Increase In Number Concentration Research Articles

Maritime Aerosol and CCN Profiles Derived From Ship‐Based Measurements Over Eastern North Pacific During MAGIC

AbstractAtmospheric aerosols are widely recognized to give rise to a substantial radiative forcing to the climate by scattering and absorbing radiation and by modifying the microphysical, lifetime, and radiative properties of clouds. During the Marine ARM GPCI Investigation of Clouds (MAGIC) over the Eastern North Pacific (ENP), the ship‐based measured cloud condensation nuclei (CCN) concentration at 0.2% supersaturation (NCCN,0.2) and condensation nuclei concentration (NCN) had mean values of 116.7 and 219.4 cm−3, with the highest concentrations found closest to LA due to an increase in aerosol sources. Moving westward, both NCCN,0.2 and NCN gradually decreased until stabilizing near 100 cm−3 and 200 cm−3, respectively. Using the methods proposed by Ghan and Collins (2004), https://doi.org/10.1175/1520-0426(2004)021<0387:uoisdt>2.0.co;2 and Ghan et al. (2006), https://doi.org/10.1029/2004jd005752, NCCN,0.2 profiles are retrieved using the surface measured NCCN,0.2 as a constraint. For coupled conditions, correlations between the retrieved NCCN,0.2 profiles and cloud‐droplet number concentration (NC) increase from 0.26 at the surface to 0.38 near cloud base, particularly true for non‐drizzling clouds. Although the correlations are lower than expected, the percentage increase (46.2%) is encouraging. Finally, the relationships between cloud breakup (CB) and the stratocumulus to cumulus transition (SCT) with environmental conditions and associated aerosols are also studied. The decreased NCN trend east of CB is mainly caused by precipitation scavenging, while the increased NCN trend west of CB is strongly associated with the increased surface wind speed and fewer drizzle events. A further study is needed using high‐resolution models to simulate these events.

The striking effect of vertical mixing in the planetary boundary layer on new particle formation in the Yangtze River Delta

New particle formation (NPF) induces a sharp increase in ultrafine particle number concentrations and potentially acts as an important source of cloud condensation nuclei (CCN). As the densely populated area of China, the Yangtze River Delta (YRD) region shows a high frequency of observed NPF events at the ground level, especially in spring. Although recent observational studies suggested a possible connection between NPF at the higher altitudes and ground level, the role played by vertical mixing, particularly in the planetary boundary layer (PBL) is not fully understood. Here we integrate measurements in Nanjing on 15–20 April 2018, and the NPF-explicit Weather Research and Forecast coupled with chemistry (WRF-Chem) model simulations to better understand the governing mechanisms of the NPF and CCN. Our results indicate that newly formed particles at the boundary layer top could be transported downward by vertical mixing as the PBL develops. A numerical sensitivity simulation created by eliminating aerosol vertical mixing suppresses both the downward transport of particles formed at a higher altitude and the dilution of particles at the ground level. The resulting higher Fuchs surface area at the ground level, together with the lack of downward transport, yields a sharp weakening of NPF strength and delayed start of NPF therein. The aerosol vertical mixing, therefore, leads to a more than double increase of surface CN10–40 and a one third decrease of boundary layer top CN10–40. Additionally, the continuous growth of nucleated ultrafine particles at the boundary layer top is strongly steered by the upward transport of condensable gases, with close to half increase of particle number concentrations in Aitken mode and CCN at a supersaturation rate of 0.75%. The findings may bridge the gap in understanding the complex interaction between PBL dynamics and NPF events, reducing the uncertainty in assessing the climate impact of aerosols.

Number concentration dependence of ultrasonic disruption ratio of diameter-sorted microcapsules.

