. We observed a strong variation of the AOD (aerosol optical depth) in the first two months of our lidar observations. After these two months the AOD gradually decreased with time from September to December 20111 and the maximum particle backscatter coefficients consistently decreased. The corresponding e-folding decay time of the layer AOD was 117 days.
Keywords: Lidar; Volcanic aerosol; Nabro volcano; Depolarization ratio; Stratospheric aerosol;

Optimizing isolation protocol of organic carbon and elemental carbon for 14C analysis using fine particulate samples by Junwen Liu; Jun Li; Ping Ding; Yanlin Zhang; Di Liu; Chengde Shen; Gan Zhang (9-19).
Radiocarbon (14C) analysis is a unique tool that can be used to directly apportion organic carbon (OC) and elemental carbon (EC) into fossil and non-fossil fractions. In this study, a coupled carbon analyzer and high-vacuum setup was established to collect atmospheric OC and EC. We thoroughly investigated the correlations between 14C levels and mass recoveries of OC and EC using urban PM2.5 samples collected from a city in central China and found that: (1) the 14C signal of the OC fraction collected in the helium phase of the EUSSAR_2 protocol (200 °C for 120 s, 300 °C for 150 s, 450 °C for 180 s, and 650 °C for 180 s) was representative of the entire OC fraction, with a relative error of approximately 6%, and (2) after thermal treatments of 120 s at 200 °C, 150 s at 300 °C, and 180 s at 475 °C in an oxidative atmosphere (10% oxygen, 90% helium) and 180 s at 650 °C in helium, the remaining EC fraction sufficiently represented the 14C level of the entire EC, with a relative error of <10%. The average recovery of the OC and EC fractions for 14C analysis was 64± 7% (n = 5) and 87 ± 5% (n = 5), respectively. The fraction of modern carbon in the OC and EC of reference material (RM) 8785 was 0.564 ± 0.013 and 0.238 ± 0.006, respectively. Analysis of 14C levels in four selected PM2.5 samples in Xinxiang, China revealed that the relative contribution of fossil sources in OC and EC in the PM2.5 samples were 50.5± 5.8% and 81.4± 2.6%, respectively, which are comparable to findings in previous studies conducted in other Chinese cities. We confirmed that most urban EC derives from fossil fuel combustion processes, whereas both fossil and non-fossil sources have comparable and important impacts on OC. Our results suggested that water-soluble organic carbon (WSOC) and its pyrolytic carbon can be completely removed before EC collection via the method employed in this study.
Keywords: Radiocarbon; Organic carbon; Elemental carbon; Aerosols; RM 8785;

Modelling trends in ammonia in the Netherlands over the period 1990–2014 by R.J. Wichink Kruit; J. Aben; W. de Vries; F. Sauter; E. van der Swaluw; M.C. van Zanten; W.A.J. van Pul (20-30).
This study investigates to what extent emissions of ammonia, physicochemical processes and meteorology affect the trend in the atmospheric ammonia in the Netherlands between 1993 and 2014. Two distinct periods were distinguished: a period of declining ammonia concentrations between 1993 and 2004 and a period of slightly increasing ammonia concentrations between 2005 and 2014. In the first period, large emission reductions were reported, while the second period is characterized by smaller emission reductions. The Operational Priority Substances (OPS) model was used to quantify the effects of meteorology and physicochemical processes on atmospheric ammonia concentrations. The general performance of the OPS model for ammonia concentration, ammonium concentration and wet deposition of ammonia/ammonium is quite good when evaluated with observations over the whole period. For the period 1993–2004, model sensitivity runs show that the change in atmospheric chemical conditions and specific meteorological conditions can largely explain the smaller decline in ammonia concentrations compared with the decline in ammonia emissions. Uncertainties in emissions such as changes in the timing of manure applications and uncertainties in the estimated excretion and grazing emissions might partly explain remaining differences at the beginning of the period. Low-emission manure spreading techniques have an important reducing effect on the atmospheric ammonia concentration. Without these techniques, the ammonia concentrations at the measurement stations would have been about 3.5–4 μg m−3 higher in recent years. In the period between 2005 and 2014 emissions declined at a much lower rate, but the observed concentrations increased slightly. One third of the observed difference in trends can again be explained by the changed chemical conditions while no explanation has yet been found for the rest.
Keywords: Ammonia; Trends; Modelling; Measurements; Emissions; Codeposition;

A small, lightweight multipollutant sensor system for ground-mobile and aerial emission sampling from open area sources by Xiaochi Zhou; Johanna Aurell; William Mitchell; Dennis Tabor; Brian Gullett (31-41).
Characterizing highly dynamic, transient, and vertically lofted emissions from open area sources poses unique measurement challenges. This study developed and applied a multipollutant sensor and time-integrated sampler system for use on mobile applications such as vehicles, tethered balloons (aerostats) and unmanned aerial vehicles (UAVs) to determine emission factors. The system is particularly applicable to open area sources, such as forest fires, due to its light weight (3.5 kg), compact size (6.75 L), and internal power supply. The sensor system, termed “Kolibri”, consists of sensors measuring CO2 and CO, and samplers for particulate matter (PM) and volatile organic compounds (VOCs). The Kolibri is controlled by a microcontroller which can record and transfer data in real time through a radio module. Selection of the sensors was based on laboratory testing for accuracy, response delay and recovery, cross-sensitivity, and precision. The Kolibri was compared against rack-mounted continuous emissions monitoring system (CEMs) and another mobile sampling instrument (the “Flyer”) that has been used in over ten open area pollutant sampling events. Our results showed that the time series of CO, CO2, and PM2.5 concentrations measured by the Kolibri agreed well with those from the CEMs and the Flyer, with a laboratory-tested percentage error of 4.9%, 3%, and 5.8%, respectively. The VOC emission factors obtained using the Kolibri were consistent with existing literature values that relate concentration to modified combustion efficiency. The potential effect of rotor downwash on particle sampling was investigated in an indoor laboratory and the preliminary results suggested that its influence is minimal. Field application of the Kolibri sampling open detonation plumes indicated that the CO and CO2 sensors responded dynamically and their concentrations co-varied with emission transients. The Kolibri system can be applied to various challenging open area scenarios such as fires, lagoons, flares, and landfills.
Keywords: Sensor system; Emission sampling; Air quality; VOC; PM2.5;

