Total Particle Number Concentration Research Articles

Experimental and numerical study on the effect of single-hydroxybenzene/n-heptane blends on engine combustion and particulate emissions

Understanding the influence of the primary components of diesel on engine combustion and emissions is essential to the construction of a model diesel fuel. In this study, straight-chain alkanes in diesel are represented by n-heptane, and aromatic hydrocarbons are represented by toluene, n-butylbenzene, and 1,2,4-trimethylbenzene. The effect of single-hydroxybenzene/n-heptane blended fuel on engine performance and particle emission characteristics is studied experimentally and by simulation to identify an optimal composition for a model diesel fuel. The test fuels were pure diesel (D100) and single-hydroxybenzene/n-heptane blends (toluene, n-butylbenzene and 1,2,4-trimethylbenzene each of which was added to n-heptane at a volume ratio of 20% (T20, BBZ20, TMB20) or 30% (T30, BBZ30, TMB30)). The results show that as the EGR rate increases, the total particle number concentration (TPNC), particle size distribution concentration (PSDC), total particle mass concentration (TPMC), and particle geometric mean diameter (PGMD) increase. The peak heat release rate (HRR) and peak in-cylinder pressure (IP) of single-hydroxybenzene/n-heptane are higher than those of D100; however, the values of PSDC, TPNC, TPMC, and PGMD are lower than those of D100. Among the tested fuels, the effects of n-butylbenzene/n-heptane blend on engine performance and particle emission characteristics are closest to D100. The spatial distribution of temperature field, equivalent ratio, OH-groups and NO of BBZ20 are close to that of D100. The n-butylbenzene/n-heptane fuel is suitable for modeling diesel, particularly when the addition ratio of n-butylbenzene is 20%, the combustion and emission characteristics are the closest to those of D100.

Students exposure assessment towards PM number concentration while commuting from different transport modes during school timings

Among the various daily activities, commuting to school is considered as an important activity for the students. While commute, students are exposed to elevated particle concentrations that make significant contributions to their daily personal exposures. Present study compares the student exposure towards particle number concentration (PNC) and inhaled doses while commuting from different transports during morning (MT) and afternoon (AT) trips. PNC was measured from four different transport modes: two-wheeler (2W), three-wheeler (3W), passenger car (PC) and school bus (SB) during summer and winter seasons. In summer season, average total PNC was highest for 3W and SB during MT (5.53E+07 # m−3) and AT (5.29E+07 # m−3) trips respectively. However, in winter season, 3W has the highest average total PNC during MT (1.04E+08 # m−3) and AT (7.92E+07 # m−3) trips. Ventilation settings greatly influence the in-cabin PNC and found to be highest under window open (WO) scenario for PC and least under WO and window closed scenarios for SB during MT and AT trips respectively. The PNC exposure varies significantly with student seating positions inside SB and followed different trends during MT (front > middle > rear) and AT (rear > front > middle) trips. The mixed-effect multivariate linear regression model was used to estimate the effects of multiple predictor variables that influence the PNC measured from different transport modes while commuting. Background concentration (PNC) and meteorological variables (wind speed, ambient temperature and relative humidity) were important predictors of PNC measured while commuting and explained the variability between 0.04–27.31%.

Effects of PODE/diesel blends on particulate matter emission and particle oxidation characteristics of a common-rail diesel engine

The current study focused on the particulate matter emissions of polyoxymethylene dimethyl ethers (PODE)/diesel blends with PODE blending ratios of 0, 10%, 20% and 30% have been experimentally investigated in a common-rail engine. The influences of PODE blending ratio on the smoke emission, particle size distribution and particle oxidation characteristic are discussed. Results show that the addition of PODE in diesel fuel can effectively reduce smoke emission and its decreasing range becomes larger with increasing PODE blending ratio. With the increment in PODE blending ratio, the particle concentration distribution moves towards the direction of small particle size, and the total particle number concentrations decrease. Besides, the peak values of particle number concentration, surface area concentration, and volume concentration are all decreased. Adding PODE in diesel fuel increases the soluble organic fraction (SOF) content of particles, rises maximum weight loss rate of particles, and lower the peak temperature of particles. Also, the activation energy of pyrolysis reaction of particles decreases, which indicates that the oxidation of particles becomes easier as PODE blending ratio increases. The apparent morphology of particles was measured by scanning electron microscope, and the results show that the morphology of particles sample are mostly chain like or flocculent.

