Wide-range Particle Spectrometer Research Articles

Detection of aerosol mass concentration profiles using single-wavelength Raman Lidar within the planetary boundary layer

Considering the importance of the aerosol optical parameters detection for environmental monitoring, a method of converting single-wavelength Raman lidar backscattered echoes to aerosol mass concentrations is proposed to obtain a high-resolution vertical distribution of particulate matter (PM) mass concentrations. PMx (x = 1, 2.5, 10) mass concentrations and extinction coefficients at 355 nm and 532 nm were obtained using a combination of a colocated visibility meter and wide-range particle spectrometer (WRAS), and parameterized equations between the aerosol extinction coefficient and mass concentration at different levels of relative humidity (RH) were established (the sample datasets included different seasonal and weather pollution conditions in Xi'an, China, for 2018 and 2019). The results demonstrate that parametric analysis of sample datasets at three levels of RH (RH < 60%, 60% ≤ RH < 75%, and RH ≥ 75%) can better reflect the long-term variation characteristics of aerosols: the aerosol extinction coefficients show an exponential relationship with PM1 and PM2.5 mass concentrations, and the correlation coefficients are both above 0.965 even at different levels of RH, while the correlation with PM10 is 0.808. The extinction coefficient and RH profiles can be retrieved using single-wavelength Raman lidar, and then the aerosol mass concentration distribution can be calculated by combining parameterized equations. The deviation of mass concentration profiles between 355 and 532 nm Raman lidar was analyzed, and it is a constraint that the calculation of the PM mass concentration profile is made in the planetary boundary layer (PBL). The derivation uncertainty of PMx and the limitations of the method are also discussed. Finally, cases of vertical distribution and variations in PMx on pollution-free and hazy days are presented.

Factors Influencing New Atmospheric Particle Formation in Ordos During Summer and Autumn 2019

In this study, the aerosol number size distribution in the range of 10 nm-10 μm was collected from August 16 to October 04, 2019 at Ordos using a wide-range particle spectrometer (WPS). Combined with PM (PM2.5 and PM10), pollution gases, meteorological data, and the HYSPLIT model, the characteristics and impact factors of new particle formation (NPF) were discussed. The results indicated that there were 19 NPF events during the observation period, which have different effects on diurnal variation in aerosol number concentration in different modes. The NPF events caused a sharp increase in the number concentration of nucleation and Aitken mode aerosols, but had little effect on the number concentration of accumulation and coarse mode aerosols. The temperature, wind speed, and total solar radiation during NPF days were usually higher than those in non-NPF days, and the RH during NPF days was lower. On NPF days, the mass concentrations of PM2.5, PM10, CO, and NO2 were lower than those on non-NPF days, while the mass concentrations of O3 and SO2 were higher. NPF events were observed in 40.0% of northern air masses and 29.6% of southern air masses. There were significant differences in meteorological elements in different NPF event air mass types. The southern NPF event air mass type had the lowest wind speed and the highest RH, with averages of (2.4±1.5) m·s-1 and (48.8±10.8)%, respectively. The northern NPF event air mass type had the highest wind speed and total solar radiation, with averages of (4.2±1.9) m·s-1 and (664.5±255.6) W·m-2, respectively. The western air mass type of NPF event had the lowest RH, with an average of (29.8±12.7)%. The formation rates of new particles in the different air mass types of NPF events were similar, ranging from 1.5 to 1.8 cm-3·s-1. The largest growth rate was (12.7±13.6) nm·h-1 in the southern NPF event air mass type, which was 1.2 times and 1.4 times higher than the NPF events of northern air masses and western air masses.

Distribution Characteristics of Aerosol Size and CCN during the Summer on Mt. Tian and Their Influencing Factors