Does temperature nudging overwhelm aerosol radiative effects in regional integrated climate models? by Jian He; Timothy Glotfelty; Khairunnisa Yahya; Kiran Alapaty; Shaocai Yu (42-52).
Nudging (data assimilation) is used in many regional integrated meteorology-air quality models to reduce biases in simulated climatology. However, in such modeling systems, temperature changes due to nudging could compete with temperature changes induced by radiatively active and hygroscopic short-lived tracers leading to two interesting dilemmas: when nudging is continuously applied, what are the relative sizes of these two radiative forces at regional and local scales? How do these two forces present in the free atmosphere differ from those present at the surface? This work studies these two issues by converting temperature changes due to nudging into pseudo radiative effects (PRE) at the surface (PRE_sfc), in troposphere (PRE_atm), and at the top of atmosphere (PRE_toa), and comparing PRE with the reported aerosol radiative effects (ARE). Results show that the domain-averaged PRE_sfc is smaller than ARE_sfc estimated in previous studies and this work, but could be significantly larger than ARE_sfc at local scales. PRE_atm is also much smaller than ARE_atm. These results indicate that appropriate nudging methodology could be applied to the integrated models to study aerosol radiative effects at continental/regional scales, but it should be treated with caution for local scale applications.
Keywords: Nudging; Aerosol radiative effects; Integrated models; Regional climate;

Isotopic ratios of nitrate in aerosol samples from Mt. Lulin, a high-altitude station in Central Taiwan by Tania Guha; C.T. Lin; S.K. Bhattacharya; A.S. Mahajan; Chang-Feng Ou-Yang; Yi-Ping Lan; S.C. Hsu; Mao-Chang Liang (53-69).
The importance of Asian countries towards increase of atmospheric pollutants is being examined critically in recent times. In this context, we carried out analysis of nitrates separated from aerosol samples collected during 2010 from Mt. Lulin (NOAA code: LLN), Taiwan, located at an altitude of 2 862 m above sea level. Large temporal variations are seen in δ15N, δ18O and Δ17O values of the nitrate, with day-to-day variations comparable to the seasonal amplitude. The δ15N values of nitrate are found to be higher in spring months (March–April; −1±3‰) and lower in summer (June–September; −5±3‰). Similarly, the δ18O (69 ± 15‰ versus 32 ± 13‰) and Δ17O (23 ± 5‰ versus 12 ± 4‰) values are higher in spring and lower in summer. The lowest δ18O value observed was 10.8‰. The higher values of δ15N in spring could be attributed to enhanced contribution from fossil fuel combustions, especially burning of coal in nearby Asian countries like China, with the resultant pollutants being brought to the Lulin station by long-range transport. An alternative explanation is the isotopic exchange reaction between N2O5 and HNO3 that elevates the δ15N value in nitrate. The oxygen isotope variability is explained by changes in contribution from two major pathways of nitrate formation from its precursor NO x molecules. During spring time, nitrate formation via the N2O5 pathway is dominant, resulting in higher values of both δ18O and Δ17O. In contrast, during summer, formation involving HO2/RO2 radicals becomes important, producing lower values of δ18O and Δ17O. A chemistry box model was used to study the nitrate formation pathways through oxidation of NO and NO2 via formation of NO2 and NO3 /HNO3. Both the model results and observations suggest that for the formation of NO2 from NO, the pathway via O3 is more active in spring, whereas in summer the pathway via HO2/RO2 radicals predominates. For the subsequent formation of NO3 and HNO3, the OH pathway is more active in summer than in spring. These suggestions are supported by a wind rose diagram and back trajectory analysis of air masses bringing the precursor NO x to the sampling site.
Keywords: Nitrate aerosol; Nitrogen and oxygen isotope ratios; Seasonal variation; Nitrate formation pathway analysis; Back trajectory analysis;

Molecular formula composition of β-caryophyllene ozonolysis SOA formed in humid and dry conditions by Shuvashish Kundu; Rebeka Fisseha; Annie L. Putman; Thom A. Rahn; Lynn R. Mazzoleni (70-81).
We studied the molecular formula composition of six β-caryophyllene SOA samples using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry under various reaction conditions. The SOA samples were generated in dry or low relative humidity (RH) chamber conditions with or without cyclohexane. All of the studied SOA mass spectra have three distinct clusters of hundreds of negative ions referred to as Group I (100 < m/z < 400), Group II (400 < m/z < 700) and Group III (700 < m/z < 1 000) compounds. C14-16H22-28O2-11, C28-29H42-48O6-16 and C42-43H68-70O14-16 were observed as highly abundant organic compounds in the compound class of Group I, II and III, respectively. The relative intensities of most analytes were higher in humid conditions compared to those in dry conditions, indicating the importance of water-dependent reactions and the catalytic role of water both in the presence and absence of cyclohexane. In addition, molecular formulas with higher average carbon numbers were observed in humid SOA than in dry SOA in the absence of cyclohexane, suggesting a decrease of cleavage reactions in humid condition. This study characterizes β-caryophyllene ozonolysis SOA based on ultrahigh mass resolution and demonstrates the significance of humidity in terms of the molecular distributions and relative abundances of the analytes. We also discuss the possible mechanism for the formation of Group I-III compounds based on the current understanding of SOA formation in the atmosphere.Display Omitted
Keywords: β-caryophyllene; Ozonolysis; Smog-chamber; SOA; High resolution mass spectrometry; FT-ICR;

This study presents an emission inventory (EI) for major anthropogenic sources of Indonesia in 2007 and 2010. The EI was developed using a combination of top-down and bottom-up approaches with comprehensive activity data collected at the provincial/district level to produce spatially and temporally distributed emission of toxic pollutants and greenhouse gases (GHGs). The sources were categorized into: 1) fuel combustion in power plant, 2) industry, 3) transportation, 4) residential and commercial combustion, 5) biomass open burning, and 6) non-combustion agricultural activity and waste disposal. The best estimates of the 2010 national emissions, in Gg, of toxic pollutants were: 1014 SO2; 3323 NOx; 24,849 CO; 4077 NMVOC; 1276 NH3; 2154 PM10; 1728 PM2.5; 246 BC; 718 OC; and GHGs: 540,275 CO2; 3979 CH4 and 180 N2O. During the period from 2007 to 2010, the national emissions increased by 0.7–8.8% (0.23–2.8% per year), varied with species, with the most significant changes obtained for the biomass open burning emissions. For 2010 results, the low and high emission estimates for different species were ranging from −58% to +122% of the corresponding best estimates. The largest range (high uncertainty) was for BC due to the wide range of the limitedly available emission factors. Spatially, higher emission intensity was seen in large urban areas of Java and Sumatra Islands. Temporally, dry months of August–October had higher emissions. During the first 3 years (2007–2010) of implementation, the national policy of elimination of kerosene use in cooking had successfully replaced 4.9 Tg kerosene with 2.6 Tg LPG in 30 designated provinces. The net emission reductions of different species ranged from 48 Mg (SO2) to 7.6 Tg for CO2. The global warming potential weighted emissions from the residential cooking alone, collectively for GHGs and short-lived climate pollutants in 20-yr CO2 eq., would reduce by 2%. More significant reductions in the residential combustion emissions are expected if the solid cooking fuel could be targeted in future fuel conversion programs. The benefits to human health resulted from the emission reduction of toxic pollutants from residential cooking could be substantial and should be assessed in future studies.
Keywords: Emission inventory; Air pollution; Kerosene fuel switching; Climate co-benefit; Indonesia;