Effect of dimethoxymethane (DMM) additive on combustion and emission characteristics under different working conditions in CI engines

Dimethoxymethane (DMM) is considered a potential oxygenated fuel due to its high oxygen content (42.1%) and considerable heat value. However, little research emphasizes the impact of oxygenated fuels on small-particles (DP < 25 nm), which is harmful for human beings. In this investigation, the effect of DMM-diesel mixture on combustion and emission characteristics of a four-cylinder commercial CI engine is studied under normal working speeds and loads. Especially, the influence of DMM-diesel fuels on PMs included small-particles is analyzed comprehensively. The results show that the brake thermal efficiency (BTE) of DMM13 and DMM6.4 fuels increases by 1.06% and 0.4%, respectively, compared with that of D100 at the condition of 1400 rpm and 1.0 MPa. In terms of emission, the soot emission of DMM13 is reduced by 46% with respect to that of D100 at the condition of 0.6 MPa and 1400 rpm. Meanwhile, with the addition of DMM13, the peak particle number concentration (PNC) drops significantly, but increasing the proportion of small-particles. Moreover, the lowest total particle mass concentration (TPMC) is obtained as well. Substantially, DMM-diesel blends can realize the balance between low total particle number concentration (TPNC) and small geometric mean diameter (GMD).

Trends in primary and secondary particle number concentrations in urban and regional environments in NE Spain

We analysed long-term datasets of ambient air concentrations of gaseous pollutants, black carbon (BC) and particle size distributions at an urban background air quality station (Barcelona, Spain; 2013–2019) and a regional background station (Montseny, Spain; 2014–2019). Using BC as a tracer of primary emissions, we segregated the aerosol load in modes and analysed their trends, considering all-year data and seasons separately. We also applied the positive matrix factorisation (PMF) receptor model to the particle size distributions to identify different sources that contribute to the particle number concentration. Our results show that the number concentration of primary particles decreased at the urban and regional background stations (−4.1 and −4.7% per year, respectively) along the period of study. This decrease was also observed for primary particles in the nucleation, Aitken and accumulation modes separately. This change leads to a decrease in condensation sinks (CS, −3.1 and −5.6% per year), that, together with an increase in temperatures (+1.5% per year in the urban background; +1.4% per year in the regional background), results in a markedly increasing trend in the contribution of new particle formation to the total number particle concentration (+17.7% and +11.9% per year). The total particle number concentration decreased in the urban background (−2.5% per year), whereas the trend increased for the regional background (+3.0% per year). The latter result is in contrast to most literature reports and is most likely due to higher insolation and increased biogenic VOC (BVOC) emissions that would enhance photonucleation, along with a marked decrease in the CS. An increasing trend in H2SO4 concentrations driven by increasing SO2 concentrations (+11.1% per year) could also be favouring the formation of new particles in the regional background, but it is not clear that the increasing trend in SO2 is real or it is related to a faulty maintenance of the instrumentation.Overall, we conclude that decreasing primary emissions results in a decrease in the total number concentrations of urban aerosols, despite the increase in the formation of new particles by photonucleation. Moreover, the total particle number concentration of regions downwind of the urban areas increases because new particle formation is more favoured and compensates for the primary particles’ number concentration decrease.

Horizontal injection spray drying aerosol generator using an ultrasonic nozzle with clean counter flow

We investigated a spray-drying aerosol generator that can generate micro-particles at high concentration using an ultrasonic nozzle. Unlike a conventional spray-drying aerosol generator that uses vertical spray with co-current sheath flow, we designed a new aerosol generator by using horizontal spray with co-current sheath flow combined with clean counter flow to increase particle generation efficiency. A drying chamber was designed using the ANSYS Fluent solver to complete the evaporation of droplets and to minimize the loss of post-evaporation particles inside the chamber. Both numerical prediction and experimental data showed that droplets would completely evaporate at a temperature of 353 K. Both KCl aqueous solution and silica powder suspension were sprayed using an ultrasonic nozzle to generate micro-sized particles with a size range of 1–10 μm. When horizontal spray with co-current sheath flow was operated with clean counter flow the loss of particles on the chamber wall was minimized and thus the total particle number concentration was 2.4 times higher than when the clean counter flow was inactive. The particle generator in the present study can generate larger particles than a Collison atomizer which generates particles up to 3 μm.