The aerosol size distribution and cloud condensation nuclei (CCN) number concentration were measured using a wide-range particle spectrometer (WPS) and a cloud condensation nuclei counter (CCNC) on Mt. Tian from 31 July to 9 September, 2019. Combined with meteorological data, distribution characteristics of aerosol size and CCN and their influencing factors were analyzed. The results indicated that the mean aerosol number concentration was 5475.6 ± 5636.5 cm−3. The mean CCN concentrations were 183.7 ± 114.5 cm−3, 729.8 ± 376.1 cm−3, 1630.5 ± 980.5 cm−3, 2162.5 ± 1345.3 cm−3, and 2575.7 ± 1632.9 cm−3 at supersaturation levels of 0.1%, 0.2%, 0.4%, 0.6%, and 0.8%, respectively. The aerosol number size distribution is unimodal, and the dominant particle size is 30–60 nm. Affected by the height of the boundary layer and the valley wind, the diurnal variation in aerosol number concentration shows a unimodal distribution with a peak at 17:00, and the CCN number concentration showed a bimodal distribution with peaks at 18:00 and 21:00. The particle size distribution and supersaturation have a major impact on the activation of the aerosol into CCN. At 0.1% supersaturation (S), the 300–500 nm particles are most likely to activate to CCN. Particles of 100–300 nm are most easily activated at 0.2% (S), while particles of 60–80 nm are most likely activated at high supersaturation (≥0.4%). The concentrations of aerosol and CCN are higher in the northerly wind. Ambient relative humidity (RH) has little relationship with the aerosol activation under high supersaturation. According to N = CSk fitting the CCN spectrum, C = 3297 and k = 0.90 on Mt. Tian, characteristic of the clean continental type.

Characteristics of Aerosol during a Severe Haze-Fog Episode in the Yangtze River Delta: Particle Size Distribution, Chemical Composition, and Optical Properties

Particle size distribution, water soluble ions, and black carbon (BC) concentration in a long-term haze-fog episode were measured using a wide-range particle spectrometer (WPS), a monitor for aerosols and gases (MARGA), and an aethalometer (AE33) in Nanjing from 16 to 27 November, 2018. The observation included five processes of clean, mist, mix, haze, and fog. Combined with meteorological elements, the HYSPLIT model, and the IMPROVE model, we analyzed the particle size distribution, chemical composition, and optical properties of aerosols in different processes. The particle number size distribution (PNSD) in five processes differed: It was bimodal in mist and fog and unimodal in clean, mix, and haze. The particle surface area size distribution (PSSD) in different processes showed a bimodal distribution, and the second peak of the mix and fog processes shifted to a larger particle size at 480 nm. The dominant air masses in five processes differed and primarily originated in the northeast direction in the clean process and the southeast direction in the haze process. In the mist, mix, and fog processes local air masses dominated. NO3− was the primary component of water soluble ions, with the lowest proportion of 45.6% in the clean process and the highest proportion of 53.0% in the mix process. The ratio of NH4+ in the different processes was stable at approximately 23%. The ratio of SO42− in the clean process was 26.2%, and the ratio of other processes was approximately 20%. The average concentration of BC in the fog processes was 10,119 ng·m−3, which was 3.55, 1.80, 1.60, and 1.46 times that in the processes of clean, mist, mix, and haze, respectively. In the different processes, BC was primarily based on liquid fuel combustion. NO3−, SO42−, and BC were the main contributors to the atmospheric extinction coefficient and contributed more than 90% in different processes. NO3− contributed 398.43 Mm−1 in the mix process, and SO42− and BC contributed 167.90 Mm−1 and 101.19 Mm−1, respectively, during the fog process.

Size Distributions of Aerosol During the Summer at the Summit of Mountain Taishan (1534 m) in Central East China

In this study, the size distribution of aerosol number concentration (10 nm-10μm), particulate matter (PM2.5 and PM10), and meteorological data were collected from June 1 to 25, 2017, at the summit of Mountain Taishan by using a wide-range particle spectrometer (WPS), a β-ray continuous ambient particulate monitor, and an automatic weather station. Consequently, the characteristic of the aerosol size distribution and their impact factors were analyzed. The results indicated that the average mass concentration of PM2.5 and PM10 were 20.7 μg·m-3 and 82.4 μg·m-3, respectively, and the ratio of PM2.5/PM10 was only 25.1%. The average number concentration, surface area concentration, and volume concentration were 8672.8 cm-3, 408.3μm2·cm-3, and 24.2μm3·cm-3, respectively. The spectrum distribution was unimodal for number concentration, and trimodal for surface area and volume concentration. The dominant sizes of the number concentration and the surface area concentration were located at 10-20 nm and 100-500 nm, respectively. The volume concentration had dominant sizes at 100-500 nm and 2.5-10 μm. Wind direction was proved to have a greater influence on PM and number concentration compared with wind speed. With the enhancement of RH, the spectrum of number concentration was converted from bimodal to unimodal distribution, while the surface area concentration changed from unimodal to trimodal distribution.