Natural wetlands represent the largest single source of methane (CH4), a potent greenhouse gas. China is home to the world's fourth largest wetland area, and it is facing intense climate- and human-related impacts. The scientific community in China has invested considerable effort into investigating wetland CH4 release and its dynamics. Static chamber and eddy covariance observations have verified the temperature, water regime and air pressure as factors that regulate the diurnal and seasonal variation of CH4 release. Non-growing seasons, especially freezing–thawing cycles, play a role in CH4 release. However, a knowledge gap still exists with respect to the inter-annual variability of CH4 release. Observations also suggest that water and temperature regimes control the micro- and macro-scale spatial pattern of CH4 release, respectively. Recent bookkeeping surveys, biogeochemical model simulations, and chemical transport model inversions, have narrowed the uncertainty range of national CH4 release to 2.46–3.20, 2.77–4.95 and 2.38–4.91 Tg CH4 yr−1, respectively. Wetland loss (especially cropland conversion in Northeast China), despite climate changes, decreased CH4 release by 45.2%–52.2% from the 1950s–2000s, and by 13.2%–15.4% from the 1980s–2000s. However, future warmer temperatures and rising CO2 are predicted to strengthen national CH4 release by 32% (RCP2.6), 55% (RCP4.5) and 91% (RCP8.5) by the 2080s, albeit without the variation in wetland extent having been considered. Furthermore, future research should emphasize the mechanisms involved in CH4 release during freezing–thawing cycles and interannual variability. Model–data fusion of eddy covariance and manipulative experiments, especially warming and CO2 enrichment, would benefit estimations and projections of CH4 release.
Keywords: Methane (CH4); Natural wetland; Climate change; Land use change; China;

To better understand the impact of agricultural waste burning on the air quality of free troposphere over the North China Plain (NCP), we collected total suspended particles (TSP) at the summit of Mt. Tai, located in the NCP using a high volume air sampler during 29 May to 28 June 2006, when the field burning of agricultural residue was intense. Temporal variations of all measured species showed that their concentration increases from late May to mid June (major BB period), peaking during 12–14 June, and then significantly decreased towards late June (minor BB period). We noticed that a significant reduction in the concentrations of carbonaceous aerosols during the period of 8–11 June, when the wind direction shifted from southerly to northerly. We found that concentrations of carbonaceous aerosols and some major ions showed several times higher during major BB period than those of minor BB period. We also found that nighttime concentrations are higher than daytime during major BB period, suggesting that a long-range atmospheric transport of biomass burning plumes in the free troposphere, which arrived at the summit of Mt. Tai. In contrast, daytime concentrations are higher than nighttime during minor BB period. We found higher concentrations of secondary organic carbon (SOC) during major BB period, suggesting that formation of secondary organic aerosols through aqueous phase chemistry under high NOx conditions during a long-range atmospheric transport. nss-K+ showed about four times higher concentrations during major BB than those of minor BB. Concentrations of nss-Ca2+ are higher in nighttime during major BB period, implying that a significant long-range atmospheric transport of mineral dust over the sampling site. These results are further supported by the positive matrix factorization (PMF) analysis, which showed that biomass burning was a major source for the carbonaceous aerosols followed by mineral dust sources over the summit of Mt. Tai.Display Omitted
Keywords: Carbonaceous aerosols; Biomass burning; Mt. Tai; Temporal variation; PMF analysis;

In-flight monitoring of particle deposition in the environmental control systems of commercial airliners in China by Qing Cao; Qiuyu Xu; Wei Liu; Chao-Hsin Lin; Daniel Wei; Steven Baughcum; Sharon Norris; Qingyan Chen (118-128).
Severe air pollution and low on-time performance of commercial flights in China could increase particle deposition in the environmental control systems (ECSs) of commercial airliners. The particles deposited in the ECSs could negatively affect the performance of the airplanes. In addition, particles that penetrate into the aircraft cabin could adversely impact the health of passengers and crew members. This investigation conducted simultaneous measurements of particle mass concentration and size distribution inside and outside the cabin during 64 commercial flights of Boeing 737 and Airbus 320 aircraft departing from or arriving at Tianjin Airport in China. The results showed that the PM2.5 mass concentration deposition in the ECSs of these airplanes ranged from 50% to 90%, which was much higher than that measured in an airplane with a ground air-conditioning unit. The average deposition rates of particles with diameters of 0.5–1 μm, 1–2 μm, 2–5 μm, 5–10 μm, and >10 μm were 89 ± 8%, 85 ± 13%, 80 ± 13%, 73 ± 15%, and 80 ± 14%, respectively. The in-flight measurement results indicated that the particle concentration in the breathing zone was higher than that in the air-supply zone, which implies a significant contribution by particles in the interior of the cabin. Such particles come from human emissions or particle resuspension from interior surfaces.
Keywords: Particulate matter; Deposition; Air-conditioning system; Filtration; Particle mass; Particle number;