Influence of fuel injection pressure and injection timing on nanoparticle emission in light-duty gasoline/diesel RCCI engine

This work investigates the influence of fuel injection events on the nanoparticle emission characteristics of light-duty gasoline-diesel RCCI engine. The formation of nanoparticle emissions strongly depends on fuel injection events. The present study experimentally investigates the influence of diesel injection pressure, injection timing, and port-injected gasoline mass on the nanoparticles emitted from the gasoline-diesel RCCI engine. For this purpose, the engine is tested at different engine speeds and a fixed load of 1.5 bar BMEP without exhaust gas recirculation. The particle-size and number distribution (PSD) and total particle number (total PN) concentration are measured using a differential mobility spectrometer. The results depict that at higher diesel injection pressure (IP) operation, the peak of the NMP increases while the AMP peak decreases for neat diesel operation as well as RCCI engine. Nucleation, as well as accumulation mode particles, increases with advanced diesel injection timing in RCCI combustion. An increase in port fuel injected mass also leads to an increase in the total particle concentration and total unburned hydrocarbon (THC) emissions.

Discoveries in Aerosol Science: Characterization of Nanoparticles Emitted From Metallic Coils in Electronic Cigarettes

Electronic (e-) cigarettes, also known as electronic nicotine delivery systems, are battery-operated devices that are growing in popularity worldwide. Although e-cigarettes are known to be safer than traditional cigarettes, their potential health risks have not been extensively reviewed yet. In this study, aerosol nanoparticles generated from e-cigarette heaters were characterized. Kanthal A1 (iron + chromium + aluminum) coils, without nicotine solution or a wick, were installed in an e-cigarette atomizer. The operating conditions were varied coil resistances (0.1–1.0 Ω), a set applied power (10 W), and a stable duty cycle (50%: 5 s on, 5 s off ). The size distribution and morphology of particles were collected by a scanning mobility particle sizer and evaluated by transmission electron microscopy, respectively. From an applied power of 10 W and a 50% duty cycle, the size and total number concentration (TNC) of particles emitted increased with greater coil resistances. Within these operating conditions, the average TNC of particles generated exhibited a steep decrease during the first 15 minutes of each trial. The TNC of particles decreased over time because surface oxidation (iron oxide layer) prevented further nanoparticle emission. As a result, a used coil may reduce the risk of the metal exposure from e-cigarettes. The results indicate that our designed and tested e-cigarette generation system is useful for future research that aims to investigate the health impacts of metallic particle inhalation on e-cigarette users.

Ultrafine aerosol particles in the western Caribbean: A first case study in Merida

Aerosol particles have been shown to trigger cardiovascular and respiratory diseases in populations living in polluted regions, depending on their size and composition. Although fine aerosol particles have been found to reach the lungs and the blood stream, their acute effects are related to the fraction of ultrafine aerosol particles (i.e., UFPs, d < 0.1 μm). In the present study, the concentration of UFPs (d = 0.02–0.1 μm) was monitored in Merida (Yucatan) between April 2017 and July 2018. Additionally, the total aerosol particle concentration (d > 0.03 μm), PM10, PM2.5, criteria gases, and meteorological variables, were also monitored. The average UFPs concentration over the full sampling period was found to be 2,070 ± 1,831 cm-3, with events of peak concentrations as high as 55,117 cm−3. The average daily UFP profile is bimodal, with peak concentrations observed around 07:00 and 20:00 h LT. The correlation of the UFP with other measured variables suggests that the UFPs peaks observed in the morning and at night are likely caused by primary vehicular combustion particles. In contrast, atypical high concentrations of UFPs were occasionally observed around noon LT, which are likely of secondary origin and the result of new particle formation promoted by photochemistry. Overall, UFPs are the major contributor to the total particle number concentration, and they are likely an important contributor to PM2.5 in Merida during the morning hours, with clear anthropogenic sources.