Characteristics of Aerosol Chemical Compositions and Size Distributions during a Long-Range Dust Transport Episode in an Urban City in the Yangtze River Delta

A long- and large-range heavy dust episode occurred from 3 to 8 May 2017 in China. To explore the impacts of this long-range dust transport episode on the chemical compositions and size distributions of urban aerosols, such instruments as an online analyzer for monitoring aerosols and gases (MARGA) and a wide-range particle spectrometer (WPS) were mainly used to monitor chemical components, such as PM2.5 and aerosol size distributions in the range of 10 nm to 10 μm, in Nanjing in this study. During the dust episode, the average concentrations of PM2.5 and PM10 and ions of Ca2+, Mg2+, Cl-, SO42−, NO3−, and NH4+ were 66.2, 233.9, and 1.1, 1.5, 1.1, 11.4, 7.8 and 4.4 μg·m−3, which were 4.4, 5.8, 3.7, 15, 1.38, 1.84, 1.66 and 1.83 times higher than the values observed before the episode and 2.2, 3.3, 5.5, 5.0, 1.57, 1.97, 1.39 and 1.69 times the levels after the episode. The dusts were demonstrated to have differential impacts on the water-soluble gases in the air. During the dust episode, the concentrations of HCl, SO2 and NH3 were comparably low, while the HNO2 and HNO3 concentrations were high. The diurnal variations in pollutants, including SO2, HNO3, Cl−, Ca2+, Mg2+, PM2.5 and PM10, were strongly impacted by the dust episode. However, those variations in NH3, NO3−, SO42− and NH4+ were only slightly influenced. Pollutants were distinctively featured in the various dust stages. The concentration of HNO2 was relatively high in the earliest stage but was substituted by those of SO2, PM10, PM2.5, Ca2+, Mg2+ HNO3 and Cl- in the explosion stage. The aerosol number concentrations exhibited unimodal distributions in the earliest and explosion stages but showed bimodal distributions in the duration and dissipation stages. Additionally, the aerosol size distributions were observed to shift to larger particle segments in different dust stages. The surface area concentrations exhibited four peaks in different dust stages and exhibited trimodal distributions in the non-dust episode. The surface area concentration of fine particles first increased during the earliest stage, while that of coarse particles first decreased during the dissipation stage.

Observation of atmospheric new particle growth events at the summit of mountain Tai (1534 m) in Central East China

New particle formation (NPF) and growth is an important phenomenon in terms of the global particle number concentrations. However, our knowledge about NPF events at the top of the boundary layer is particularly weak in heavily polluted conditions. In this study, the aerosol size distributions, black carbon (BC), chemical components of single particles, particulate matter (PM2.5 and PM10) and meteorological data were collected from May 12 to June 8, 2017 at the summit of Mt. Tai by using a wide-range particle spectrometer (WPS), Aethalometer (AE-33), a single particle aerosol mass spectrometer (SPAMS), a β-ray continuous ambient particulate monitor and an automatic weather station. Twelve new particle growth (NPG) events occurred during the observation period, accounting for 46.2% of the total observation days. The average relative humidity (RH) was 52% on NPF days and was 11.5% lower than the value on non-NPG days. The average temperature and wind speed were 18 °C and 5.3 m s−1 on NPG days, respectively, which were 12.2% and 18.9% higher than those on non-NPG days. The PM2.5 concentration differed slightly on NPG and non-NPG days. However, the concentrations of PM10 and BC were relatively high on NPG days, with average values of 88.0 μg m−3 and 1849.9 ng m−3, respectively, which were 1.2 and 1.3 times higher than those on non-NPG days. The NPG events had major influences on the size distributions of aerosol number concentration at 10–60 nm and surface area concentrations at 100–300 nm. During the NPG events, the average formation rate (FR), growth rate (GR), condensational sink (CS), vapor source rate (Q) and condensing vapor concentration (C) were calculated to be 1.30 cm−3 s−1, 14.54 nm h−1, 3.21 × 10−2 s−1, 7.34 × 106 cm−3 s−1 and 19.92 × 107 cm−3, respectively. The NPG events were influenced mostly by foreign transport processes and less impacted by local surrounding pollutants. The meteorological factors varied with different types of NPG events. The chemical components varied greatly during different types of NPG events. Sulfate had a small influence on three types of NPG events. Nitrate and ammonium had comparatively great impacts on local and southerly transport NPG events. The organic matters contributed more significantly to the northerly transport NPG events.