Particulate matter air pollution in Europe in a +2 °C warming world by Gwendoline Lacressonnière; Laura Watson; Michael Gauss; Magnuz Engardt; Camilla Andersson; Matthias Beekmann; Augustin Colette; Gilles Foret; Béatrice Josse; Virginie Marécal; Agnes Nyiri; Guillaume Siour; Stefan Sobolowski; Robert Vautard (129-140).
In the framework of the IMPACT2C project, we have evaluated the future European particulate matter concentrations under the influence of climate change and anthropogenic emission reductions. To do so, 30-year simulations for present and future scenarios were performed with an ensemble of four regional Chemical Transport Models. +2 °C scenarios were issued from different regional climate simulations belonging to the CORDEX experiment (RCP4.5 scenario). Comparing present day simulations to observations shows that these simulations meet the requested quality criteria even if some biases do exist. Also, we showed that using regional climate models instead of meteorological reanalysis was not critical for the quality of our simulations. Present day as well as future scenarios show the large variability between models associated with different meteorology and process parameterizations. Future projections of PM concentrations show a large reduction of PM10 and PM2.5 concentrations in a +2 °C climate over the European continent (especially over Benelux), which can be mostly attributed to emission reduction policies. Under a current legislation scenario, annual PM10 could be reduced by between 1.8 and 2.9 μg m−3 (14.1–20.4%). If maximum technologically feasible emission reductions were implemented, further reductions of 1.4–1.9 μg m−3 (18.6–20.9%) are highlighted. Changes due to a +2 °C warming, in isolation from emission changes, are in general much weaker (−1.1 to +0.4 μg m−3,-0.3 to +5.1% for annual PM10 averaged over the European domain). Even if large differences exist between models, we have determined that the decrease of PM over Europe associated with emission reduction is a robust result. The patterns of PM changes resulting from climate change (for example the increase of PM over Spain and southern France and the decrease of PM10 over eastern Europe) are also robustly predicted even if its amplitude remains weak compared to changes associated with emission reductions.
Keywords: Air quality; Chemical transport models; Particulate matter; Climate change; IMPACT2C project;

Tethered balloon-based particle number concentration, and size distribution vertical profiles within the lower troposphere of Shanghai by Kun Zhang; Dongfang Wang; Qinggen Bian; Yusen Duan; Mengfei Zhao; Dongnian Fei; Guangli Xiu; Qingyan Fu (141-150).
A tethered balloon-based measurement campaign of particle number concentration (PNC) and particle number size distribution (PNSD) in the size range of 15.7–661.2 nm was conducted within the lower troposphere of 1000 m in Shanghai, a Chinese megacity, during December of 2015. The meteorological conditions, PNC, and PNSD were synchronously measured at the ground-based station as well as by the tethered balloon. On ground level, the 88.2 nm particles were found to have the highest PNC. The Pearson correlation analysis based on the ground level data showed NO2 had a strong correlation with PNC. The synchronous measurement of PNC and PNSD at the ground station and on the tethered balloon showed that the 15.7–200 nm particles had higher PNC on ground level, but the PNC of 200–661.2 nm particles was higher at 400 m. One haze event (Dec 22nd-Dec 23rd) was selected for detailed discussion on the variation of vertical profiles of PNSD and PNC. The vertical distribution of characteristics of PNC and PNSD were observed and compared. Results indicated that the highest MaxDm (the diameter with the highest PNC) during those three launches all appeared at a high altitude, usually above 300 m. Compared to the clean days, the relatively bigger MaxDm at each height in the haze days also indicated regional transport of pollutants might contribute to more to that haze event.
Keywords: Vertical profile; Haze; Scanning Mobility Particle Sizers (SMPS);

Tropospheric NO2 and SO2 concentrations are of great importance with regard to air quality, atmospheric chemistry, and climate change. Due to lack of surface monitoring stations, this study analyzes long term trend of NO2 and SO2 levels (2005–2014), retrieved from Ozone Monitoring Instrument (OMI) board on the NASA's Aura satellite, in an important region of China – Henan Province. Henan Province, located in North China Plain, has encountered serious air pollution problems including extremely high PM2.5 concentrations and as one of the most polluted region in China. The satellite spatial images clearly show that high levels of both NO2 and SO2 are concentrated in north and northeastern regions with much lower levels observed in other parts of Henan. Both pollutants exhibit the highest levels in winter with the least in summer/spring. The temporal trend analysis based on moving average of deseasonalized and decyclic data indicates that for NO2, there is a continuous increasing pattern from 2005 to 2011 at 6.4% per year, thereafter, it shows a decreasing trend (10.6% per year). As for SO2, the increasing trend is about 16% per year from 2005 to 2007 with decreasing rate 7% per year from 2007 to 2014. The economic development with incredible annual 11% GDP growth in Henan is responsible for increasing levels of NO2 and SO2. The observed decreasing SO2 level starting in 2007 is due to reduced SO2 emission, utilization of flue gas desulfurization (FGD) devices and to some extent, in preparation of Beijing 2008 Olympic Games. On the other hand, increasing vehicle numbers (155% from 2006 to 2012) and coal consumption (37% during the same span), along with the lack of denitration process for removing flue/exhaust gas NOx are responsible for increasing NO2 trend until 2011. The ratio of SO2/NO2 started decreasing in 2007 and dropped significantly from 2011 to 2013 indicating good performance of FGD and ever increasing NOx contribution from mobile sources. Unlike those observed in developed countries (US, EU and Japan) where a decreasing trend for both SO2 and NO2 has been observed since 1990s, the observed upward and downward trend found in Henan is similar to those found in North China Plain and other parts of China. The spatial and temporal trend analyses of SO2 and NO2 in four other regions in Henan further indicate a similar trend to those observed in Henan Province, albeit with different increasing and decreasing rate. The results provide regulatory agency to develop action plans to combat air pollution problem in general and SO2 and NO2 problems in particular in Henan. The implications of our findings and recommendations for decision makers are discussed in the paper.Display Omitted
Keywords: OMI; SO2 and NO2; Henan province; Long term trend analysis;

To investigate on the daytime OH and its implication to fine particle, the long-path differential optical absorption spectroscopy (LP-DOAS) system was employed to observe the main OH precursors of O3, HCHO and HONO, as well as NO2 and NO3 radical from April to August 2013 over Shanghai, China. The main OH production paths from HONO, HCHO and O3 were estimated to be occupied around 57.6%, 30.5% and 11.9% during daytime. The daytime OH radical concentration under steady-state was averaged at 1.02 × 107 molec cm−3, which was significantly impacted by the photolytic processes. The relationship between photolysis frequency j(O1D) and OH radical suggests that heavy fine particle loads can make the photolytic reactions less efficiently and decrease the OH production and concentration. Utilizing CO as the indicator, the part of PM2.5 mass related to primary emitted sources was found less impacted by the OH levels. The contribution of secondary organic aerosol with metrics of O3 was enhanced with the increases of the OH levels, while secondary inorganic part of PM2.5 was favor of the condition that smaller OH concentrations that 5 × 105–5 × 106 molec cm−3. Meantime, a simplified multivariate model was employed to evaluate the influences of OH levels on different parts of fine particles related to different emission and sources. Normalized by solar radiation, this part of OH unrelated to radiation was found to be inversely related to the PM2.5, which indicates the self-cleansing capability of the atmosphere.
Keywords: OH radical; PM2.5; HONO; DOAS; Oxidation capacity;