Global Alliance against Chronic Respiratory Diseases demonstration project: aerosol pollution and its seasonal peculiarities in primary schools of Vilnius.

BackgroundThe growing public health concern caused by non-communicable diseases in urban surroundings cannot be solved by health care alone; therefore a multidisciplinary approach is mandatory. This study aimed to evaluate the airborne aerosol pollution level in primary schools as possible factor influencing origin and course of the diseases in children.MethodsSeasonal aerosol particle number concentration (PNC) and mass concentration (PMC) were studied in the randomly selected eleven primary schools in the Lithuanian capital, Vilnius, as model of a middle-size Eastern European city. Total PNC in the size range from 0.01 to >1.0 μm in diameter was measured using a condensation particle counter. Using an optical particle sizer, PNC was measured and PMC estimated for particles from 0.3 to 10.0 μm. A descriptive statistics was used to estimate the aerosol pollution levels.ResultsDuring all seasons, local cafeterias in the absence of ventilation were the main sources of the elevated levels of indoor PMC and PNC (up to 97,500 particles/cm3). The other sources of airborne particulates were the children's activity during the lesson breaks with PMC up to 586 μg/m3. Soft furniture, carpets in the classrooms and corridors were responsible for PMC up to 200 μg/m3. Outdoor aerosol pollution (up to 18,170 particles/cm3) was higher for schools in city center. Elevated air pollution in classrooms also resulted from intermittent sources, such as construction work during classes (200–1000 μg/m3) and petrol-powered lawn trimmers (up to 66,400 particles/cm3).ConclusionThe results of our survey show that even in a relatively low polluted region of Eastern Europe there are big differences in aerosol pollution within middle-sized city. Additional efforts are needed to improve air quality in schools: more frequent wet cleaning, monitoring the operation of ventilation systems, a ban on construction works during school year, on a use of sandblasting mechanisms in the neighborhood of schools.

Composite In Situ Microphysical Analysis of All Spiral Vertical Profiles Executed within BAMEX and PECAN Mesoscale Convective Systems

AbstractVertical profiles of temperature, relative humidity, cloud particle concentration, median mass dimension, and mass content were derived using instruments on the NOAA P-3 aircraft for 37 spiral ascents/descents flown within five mesoscale convective systems (MCSs) during the 2015 Plains Elevated Convection at Night (PECAN) project, and 16 spiral descents of the NOAA P-3 within 10 MCSs during the 2003 Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). The statistical distribution of thermodynamic and microphysical properties within these spirals is presented in context of three primary MCS regions—the transition zone (TZ), enhanced stratiform rain region (ESR), and the anvil region (AR)—allowing deductions concerning the relative importance and nature of microphysical processes in each region. Aggregation was ubiquitous across all MCS zones at subfreezing temperatures, where the degree of ambient subsaturation, if present, moderated the effectiveness of this process via sublimation. The predominately ice-supersaturated ESR experienced the least impact of sublimation on microphysical characteristics relative to the TZ and AR. Aggregation was most limited by sublimation in the ice-subsaturated AR, where total particle number and mass concentrations decreased most rapidly with increasing temperature. Sublimation cooling at the surface of ice particles in the TZ, the driest of the three regions, allowed ice to survive to temperatures as high as +6.8°C. Two spirals executed behind a frontal squall line exhibited a high incidence of pristine ice crystals, and notably different characteristics from most other spirals. Gradual meso- to synoptic-scale ascent in this region likely contributed to the observed differences.