Size distribution of bioaerosols from biomass burning emissions: Characteristics of bacterial and fungal communities in submicron (PM1.0) and fine (PM2.5) particles

The North China Plain is the agricultural heartland in China. High PM2.5 levels and elevated chemical pollutants have been observed during crop harvest seasons due to open biomass burning. Biomass burning in the wheat-harvest season may significantly deteriorate the regional air quality. The harmful ingredients in smoke particles also have severe implications for toxicity and health effects. Previous studies have illustrated the potential role of bioaerosols as ice-nuclei and cloud condensation nuclei and highlighted their influence on biochemical cycles and human health effects. In a monthly field observation campaign of biomass burning conducted at the summit of Mount Tai in July 2015, we reported the composition, potential role, size distribution of microorganisms in particulate matters PM1.0, PM2.5, and estimated their contribution to particles. The wide-range particle spectrometer suggested that the predominant particles were distributed in submicron particles (PM1.0), which resulted in a similar community structure for bacteria and fungi in PM1.0 and PM2.5. Among bacteria, the predominant Pseudomonas accounted for 18.06% and 21.29% in PM1.0 and PM2.5, respectively. Alternaria covered up to 69.01% and 72.76% of the fungal community in PM1.0 and PM2.5, respectively. A disparity between bacterial communities was identified by the abundance of rare species, such as Bacilli being higher in PM1.0 (2.4%) than in PM2.5 (1.8%), and Defluviicoccus being higher in PM2.5 (2.5%) than in PM1.0 (0.5%), which may be related to cell size and cell growth patterns. Quantitative PCR revealed that microbial cell numbers in PM2.5 were higher than in PM1.0, and that the bacterial cell number was about an order of magnitude greater than the fungal cell number. However, the mass concentration and contribution of fungi to particulate matter was much higher than that of bacteria, suggesting the underestimated role of fungi in atmospheric aerosols. Airborne microorganisms in alpine areas remained less characterized. The findings presented here illustrated the potentially important impacts on air quality and bioaerosol pollution by biomass burning, which provides an essential reference for understanding the transmission and health effects of bioaerosols.

Source Apportionment and Size Distribution of Aerosols at Lin'an Atmosphere Regional Background Station During Winter

Using a wide-range particle spectrometer (WPS), an environmental management system (EMS), KC-120H middle volume sampler, a 850 professional ion chromatography analyzer, and heat/light carbon analyzer (DRI2001A), we observed the number concentration of aerosols with sizes ranging from 10 nm to 10 μm, gas concentrations, and concentrations of PM2.5, water-soluble ions, OC, and EC in a Lin'an atmospheric background station from January 9 to 31, 2015. The positive matrix factorization (PMF) model was applied for source apportionment, and the size distribution and diurnal variations of emission sources were analyzed based on the meteorological data. The average aerosol concentration was 5062 cm-3·nm-1 and PM2.5 mass concentration was 123.6 μg·m-3. The average concentrations of NO3-, SO42-, and NH4+, the main water-soluble ions in PM2.5 were 19.2, 15.4, and 10.8 μg·m-3, which accounted for 37.9%, 30.4%, and 21.4% of total water-soluble ions, respectively. Theaverage concentrations of OC and EC were 24.4 μg·m-3 and 6.6 μg·m-3. Secondary aerosol formation, coal combustion, motor vehicle emissions, dust, andbiomass burning were the main sources of PM2.5 in Lin'an during winter with contributions of 42.3%, 21.4%, 17.1%, 8.7%, and 10.6%, respectively. Different sources had different aerosol number concentration distributions. The aerosol number concentration spectra of secondary sources, vehicle emissions, dust, and biomass burning followed unimodal-type distributions with peaks at 120, 50, 100, and 90 nm. Coal particle number concentration was a bimodal distribution which exhibited peak values at 25 nm and 100 nm (19842 cm-3·nm-1 and 18372 cm-3·nm-1, respectively). The spectra of surface concentrations of secondary sources, coal combustion, motor vehicle emissions, dust, and biomass burning followed a three-peak distribution. The peaks were at 650, 210, 160, 180, and 575 nm. The diurnal variations of particle number concentrations influenced by diurnal variations in the boundary layer and human activities were consistent with the variations in surface concentrations, which displayed bimodal-type distribution.