A daily black carbon (BC) exposure assessment of forty 10-12 years-old children was conducted in the Seoul Metropolitan Area from August 2015 to January 2016. Each participant carried a micro-aethalometer to measure BC concentrations for 24 h while their whereabouts and microenvironments (MEs) were recorded via a time-activity diary (TAD) and follow-up interviews. Analysis of variance (ANOVA) was employed to compare average BC levels by potential risk factors including demographic, temporal, residential, and indoor/outdoor/transportation activity variables. The children's average daily exposure was 1.93 μg/m3, with a range of 0.2–85.43 μg/m3 (mean daily individual exposure ranges from 0.54 to 4.80 μg/m3). Even children attending the same elementary school reported BC exposures which differed by approximately 40%, primarily because of individually distinct time-activity patterns and the MEs with which each child interacted. On weekends (Saturdays and Sundays) (1.86 ± 2.50 μg/m3) and holidays (Saturdays, Sundays, and vacation) (1.71 ± 2.48 μg/m3), children were subject to reduced exposures to BC, likely due to decreased surrounding traffic volumes and different time-activity patterns on weekend days compared to on weekdays (from Mondays to Fridays) (1.95 ± 2.44 μg/m3) or school days (weekdays during the school semesters) (2.05 ± 2.43 μg/m3). Commuting in diesel vehicles (often to private academies) or in the subway, cooking, and environmental tobacco smoke were all found to elevate BC exposure. Likewise, proximity to traffic sources and parental indoor smoking contributed to the enhancement of residential BC concentrations. Our findings suggested a need to emplace proactive measures including diesel fleet regulation and smoking cessation campaigns to protect children from high levels of BC exposure.Display Omitted
Keywords: Black carbon (BC); Personal monitoring; Children; Time-activity pattern; Microenvironment (ME);

Continuous ground-based aerosol Lidar observation during seasonal pollution events at Wuxi, China by Man Sing Wong; Kai Qin; Hong Lian; James R. Campbell; Kwon Ho Lee; Shijie Sheng (189-199).
Haze pollution has long been a significant research topic and challenge in China, with adverse effects on air quality, agricultural production, as well as human health. In coupling with ground-based Lidar measurements, air quality observation, meteorological data, and backward trajectories model, two typical haze events at Wuxi, China are analyzed respectively, depicting summer and winter scenarios. Results indicate that the winter haze pollution is a compound pollution process mainly affected by calm winds that induce pollution accumulation near the surface. In the summer case, with the exception of influence from PM2.5 concentrations, ozone is the main pollutant and regional transport is also a significant influencing factor. Both events are marked by enhanced PM2.5 concentrations, driven by anthropogenic emissions of pollutants such as vehicle exhaust and factory fumes. Meteorological factors such as wind speed/direction and relative humidity are also contributed. These results indicate how the vertical profile offered by routine regional Lidar monitoring helps aid in understanding local variability and trends, which may be adapted for developing abatement strategies that improve air quality.
Keywords: Aerosol; Backward trajectory; Ground-based Lidar; Haze;

Variations in particulate matter over Indo-Gangetic Plains and Indo-Himalayan Range during four field campaigns in winter monsoon and summer monsoon: Role of pollution pathways by A. Sen; A.S. Abdelmaksoud; Y. Nazeer Ahammed; Mansour ِA. Alghamdi; Tirthankar Banerjee; Mudasir Ahmad Bhat; A. Chatterjee; Anil K. Choudhuri; Trupti Das; Amit Dhir; Pitamber Prasad Dhyani; Ranu Gadi; Sanjay Ghosh; Kireet Kumar; A.H. Khan; M. Khoder; K. Maharaj Kumari; Jagdish Chandra Kuniyal; Manish Kumar; Anita Lakhani; Parth Sarathi Mahapatra; Manish Naja; Dharam Pal; S. Pal; Mahammad Rafiq; Shakil Ahmad Romshoo; Irfan Rashid; Prasenjit Saikia; D.M. Shenoy; Vijay Sridhar; Nidhi Verma; B.M. Vyas; Mohit Saxena; A. Sharma; S.K. Sharma; T.K. Mandal (200-224).
Both in-situ and space-borne observations reveal an extremely high loading of particulates over the Indo-Gangetic Plains (IGP), all year around. With a burgeoning population and combustion sources (fossil fuels (FFs) and biofuels (BFs)) in close proximity to each other, the IGP is widely regarded as a hotspot for anthropogenic aerosol emission in South Asia. The deteriorating air quality over this region, particularly during winters, is a cause of major concern, since the pollutants undergo long range transport from their source regions to the Indo-Himalayan Range (IHR), Bay of Bengal (BoB) and other remote areas, polluting their pristine atmospheric conditions. Seasonal reversal in winds over the Indian mainland leads to an outflow of continental pollutants into the BoB during winters and a net advection of desert dust aerosols into the IGP from southwest Asia (SW-Asia), northwest India (NW-India) and northern Africa (N-Africa) during summers. Through the course of this study, four observational campaigns were conducted for sampling the ambient PM2.5 and PM10 during winter and summer seasons of 2014–2015, at multiple locations (18 sites) in the IGP, IHR, and semi-arid/arid sites towards their south and west, in order to accurately determine the inter-seasonal and inter-annual changes in the aerosol loading at the sites. We have also utilized data from Moderate Resolution Imaging Spectroradiometer (MODIS) on-board Earth Observing System (EOS) Terra satellite for estimating the columnar Aerosol Optical Depth at 550 nm (AOD550) and data from EOS Terra and Aqua satellites for discovering openly burning fires in the vicinity of sampling sites. Determination of the major source regions and key transport pathways during both seasons have also been attempted, using back-trajectory cluster analyses, as well as receptor models such as PSCF and CWT.
Keywords: PM2.5; PM10; Indo-Gangetic plains; Indo-Himalayan range; Long-range transport; Cluster analysis; PSCF; CWT;