The influence of school bus ventilation scenarios over in-cabin PM number concentration and air exchange rates

School students are exposed to the increased particulate (PM) number concentration inside the school bus on daily basis while commuting on urban road networks. However, the potential effect of different ventilation over in-cabin pollutants is still unclear in many aspects. The present paper investigates the influence of varying ventilation scenarios over in-cabin particle number concentration (PNC) and air exchange rates (AERs) inside idle and moving (unoccupied (SBu) and occupied (SBo)) school bus. The in-cabin total PNC sharply increased by a factor of 1.53, 1.57 and 1.14 for SBp, SBu, and SBo respectively under windows open (WO) from windows closed (WC) scenarios. In-vehicle student activity and ventilation scenarios were positively correlated with the change in in-cabin PNC. For SBp, the average estimated AERs are 9.19 h−1 and 3.30 h−1 under WO and WC scenarios respectively whereas, total PNC deposition rate under natural convection condition varied between 2.52 to 6.89 h−1. In the present study, inside-outside measurements were recorded for 10 km long road segment under realistic driving conditions. The average AERs value of SBu and SBo are highest for WO (42.40 h−1 and 14.46 h−1) compared to WC (10.91 h−1 and 10.94 h−1) scenarios. A Generalized estimating model (GEE) model was developed and the model suggested that vehicle age, mileage, and speed are the factors positively associated with the AERs estimated for WO and WC scenarios under realistic driving conditions.

Atmospheric aerosol properties at a semi-rural location in southern India: particle size distributions and implications for cloud droplet formation

Particle number size distributions in the diameter range of 5 nm–34 µm were measured in tropical southern India during the transition season from May (pre-monsoon) to June–July (monsoon). Averaged over the entire measurement period, the particle number size distributions were bimodal with a total particle number concentration of NTot = (4.5 ± 2.7) × 103 cm−3 (arithmetic mean ± standard deviation). The ratio of Aitken to accumulation mode particle number concentrations (NAit/NAcc) ranged from 1.06 to 2.07, increasing from May to June–July due to a pronounced decrease in the accumulation mode particles with the onset of the monsoon. Cloud condensation nuclei concentrations at 0.4% supersaturation (CCN0.4) were calculated under the assumption of an average continental hygroscopicity parameter of κ = 0.3. The calculated CCN0.4 concentrations are mostly sensitive to variations in NAcc and vary accordingly between the May and June–July. Using a cloud parcel model, we investigated the formation of cloud droplets using the measured average particle number size distributions, updraft velocities up to 20 m s−1, and initial aerosol particle number concentrations up to 25,000 cm−3. We found different regimes of CCN activation and cloud formation for the month of May (shifting from aerosol-limited regime to transitional regime) and for June–July (transitional regime), which was primarily due to the variability of particle number concentrations in the accumulation mode.

Ultrafine Particle Features Associated with Pro-Inflammatory and Oxidative Responses: Implications for Health Studies

Suspected detrimental health effects associated with ultrafine particles (UFPs) are impressive. However, epidemiological evidence is still limited. This is potentially due to challenges related to UFP exposure assessment and the lack of consensus on a standard methodology for UFPs. It is imperative to focus future health studies on those UFP metrics more likely to represent health effects. This is the purpose of this paper, where we extend the results obtained during the CARE (“Carbonaceous Aerosol in Rome and Environs”) experiment started in 2017 in Rome. The major purpose is to investigate features of airborne UFPs associated with pro-inflammatory and oxidative responses. Aerosol chemical, microphysical, and optical properties were measured, together with the oxidative potential, at temporal scales relevant for UFPs (minutes to hours). The biological responses were obtained using both in-vivo and in-vitro tests carried out directly under environmental conditions. Findings indicate that caution should be taken when assessing health-relevant exposure to UFPs through the conventional metrics like total particle number concentration and PM2.5 and Black Carbon (BC) mass concentration. Conversely, we recommend adding to these, a UFP source apportionment analysis and indicators for both ultrafine black carbon and the size of particles providing most of the total surface area to available toxic molecules.

Effect of alcohols on combustion characteristics and particle size distribution of a diesel engine fueled with diesel‐castor oil blended fuel