Distribution Characteristics of Air Pollutants and Aerosol Chemical Components Under Different Weather Conditions in Jiaxing

Distribution characteristics of air pollutants and aerosol chemical components under different weather conditions were investigated in Jiaxing between May 1 and 31, 2015. The particulate matter (PM), gaseous pollutants, chemical components in PM1.0, and aerosol number concentrations ranging from 10 nm to 10 μm were measured using the SHARP-5030 monitoring instrument, Thermo EMS system, Aerodyne Aerosol Chemical Speciation Monitor (ACSM), and Wide-Range Particle Spectrometer (WPS), respectively. The average concentrations of PM2.5, PM1.0, SO2, NO2, O3, and CO were 52.8 μg·m-3, 37.2 μg·m-3, 10.3 μg·m-3, 38.1 μg·m-3, 92.1 μg·m-3, and 1.2 mg·m-3 during the observation period. The chemical components of OA, SO42-, NO3-, NH4+, and Cl-in PM1.0 had average concentrations of 2.18, 1.24, 0.87, 0.63, and 0.08 μg·m-3, respectively. The aerosol number concentrations were mainly centralized in Aitken mode (20-100 nm), with a value of 12411.2 cm-3. The nuclei mode aerosols (10-20 nm) followed the number concentrations with 4946.6 cm-3. The concentration distributions and diurnal variations of PM and gaseous pollutants, and the distributions of chemical components of PM1.0 varied under different weather conditions. The concentrations of chemical components were ranked in the order of OA > SO42- > NO3- > NH4+ > Cl- on rainy days and sunny days, and in the order of OA > NO3- > SO42- > NH4+ > Cl- on new particle formation (NPF) days. The OA and NO3- concentrations on NPF days were 1.61 and 1.42 times larger than those on sunny days, suggesting that the components of OA and NO3- were the main substances influencing the NPF events. Additionally, the diurnal variations of aerosols in different modes varied under different types of weather conditions.

Modeled Deposition of Fine Particles in Human Airway in Northern Suburb of Nanjing

The particles number concentrations were determined by Wide-range Particle Spectrometer (WPS) in northern suburb of Nanjing in January and April 2015. The information of size distributions was applied in the multiple-path particle dosimetry model (MPPD) v.3.04 to quantify deposition fractions (DF) and number concentration (NC) depositions of fine particles in different regions of human airway, at different air quality levels, at rest and exercise. DF of nucleation mode and Aitken mode at rest and exercise were similar, while DF of accumulation mode at exercise was 2.49 times of that at rest. DF of nucleation mode and Aitken mode in pulmonary (PUL) was the highest, about 48.17% of total deposition fractions (TDF) at rest and 54.23% of TDF at exercise. DF of accumulation mode in head was the highest, about 41.23% of TDF at rest and 80.47% of TDF at exercise. The particle NC deposition in human airway in winter was lower than that in spring, and the total NC deposition in 3 regions was in the order of PUL > tracheobronchial(TB) > head. Compared with resting, nucleation mode deposition in PUL and accumulation mode deposition in TB and head increased at exercise. The worse the air quality, the higher the deposition growth rate of exercising to resting in head. DF difference among regions was mainly due to the different physiological parameters, while NC deposition difference was mainly due to the different particle NC in the local environment.

Effect of ultrasonic frequency on size distributions of nanosized mist generated by ultrasonic atomization

Ultrasonic atomization is used to produce fine liquid mists with diameter ranges below 100nm. We investigated the effect of the frequency on the size distribution of ultrasonic mist. A bimodal distribution was obtained for the mist generated by ultrasonic atomization with a wide-range particle spectrometer. The peak diameter decreased with increasing frequency, and the number concentration of the mist increased in the smaller range. We determined the relation between the size distribution of the mist and the ultrasonic frequency, and we proposed a generation mechanism for the ultrasonic nanosized mist based on the amount of water vapor around the liquid column. Increasing the power intensity and density by changing the surface diameter of the ultrasonic oscillator affected the number concentration and size distribution of the nanosized mist. Using this technique, the diameter of the mist can be controlled by changing the frequency of the ultrasonic transducer.