Greenhouse gases concentrations and fluxes from subtropical small reservoirs in relation with watershed urbanization by Xiaofeng Wang; Yixin He; Xingzhong Yuan; Huai Chen; Changhui Peng; Junsheng Yue; Qiaoyong Zhang; Yuanbin Diao; Shuangshuang Liu (225-235).
Greenhouse gas (GHG) emissions from reservoirs and global urbanization have gained widespread attention, yet the response of GHG emissions to the watershed urbanization is poorly understood. Meanwhile, there are millions of small reservoirs worldwide that receive and accumulate high loads of anthropogenic carbon and nitrogen due to watershed urbanization and can therefore be hotspots of GHG emissions. In this study, we assessed the GHG concentrations and fluxes in sixteen small reservoirs draining urban, agricultural and forested watersheds over a period of one year. The concentrations of pCO2, CH4 and N2O in sampled urban reservoirs that received more sewage input were higher than those in agricultural reservoirs, and were 3, 7 and 10 times higher than those in reservoirs draining in forested areas, respectively. Accordingly, urban reservoirs had the highest estimated GHG flux rate. Regression analysis indicated that dissolved total phosphorus, dissolved organic carbon (DOC) and chlorophyll-a (Chl-a) had great effect on CO2 production, while the nitrogen (N) and phosphorus (P) content of surface water were closely related to CH4 and N2O production. Therefore, these parameters can act as good predictors of GHG emissions in urban watersheds. Given the rapid progress of global urbanization, small urban reservoirs play a crucial role in accounting for regional GHG emissions and cannot be ignored.
Keywords: GHG; Urbanization; Land use; Small reservoirs; Spatiotemporal variation; Potential controls;

Role of persistent low-level clouds in mitigating air quality impacts of wintertime cold pool conditions by Timothy M. VanReken; Ranil S. Dhammapala; B. Thomas Jobson; Courtney L. Bottenus; Graham S. VanderSchelden; Susan D. Kaspari; Zhongming Gao; Qiurui Zhu; Brian K. Lamb; Heping Liu; Jeff Johnston (236-246).
The Yakima Air Wintertime Nitrate Study (YAWNS) was conducted in January 2013 to investigate the drivers of elevated levels of fine particulate matter (PM2.5) frequently present in the region during winter stagnation periods. An extended stagnation period occurred during the study. For the first four days of the event, skies were clear and the strong diel variation in air pollution patterns were consistent with the expected effects of strong low-level nighttime temperature inversions with moderate mixing during daylight hours. Later in the event a low-level cloud layer formed that persisted over the Yakima Valley for the next seven days while regional conditions remained stagnant. Coincident with the onset of cloud, the levels of all measured primary pollutants, including CO2, CO, NOx, particle number concentration, and black carbon, dropped dramatically and remained low with negligible diel variation for as long as the cloud layer was present. The observed patterns for these air pollutants are consistent with decreased stability and enhanced mixing associated with the cloud-topped boundary layer. Interestingly, levels of secondary pollutants, most notably particulate ammonium nitrate, did not exhibit the same decline. This difference may be due to shifts in the chemical production of secondary pollutants during cloudy conditions, or may merely reflect a further influence of mixing. The results imply that the best strategies for managing wintertime air quality during episodes of persistent cloud are likely different from those needed during clear-sky stagnation events.
Keywords: Stagnation; Cloud-topped boundary layer; Wintertime air quality; Aerosol nitrate;

Gaseous mercury fluxes in peatlands and the potential influence of climate change by Kristine M. Haynes; Evan S. Kane; Lynette Potvin; Erik A. Lilleskov; Randall K. Kolka; Carl P.J. Mitchell (247-259).
Climate change has the potential to significantly impact the stability of large stocks of mercury (Hg) stored in peatland systems due to increasing temperatures, altered water table regimes and subsequent shifts in vascular plant communities. However, the Hg exchange dynamics between the atmosphere and peatlands are not well understood. At the PEATcosm Mesocosm Facility in Houghton, Michigan, total gaseous Hg (TGM) fluxes were monitored in a subset of 1-m3 peat monoliths with altered water table positions (high and low) and vascular plant functional groups (sedge only, Ericaceae only or unmanipulated control) above the Sphagnum moss layer. At the SPRUCE bog in north-central Minnesota, TGM fluxes were measured from plots subjected to deep peat soil warming (up to +9 °C above ambient at a depth of 2 m). At PEATcosm, the strongest depositional trend was observed with the Low WT – sedge only treatment mesocosms with a mean TGM flux of −73.7 ± 6.3 ng m−2 d−1, likely due to shuttling of Hg to the peat at depth by aerenchymous tissues. The highest total leaf surface and tissue Hg concentrations were observed with the Ericaceae shrubs. A negative correlation between TGM flux and Ericaceae total leaf surface area suggests an influence of shrubs in controlling Hg exchange through stomatal uptake, surface sorption and potentially, peat shading. Surface peat total Hg concentrations are highest in treatments with greatest deposition suggesting deposition controls Hg accumulation in surface peat. Fluxes in the SPRUCE plots ranged from −45.9 ± 93.8 ng m−2 d−1 prior to the implementation of the deep warming treatments to −1.41 ± 27.1 ng m−2 d−1 once warming targets were achieved at depth and +10.2 ± 44.6 ng m−2 d−1 following prolonged deep soil warming. While these intervals did not differ significantly, a significant positive increase in the slope of the regression between flux and surface temperature was observed across the pre-treatment and warming periods. Shifts in vascular vegetation cover and peat warming as a result of climate change may significantly affect the dynamics of TGM fluxes between peatlands and the atmosphere.Display Omitted
Keywords: Hg; Total gaseous mercury flux; Wetland; Soil warming; Water table; Plant community; Climate change;