AbstractThe research was motivated to experimentally study the effect of alcohol addition on the performance, combustion characteristics, particle size distribution (PSD) and exhaust emissions of a common rail direct injection (CRDI) diesel engine fueled with diesel‐castor oil blended fuels. The main properties of the blended fuels were measured by the standard test procedures. The results revealed that, compared with diesel fuel, the brake specific fuel consumption (BSFC) was increased by an average of 7.7%, 8.5% and 16.5% for DA80B10E10, DC80B20, and DC60B20E20 fuels respectively. The brake thermal efficiency (BTE) kept almost identical for the blended fuels. The peak in‐cylinder pressure was about 0.4 MPa higher and the heat release rate (HRR) was evidently higher than that of diesel fuel, and the combustion duration was 5–12 crank angles shorter. The blended fuels exhibited bi‐modal PSD, and diesel fuel showed uni‐modal behavior under all operating conditions. The total number concentration (TNC) of particles was larger, but the geometric mean diameter (GMD) was lower than that of diesel fuel. Nitrogen oxide (NOx) emissions were increased by about 30% and hydrocarbon (HC) was evidently higher for the blended fuels under almost all operating conditions, but carbon monoxide (CO) emissions were about 22% lower than that of diesel fuel.

Long-Term Characterization of Submicron Atmospheric Particles in an Urban Background Site in Southern Italy

Continuous measurements of particle number size distributions in the size range from 10 nm to 800 nm were performed from 2015 to 2019 at the ECO Environmental-Climate Observatory of Lecce (Global Atmosphere Watch Programme/Aerosol, Clouds and Trace Gases Research Infrastructure (GAW/ACTRIS) regional station). The main objectives of this work were to investigate the daily, weekly and seasonal trends of particle number concentrations and their dependence on meteorological parameters gathering information on potential sources. The highest total number concentrations were observed during autumn-winter with average values nearly twice as high as in summer. More than 52% of total particle number concentration consisted of Aitken mode (20 nm &lt; particle diameter (Dp) &lt; 100 nm) particles followed by accumulation (100 nm &lt; Dp &lt; 800 nm) and nucleation (10 nm &lt; Dp &lt; 20 nm) modes representing, respectively, 27% and 21% of particles. The total number concentration was usually significantly higher during workdays than during weekends/holidays in all years, showing a trend likely correlated with local traffic activities. The number concentration of each particle mode showed a characteristic daily variation that was different in cold and warm seasons. The highest concentrations of the Aitken and accumulation particle mode were observed in the morning and the late evening, during typical rush hour traffic times, highlighting that the two-particle size ranges are related, although there was significant variation in the number concentrations. The peak in the number concentrations of the nucleation mode observed in the midday of spring and summer can be attributed to the intensive formation of new particles from gaseous precursors. Based on Pearson coefficients between particle number concentrations and meteorological parameters, temperature, and wind speed had significant negative relationships with the Aitken and accumulation particle number concentrations, whereas relative humidity was positively correlated. No significant correlations were found for the nucleation particle number concentrations.

An analytical solution of the population balance equation for simultaneous Brownian and shear coagulation in the continuum regime

Brownian coagulation of aerosol particles can take place in both laminar and turbulent flows. Thus, the simultaneous Brownian and shear coagulation will always occur in practical applications. This study presents an analytical solution to describe the size evolution of polydisperse particles undergoing simultaneous Brownian and shear coagulation. The analytical solution is derived using the log-normal method of moments (LNMOM) with some approximations. Then, the analytical solution is validated by comparing with previous analytical solutions derived for limiting cases. The results show that the present analytical solution is consistent with previous analytical solutions for these limiting cases. Further, the time trajectories of the total particle number concentration, the geometric standard deviation and the geometric number mean particle volume predicted by the present analytical solution are compared with those of a numerical LNMOM model. The results show that the present analytical solution gives good predictions of the total particle number concentration but less accurate predictions of the geometric standard deviation and the geometric number mean particle volume. A dimensionless analysis shows that the coagulation rate ratio and the initial polydispersity are two important factors for characterizing the size evolution of simultaneous Brownian and shear coagulation.

Wind Effect on the Size Distribution of Saltating Particles

Size distributions of saltating aleurite and sand particles have been measured in a windsand flux in a desertified area in Astrakhan oblast. The distributions are approximated by a sum of lognormal distributions for the aleurite-sand and aleurite fractions. The threshold wind velocity for the total particle concentration is determined under conditions of nonintermittent saltation. It is found that the threshold velocity depends on the size of saltating particles. Empirical approximations of the total number concentration and differential particle concentration of aleurite and sand particles as functions of wind velocity are obtained.