Effects of amines on particle growth observed in new particle formation events

AbstractParticle size distributions in the range of 0.01–10 µm were measured in urban Shanghai in the summer of 2013 using a Wide‐range Particle Spectrometer (WPS). Size‐segregated aerosol samples were collected concurrently using a Micro‐Orifice Uniform Deposit Impactor (MOUDI), which aided our in‐depth understanding of the new particle formation (NPF) mechanism in the polluted Yangtze River Delta area. During the observations, 16 NPF events occurred at high temperatures (~34.7°C) on clear and sunny days. In the ammonium‐poor PM1.0 (particulate matter less than 1.0 µm), sulfate and ammonium accounted for 92% of the total water‐soluble inorganic species. Six aminiums were detected in these MOUDI samples, among which the group of diethylaminium and trimethylaminium (DEAH+ + TMAH+) was the most abundant. The very high level of aminiums (average concentration up to 86.4 ng m−3 in PM1.8), together with highly acidic aerosols, provided insight into the frequent NPF events. The high mass ratio of total aminiums to NH4+ (&gt;0.2 for PM0.056) further highlighted the important role of amines in promoting NPF. The concentration of DEAH+ + TMAH+ in new particles below 180 nm was strongly correlated with aerosol phase acidity, indicating that acid‐base reactions dominated the aminium formation in NPF events. The unexpected enhancement of DEAH+ + TMAH+ on a nonevent day was attributed to the transportation of an SO2 plume. Our results reveal that the heterogeneous uptake of amines is dominated by the acid‐base reaction mechanism, which can effectively contribute to particle growth in NPF events.

Using Lidar, in-situ measurements and Trajectory Analysis to observe air pollution in Beijing, 2014

We present combined Mie lidar, ozone lidar and wide-range particle spectrometer observations that were carried out in Beijing, north China during two periods—one haze period before the Asia-Pacific Economic Cooperation (APEC) meeting and one moderate pollution period during the meeting in 2014. High extinction coefficient, moderate ozone concentration and variable particle number concentration were obtained throughout the first haze observation period. The mean extinction coefficients in the two pollution periods were 0.52 km-1 and 0.23 km -1 , respectively, at 532 nm. The ozone concentration during the first haze phase was more various with higher average value of 49 ppb compared to that in the second pollution observations (32 ppb). The comparison of aerosols and ozone in different heights indicate different pollution sources and complicated ozone process of generation and disappearance. The four-day back trajectories from a HYSPLIT model indicate that the air masses in the lower boundary layer were advected from the densely populated south regions of China and the long pollution transportation passing through northern China.

Haze observations by simultaneous lidar and WPS in Beijing before and during APEC, 2014

We present combined Mie lidar, ozone lidar and wide-range particle spectrometer observations which were carried out in Beijing, north China during two periods—one haze period before the Asia-Pacific Economic Cooperation (APEC) meeting and one moderate pollution period during the meeting in 2014. High extinction coefficient, moderate ozone concentration and variable particle number concentration were obtained throughout the first haze observation period. The mean extinction coefficients in the two pollution periods were 0.52 and 0.23 km-1, respectively, at 532 nm. The ozone concentration during the first haze phase was more various with a higher average value of 49 ppb compared with that in the second pollution observations (32 ppb). Compared with the same metrological condition occurring at the end of October, the sharply decreased aerosol extinction coefficient and ozone concentration show the effectiveness of the emission-cutting measures implemented during APEC in November. The comparison of aerosols and ozone in different heights indicate different pollution sources and the complicated ozone process of generation and disappearance. The correlation between the scattering coefficient and particle number concentrations of various diameter depended on the ambient humidity. Especially the particle number concentration (500 nm–1 µm) contributed most to PM2.5 concentration. The four-day back trajectories from a Hybrid Single-particle Lagrangian Integrated Trajectory (HYSPLIT) model indicate that the air masses in the lower boundary layer before and during APEC were advected from the densely populated south regions of China and the long pollution transportation passing through northern China.