Emission factors and characteristics of ammonia, hydrogen sulfide, carbon dioxide, and particulate matter at two high-rise layer hen houses by Ji-Qin Ni; Shule Liu; Claude A. Diehl; Teng-Teeh Lim; Bill W. Bogan; Lide Chen; Lilong Chai; Kaiying Wang; Albert J. Heber (260-273).
Air pollutants emitted from confined animal buildings can cause environmental pollution and ecological damage. Long-term (>6 months) and continuous (or high frequency) monitoring that can reveal seasonal and diurnal variations is needed to obtain emission factors and characteristics about these pollutants. A two-year continuous monitoring of ammonia (NH3), hydrogen sulfide (H2S), carbon dioxide (CO2) and particulate matter (PM10) emissions from two 218,000-hen high-rise layer houses (H-A and H-B) in Indiana, USA was conducted from June 2007 to May 2009. Gaseous pollutant concentrations were measured with two gas analyzers and PM10 concentrations were measured with three Tapered Element Oscillating Microbalances. The operation and performance of ventilation fans were continuously monitored with multiple methods. Only the emission rates calculated with valid data days (days with more than 18 h, or 75%, of valid data) are reported in this paper. The two-house and two-year mean ± standard deviation emissions per day per hen for NH3, H2S, CO2, and PM10 were 1.08 ± 0.42 g, 1.37 ± 0.83 mg, 76.7 ± 14.6 g, and 20.6 ± 22.5 mg, respectively. Seasonal emission variations were demonstrated for NH3 and CO2, but not evident for H2S and PM10. Ammonia and CO2 emissions were higher in winter than in summer. Significant daily mean emission variations were observed for all four pollutants between the two houses (P < 0.05), and between the two years from the same house (P < 0.01) except for CO2 at one house. Carbon dioxide originated from manure decomposition was >9% of that from bird respiration. Emissions of CO2 during molting were about 80% of those during normal egg production days. Emissions of H2S were not a major concern due to their very low quantities. Emissions of PM10 were more variable than other pollutants. However, not all of the emission statistics are explainable.Display Omitted
Keywords: Agricultural air quality; Animal agriculture; Air pollution; Emission baseline; Pollutant emission; Poultry house;

Field comparison of instruments for exposure assessment of airborne ultrafine particles and particulate matter by Andrea Spinazzè; Giacomo Fanti; Francesca Borghi; Luca Del Buono; Davide Campagnolo; Sabrina Rovelli; Andrea Cattaneo; Domenico M. Cavallo (274-284).
The objective of this study was to compare the use of co-located real-time devices and gravimetric samplers to measure ultrafine particles (UFP) and size-fractionated PM mass concentrations. The results contribute to evaluating the comparability of different monitoring instruments for size-fractionated PM concentrations. Paired light scattering devices and gravimetric samplers were used to measure the PM1, PM2.5, PM4/5, PM10 and TSP mass concentrations during 8-h monitoring sessions in an urban background site (Como, Italy) in winter. A total of 16 sampling sessions were performed: measurements were analyzed using linear regression analysis. Absolute deviations between techniques were calculated and discussed. The UFP concentrations measured using a condensation particle counter were clearly overestimated compared with the reference instrument (portable diffusion charger), with an absolute deviation that appeared to increase with the UFP concentration. The comparison of different light-scattering devices (photometers - ‘PHOTs’) indicated an over-estimation of two of the tested instruments (PHOT-2 and PHOT-3) with respect to the one used as the reference (PHOT-1) regarding the measurement of the size-fractioned PM, with the only exception being PM4/5. Further, the comparison of different light-scattering devices with filter-based samplers indicated that direct-reading devices tend to over-estimate (PHOT-2, PHOT-3) or under-estimate (PHOT-1) the PM concentrations from gravimetric analysis. The comparison of different filter-based samplers showed that the observed over-estimation error increased with increasing PM concentration levels; however, the good level of agreement between the investigated methods allowed them to be classified as comparable, although they cannot be characterized as having reciprocal predictability. Ambient relative humidity was correlated with the absolute error resulting from the comparison of direct-reading vs. filter-based techniques, as well as among different filter-based samplers for the same PM fraction.
Keywords: Urban background; PM concentration; Gravimetric analysis; Direct reading instrument; Intercomparison;

Assessment of discrepancies between bottom-up and regional emission inventories in Norwegian urban areas by Susana López-Aparicio; Marc Guevara; Philippe Thunis; Kees Cuvelier; Leonor Tarrasón (285-296).
This study shows the capabilities of a benchmarking system to identify inconsistencies in emission inventories, and to evaluate the reason behind discrepancies as a mean to improve both bottom-up and downscaled emission inventories. Fine scale bottom-up emission inventories for seven urban areas in Norway are compared with three regional emission inventories, EC4MACS, TNO_MACC-II and TNO_MACC-III, downscaled to the same areas. The comparison shows discrepancies in nitrogen oxides (NOx) and particulate matter (PM2.5 and PM10) when evaluating both total and sectorial emissions. The three regional emission inventories underestimate NOx and PM10 traffic emissions by approximately 20–80% and 50–90%, respectively. The main reasons for the underestimation of PM10 emissions from traffic in the regional inventories are related to non-exhaust emissions due to resuspension, which are included in the bottom-up emission inventories but are missing in the official national emissions, and therefore in the downscaled regional inventories. The benchmarking indicates that the most probable reason behind the underestimation of NOx traffic emissions by the regional inventories is the activity data. The fine scale NOx traffic emissions from bottom-up inventories are based on the actual traffic volume at the road link and are much higher than the NOx emissions downscaled from national estimates based on fuel sales and based on population for the urban areas. We have identified important discrepancies in PM2.5 emissions from wood burning for residential heating among all the inventories. These discrepancies are associated with the assumptions made for the allocation of emissions. In the EC4MACs inventory, such assumptions imply high underestimation of PM2.5 emissions from the residential combustion sector in urban areas, which ranges from 40 to 90% compared with the bottom-up inventories. The study shows that in three of the seven Norwegian cities there is need for further improvement of the emission inventories.
Keywords: Emission inventories; Benchmarking system; Urban scale; Downscaled emissions; Bottom-up emissions;

Composition of the secondary organic aerosol (SOA) generated during ozonolysis of limonene was investigated with liquid chromatography coupled to the negative electrospray ionization (ESI), quadrupole tandem mass spectrometry (MS/MS) as well as high resolution Time-of-Flight mass spectrometry. Aerosol was generated in the flow-tube reactor. HR-MS/MS analysis allowed for proposing structures for the several up-to-date unknown limonene oxidation products. In addition to the low MW limonene oxidation products, significant quantities of oligomers characterized by elemental compositions: C19H30O5, C18H28O6, C19H28O7, C19H30O7 and C20H34O9 were detected in the SOA samples. It was concluded that these compounds are most likely esters, aldol reaction products and/or hemiacetals. In addition to detailed study of the limonene oxidation products, the reaction time as well as initial ozone concentration impact on the limonene SOA composition was investigated. The relative intensities of the two esters of the limonic acid and 7-hydroxy limononic acid increased as a result of lowering the initial ozone concentration and shortening the reaction time, indicating that esterification may be an important oligomerization pathway during limonene SOA formation.
Keywords: Limonene; Secondary organic aerosol; Ozone; Tandem mass spectrometry; Electrospray ionization; Oligomers;