Real time detection and characterisation of bioaerosol emissions from wastewater treatment plants

Bioaerosol emissions from wastewater treatment plants may pose adverse health impact on workers and nearby communities. To detect and characterise bioaerosol emissions from wastewater treatment plant (WWTP), a novel real-time bioaerosol sensor, Spectral Intensity Bioaerosol Sensor (SIBS) was employed at a WWTP and a background site. The SIBS records a range of data (size, shape, and fluorescence emission across 16 wavelength bands from 298 to 735 nm for two excitation wavelengths (285 nm and 370 nm)) on single particles in real time. Additionally, excitation-emission matrix (EEM) of wastewater samples obtained by a spectrofluorometer was compared with SIBS spectra from WWTP. The results showed that the average number concentrations of total particles (NT) and fluorescence particles (NF) were both higher at the WWTP (NT = 2.01 cm−3, NF = 1.13 cm−3) than the background site (NT = 1.79 cm−3, NF = 1.01 cm−3). The temporal variation of NF and NT was highly variable at the WWTP and the concentration peaks were consistent with on-site activities. Moreover, the time-resolved number-size distribution of fluorescent particles revealed the predominance of fine scale particles (<1 μm) and the time-series channel by channel number concentrations demonstrated the temporal variability of dominant bio-fluorophores. Furthermore, the overall and size-segregated fluorescence spectra at two sites were multimodal. In particular, the fluorescence intensity increases with increasing particle size in WWTP spectra, which is not present in the background spectra. In addition, the highly resolved SIBS fluorescence spectra were broadly similar to EEM of wastewater. These findings confirmed that the spectrally resolved fluorescence detected by SIBS is capable of providing reliable bio-fluorophores information of bioaerosol emissions generated from wastewater, thus holding the potential for better characterisation of bioaerosols in real time.

Characterization of aerosol particles at Cabo Verde close to sea level and at the cloud level – Part 1: Particle number size distribution, cloud condensation nuclei and their origins

Abstract. In the framework of the MarParCloud (Marine biological production, organic aerosol particles and marine clouds: a Process Chain) project, measurements were carried out on the islands of Cabo Verde (a.k.a. Cape Verde) to investigate the abundance, properties and sources of aerosol particles in general, and cloud condensation nuclei (CCN) in particular, both close to sea level and at the cloud level. A thorough comparison of particle number concentration (PNC), particle number size distribution (PNSD) and CCN number concentration (NCCN) at the Cape Verde Atmospheric Observatory (CVAO, sea-level station) and Monte Verde (MV, cloud-level station) reveals that during times without clouds the aerosols at CVAO and MV are similar and the boundary layer is generally well mixed. Therefore, data obtained at CVAO can be used to describe the aerosol particles at cloud level. Cloud events were observed at MV during roughly 58 % of the time, and during these events a large fraction of particles was activated to cloud droplets. A trimodal parameterization method was deployed to characterize PNC at CVAO. Based on number concentrations in different aerosol modes, four well-separable types of PNSDs were found, which were named the marine type, mixture type, dust type1 and dust type2. Aerosol particles differ depending on their origins. When the air masses came from the Atlantic Ocean, sea spray can be assumed to be one source for particles besides new particle formation. For these air masses, PNSDs featured the lowest number concentration in Aitken, accumulation and coarse modes. Particle number concentrations for sea spray aerosol (SSA, i.e., the coarse mode for these air masses) accounted for about 3.7 % of NCCN,0.30 % (CCN number concentration at 0.30 % supersaturation) and about 1.1 % to 4.4 % of Ntotal (total particle number concentration). When the air masses came from the Sahara, we observed enhanced Aitken, accumulation and coarse mode particle number concentrations and overall increased NCCN; NCCN,0.30 % during the strongest observed dust periods is about 2.5 times higher than that during marine periods. However, the particle hygroscopicity parameter κ for these two most different periods shows no significant difference and is generally similar, independent of air mass. Overall, κ averaged 0.28, suggesting the presence of organic material in particles. This is consistent with previous model work and field measurements. There is a slight increase in κ with increasing particle size, indicating the addition of soluble, likely inorganic, material during cloud processing.