Evaluation of the particle infiltration efficiency of three passive samplers and the PS-1 active air sampler

The particle infiltration efficiencies (PIE) of three passive and one active air samplers were evaluated under field conditions. A wide-range particle spectrometer operating in the 250–4140 nm range was used to acquire highly temporally resolved particle-number and size distributions for the different samplers compared to ambient air. Overall, three of the four evaluated samplers were able to acquire a representative sample of ambient particles with PIEs of 91.5 ± 13.7% for the GAPS Network sampler, 103 ± 15.5% for the Lancaster University sampler, and 89.6 ± 13.4% for a conventional PS-1 high-volume active air sampler (Hi-Vol). Significantly (p = 0.05) lower PIE of 54 ± 8.0% was acquired for the passive sampler used under the MONET program. These findings inform the comparability and use of passive and active samplers for measuring particle-associated priority chemicals in air.

Synthesis of hybrid carbon nanotube structures coated with Sophora flavescens nanoparticles and their application to antimicrobial air filtration

Controlling airborne microorganisms has become increasingly important with increase in human indoor activities, epidemic disease outbreaks, and airborne pathogen transmission. Treatments using antimicrobial nanoparticles have shown promise because of the high surface-to-volume ratio of nanoparticles compared to their bulk counterparts, and their unique physical and chemical properties. In this study, hybrid nanostructures of multi-walled carbon nanotubes (MWCNTs) coated with antimicrobial, natural product (NP) nanoparticles were synthesized using a twin-head electrospray system (THES). The coated nanoparticles were then used in antimicrobial air filters to increase their antimicrobial efficiency. Electrosprayed droplets were converted to NP nanoparticles and MWCNTs through ethanol evaporation. Oppositely charged NP nanoparticles and MWCNTs were coagulated via Coulombic collisions to form hybrid nanoparticles that were deposited continuously onto an air filter medium. The size distribution and composition of the hybrid NP/MWCNT particles were characterized using a wide-range particle spectrometer (WPS) and transmission electron microscope (TEM). The concentration of hybrid NP/MWCNT nanoparticles was lower than that of NP nanoparticles but higher than that of MWCNTs and showed a bimodal size distribution with peak diameters of 21.1 and 49nm. TEM analyses confirmed that the NP nanoparticles were attached to the MWCNT surface with a density of ~4–9 particles/MWCNT. When deposited onto the filter medium, NP/MWCNT particles formed dendrites on the filter׳s fiber surface. The filtration efficiency and pressure drop of the NP/MWCNT-coated filters were higher than those of pristine, NP nanoparticles-coated or MWCNTs-coated filters. The hybrid filter also exhibited stronger antimicrobial activity than those of NP or MWCNT-coated filters at identical deposited volumes (1.1×10–2cm3/cm2filter). Ninety-five percent of the tested bacterial aerosols were inactivated on the NP/MWCNTs filter while only <70% were inactivated on NP- or MWCNT-coated filters.

Characteristics of new particle formation events in Nanjing, China: Effect of water-soluble ions

New particle formation (NPF) events and water-soluble ions were studied at the meteorological building on the campus of the Nanjing University of Information Science and Technology (NUIST), which is located in the western part of the Yangtze River Delta (YRD). A wide-range particle spectrometer (WPS) provided particle number size distributions between 10 nm and 10 μm, whereas water-soluble ions for particles with diameters between 10 nm and 18 μm were measured using a 13-stage Nano-MOUDI aerosol sampler and 850 professional Ion Chromatography (IC). Additionally, meteorological data, trace gas concentrations and mass concentration were recorded. Ten NPF days were captured during the measurement period from 08 July to 02 August 2012. The mean aerosol number concentration, which was primarily composed of Aitken-mode particles, i.e., with diameters of 20–100 nm, was 13,664 cm−3, which was 1.9 times larger than that on non-NPF days. The results suggest that the NPF events were only slightly affected by O3, SO2, and NO2; the primary factors affecting NPF events were meteorological factors and air mass directions. NPF events were found to be favorable during the summer in the presence of high temperatures, strong radiation, low humidity, strong winds and clean air masses originating from the southeastern coast. The mean growth rate (GR), formation rate (J10), condensational sink (CS), condensing vapor rate (Q), and condensation vapor (C) were determined to be 7.6 nm h−1, 3.7 cm−3 s−1, 2.8 × 10−2 s−1, 2.9 × 106 cm−3 s−1, and 10.5 × 107 cm−3, respectively, on NPF days. The largest effects of the studied NPF events were on the mass and water-soluble ion concentrations of Aitken-mode particles, followed by nuclei-mode particles; few contributions to accumulation- and coarse-mode particles were observed. Different water-soluble ions were observed to have distinct interactions with the NPF events. The proportions of NH4+, SO42−, NO3−, K+ and Mg2+ in nuclei- and Aitken-mode particles to the total concentrations on NPF days were substantially higher than on non-NPF days.