A new passive sampler for collecting atmospheric tritiated water vapor by Bin Feng; Bo Chen; Weihai Zhuo; Weiyuan Zhang (308-317).
A new passive sampler was developed for collecting environmental tritiated water vapor. The construction of the sampler was improved according to computational fluid dynamics (CFD) simulations in which the influence on vapor collection by the turbulence inside the sampler was considered. Through changes in temperature from 5 °C to 35 °C and relative humidity from 45% to 90%, the new sampler revealed stable performance of the sampling rate. Compared with the previous samplers, the new sampler significantly lowered the effect of wind speed. Using the adsorption kinetic curve of the sampler provided in the co-comparison experiments, the quantitative relationship between the mass of adsorbed water and the cumulative absolute humidity exposure was established. Field applications in the vicinity of a nuclear power plant show that the data obtained by the new samplers is consistent with the active measurement. The sampler was preliminarily proven to be reliable and flexible for field investigation of HTO in the atmosphere.
Keywords: Passive sampler; HTO; CFD; Sampling rate; Meteorological factors;

It is important to determine the distribution of solar radiation between the top of the atmosphere and the surface. Based on an empirical model for estimating hourly ultraviolet radiation irradiance (UVI) under all sky conditions in North China, UVI at the surface and at the top of the atmosphere were obtained. An important phenomenon of UV utilization by “water vapor or absorbing factor” in the 290–400 nm range was studied, its mechanism was that UV energy can be absorbed indirectly once they react OH radicals and H2O and/or consumed directly by gases, liquids, particles (GLPs). The UVI loss in the atmosphere contributed by “absorbing” and scattering materials were 19.30 and 35.31 W m−2, respectively, which depend on the region and season. The energy loss related to the “absorbing substances” would exist in other regions and should be considered in models (e.g., radiative transfer, chemistry and photochemistry, climate) for better understanding the basic processes in the atmosphere.
Keywords: UV absorption; UV scattering; Energy; OH radical; Chemical reactions; Photochemical reactions;

Size-resolved characterization of the polysaccharidic and proteinaceous components of sea spray aerosol by Josephine Y. Aller; JoAnn C. Radway; Wendy P. Kilthau; Dylan W. Bothe; Theodore W. Wilson; Robert D. Vaillancourt; Patricia K. Quinn; Derek J. Coffman; Benjamin J. Murray; Daniel A. Knopf (331-347).
Dissolved organic polymers released by phytoplankton and bacteria abiologically self-assemble in surface ocean waters into nano-to micro-sized gels containing polysaccharides, proteins, lipids and other components. These gels concentrate in the sea surface microlayer (SML), where they can potentially contribute to sea spray aerosol (SSA). Sea spray is a major source of atmospheric aerosol mass over much of the earth's surface, and knowledge of its properties (including the amount and nature of the organic content), size distributions and fluxes are fundamental for determining its role in atmospheric chemistry and climate. Using a cascade impactor, we collected size-fractionated aerosol particles from ambient air and from freshly generated Sea Sweep SSA in the western North Atlantic Ocean together with biological and chemical characterization of subsurface and SML waters. Spectrophotometric methods were applied to quantify the polysaccharide-containing transparent exopolymer (TEP) and protein-containing Coomassie stainable material (CSM) in these particles and waters. This study demonstrates that both TEP and CSM in surface ocean waters are aerosolized with sea spray with the greatest total TEP associated with particles <180 nm in diameter and >5 000 nm. The higher concentrations of TEP and CSM in particles >5 000 nm most likely reflects collection of microorganism cells and/or fragments. The greater concentration of CSM in larger size particles may also reflect greater stability of proteinaceous gels compared to polysaccharide-rich gels in surface waters and the SML. Both TEP and CSM were measured in the ambient marine air sample with concentrations of 2.1 ± 0.16 μg xanthan gum equivalents (XG eq.) m3 and 14 ± 1.0 μg bovine serum albumin equivalents (BSA eq.) m−3. TEP in Sea Sweep SSA averaged 4.7 ± 3.1 μg XG eq. m−3 and CSM 8.6 ± 7.3 μg BSA eq. m−3. This work shows the transport of marine biogenic material across the air-sea interface through primary particle emission and the first demonstration of particle size discriminated TEP and CSM characterization of SSA and ambient aerosol under field conditions.Display Omitted
Keywords: Sea surface microlayer; Transparent exopolymer material; Protein-containing gel particles; Sea spray aerosol; MOUDI;

10-Month characterization of the aerosol number size distribution and related air quality and meteorology at the Bondville, IL Midwestern background site by Robert L. Bullard; Ashish Singh; Sybil M. Anderson; Christopher M.B. Lehmann; Charles O. Stanier (348-361).
The aerosol size distribution was measured at a rural continental U.S. location (Bondville, Illinois 40.05N and 88.37W) for the period July 2013–June 2014. The dehumidified size distribution in the range 3 nm to 2.5 μm was continuously recorded by two scanning mobility particle sizers and an aerodynamic particle sizer. The Illinois measurement site is significant because it is home to one of the longest records (20+ years) in North America of atmospheric aerosol, meteorology, and gas phase variables. It is a common site for model-measurement comparison of both chemical and aerosol microphysical variables. However, while the measurement record has aerosol number concentration and optical properties, the number size distribution has not been well-constrained. Measurement highlights include means in number concentration (3–2500 nm), aerosol optical depth, S O 2 , N H 3 , and PM 2.5 of 6500 cm−3, 0.18, 0.87 ppb, 1.6 ppb, and 8.8 μg m−3, respectively. The mode in the mean size distribution was 31 nm (number) and 287 nm (volume). The mean size distribution was heavily influenced by nuclei mode particles, with 46% of particles smaller than 20 nm. New particle formation and growth events increase midday concentrations of 3–50 nm particles substantially, with the highest activity in spring months and lower activity in summer and winter. Short term elevations in particle number and mass associated with local agricultural burning in April are reported as well.Display Omitted
Keywords: Ultrafine particles; Nucleation; Bondville; PM 2.5 ; Air quality; Number size distribution;