Integrated evaluation of aerosols during haze-fog episodes at one regional background site in North China Plain

To investigate haze-fog (HF) formation mechanisms and transport, trace gases and aerosols in the aged air masses during regional haze episodes were measured at a regional background site in the North China Plain during 4–19 July, 2011. Mixing state of individual particles, soluble ions of PM2.5, and particle number concentrations were studied using transmission electron microscope, ambient ion monitoring, and wide-range particle spectrometer, respectively. Average mass concentration of PM2.5 was 3 times higher on HF days (70μg/m3) than on clear days (22μg/m3). The major soluble ionic components (SO42−, NO3−, and NH4+) in PM2.5 were over 4 times higher on HF days (40.6μg/m3) than on clear days (9.1μg/m3). The high sulfur oxidation ratios (SOR) and nitrogen oxidation ratios (NOR) values during HF days suggest that polluted weather favored transformation of SO2 and NOx into sulfates and nitrates compared to clear days. Particle number fraction of the accumulation mode increases from 11% on clear days up to 26% on HF days. Individual particle analysis shows that secondary inorganic particles (e.g., sulfate and nitrate) as the most abundant species likely determine internal mixing of individual particles and almost half of them mixed refractory particles (e.g., metal, fly ash, soot, and mineral) on HF days. These fine refractory particles were likely emitted from coal fired power plants, heavy industries, and urban city in Shandong and Hebei provinces. Our results suggest that aged air masses mostly contain aged particles of long-range transport and some from new particle formation and growth in the regional background atmosphere.

Number size distribution of aerosols at Mt. Huang and Nanjing in the Yangtze River Delta, China: Effects of air masses and characteristics of new particle formation

Aerosol number spectra in the range of 10nm–10μm were observed at Mt. Huang (Aug. 15–Sep. 15) and Nanjing (Oct. 13–Nov. 15) by a wide-range particle spectrometer (WPS) in 2011. Based on the backward trajectories obtained using the HYSPLIT model, the transport pathways of observed air masses during the study periods were classified into the following four groups: maritime air mass, continental air mass, marine–continental mixed air mass and local air mass. The variations in the aerosol number spectrum and the new particle formation (NPF) events for various types of air masses were discussed, along with meteorological data. The results showed that the average number concentration was 12,540cm−3 at Nanjing and only 2791cm−3 at Mt. Huang. The aerosol number concentration in Nanjing was 3–7 times higher than that in Mt. Huang; the large discrepancy was in the range of 10–100nm. Different types of air masses had different effects on number concentration distribution. The number concentration of aerosols was higher in marine air masses, continental air masses and continental–marine mixed air masses at 10–50nm, 100–500nm and 50–200nm, respectively. Under the four types of air masses, the aerosol size spectra had bimodal distributions in Nanjing and unimodal distributions in Mt. Huang (except under continental air masses: HT1). The effects of the diverse air masses on aerosol size segments of the concentration peak in Mt. Huang were stronger than those in Nanjing. The local air masses were dominant at these two sites and accounted for 44% of the total air masses. However, the aerosol number concentration was the lowest in Mt. Huang and the highest in Nanjing when local air masses were present. The number concentrations for foreign air masses increased at Mt. Huang and decreased at Nanjing. Different types of air masses had greater effects on the aerosol spectrum distribution at Mt. Huang than at Nanjing. During the NPF events, the particle growth rates at Mt. Huang (6.5–9.0nmh−1) were faster than those at Nanjing (4.8–5.6nmh−1). The relative humidity at Mt. Huang (36–65%) was higher than that at Nanjing (30–47%), but the wind speed trend was the opposite. The air masses during the NPF events were clean, i.e., they were mainly from over the ocean or districts with low ultrafine particle concentrations.