The use of ultrasound to destroy microcapsules in microbubble-assisted drug delivery systems (DDS) is of great interest. In the present study, the disruption ratios of capsule clusters were measured by observing and experimentally analyzing microcapsules with polymer shells undergoing disruption by ultrasound. The microcapsules were dispersed in a planar microchamber filled with a gelatin gel and sonicated using 1 MHz focused ultrasound. Different capsule populations were obtained using a filtration technique to modify and control the capsule sizes. The disruption ratio as a function of the concentration of capsules was obtained through image processing of the recorded photomicrographs. We found that the disruption ratio for each population exponentially decreases as the particle number concentration (PNC) increases. The maximum disruption ratio of the diameter-sorted capsules was larger than that of polydispersed capsules. Particularly, for resonant capsule populations, the ratio was more than twice that of polydispersed capsules. Furthermore, the maximum disruption ratio occurred at higher concentrations as the mean particle diameter of the capsule cluster decreased.

Storm-Scale Polarimetric Radar Signatures Associated with Tornado Dissipation in Supercells

Abstract Polarimetric radar data from the WSR-88D network are used to examine the evolution of various polarimetric precursor signatures to tornado dissipation within a sample of 36 supercell storms. These signatures include an increase in bulk hook echo median raindrop size, a decrease in midlevel differential radar reflectivity factor (ZDR) column area, a decrease in the magnitude of the ZDR arc, an increase in the area of low-level large hail, and a decrease in the orientation angle of the vector separating low-level ZDR and specific differential phase (KDP) maxima. Only supercells that produced “long-duration” tornadoes (with at least four consecutive volumes of WSR-88D data) are investigated, so that signatures can be sufficiently tracked in time, and novel algorithms are used to isolate each storm-scale process. During the time leading up to tornado dissipation, we find that hook echo median drop size (D0) and median ZDR remain relatively constant, but hook echo median KDP and estimated number concentration (NT) increase. The ZDR arc maximum magnitude and ZDR–KDP separation orientation angles are observed to decrease in most dissipation cases. Neither the area of large hail nor the ZDR column area exhibit strong signals leading up to tornado dissipation. Finally, combinations of storm-scale behaviors and TVS behaviors occur most frequently just prior to tornado dissipation, but also are common 15–20 min prior to dissipation. The results from this study provide evidence that nowcasting tornado dissipation using dual-polarization radar may be possible when combined with TVS monitoring, subject to important caveats.

Pathways of precipitation formation in different thermodynamic and aerosol environments over the Indian Peninsula

This study examines precipitation pathways in different thermodynamic and aerosol environments over the Indian peninsula. A three-dimensional idealized Large-Eddy Simulation (LES) model with spectral bin microphysics is used to simulate convective clouds growing under different monsoon environments. Numerical simulations were evaluated using in-situ measurements from the Cloud-Aerosol Interactions and Precipitation Enhancement Experiment (CAIPEEX). Sensitivity studies were carried out using varied combinations of water vapor mixing ratio (by ±10 and ± 20%) and cloud condensation nuclei number concentrations (100 and 3000 cm−3). The response of various microphysical process rates to the changes in moisture and aerosol is analyzed. The clouds developed in a moist environment have a greater cloud depth, more supercooled liquid, broader cloud drop spectra, earlier onset of mixed-phase regimes, and enhanced precipitation. The amount of moisture is an important factor in determining the aerosol effects on cloud phase and precipitation, with a more significant aerosol impact in the moist environment (+ 20%). An increase in aerosol number concentration results in an enhanced mixed-phase fraction, updraft velocity, and precipitation, mainly through enhancing deposition and aggregation rates. The overall change in moisture by ±20% in cloud properties and precipitation is much more significant than the ten-times change in aerosol concentrations. The secondary ice formation via the Hallet-Mossop (H-M) process plays a significant role in determining the total ice crystal concentration, and its importance increases with the increases of both moisture and aerosol number concentration. The impact of this process on precipitation is minimal. These results provide an important understanding of how co-varied moisture and aerosols over the Indian region would affect the monsoon clouds and precipitation.

Numerical Analysis of the Impact of Complex Urban Environment on a Snowfall Event in Beijing

AbstractThe impacts of anthropogenic heat emissions, urban land use, and aerosols on a snowfall event in Beijing were investigated by using the Weather Research and Forecasting model. The results show that urban land use and anthropogenic heat emissions can reduce the accumulation of snowfall by 17%–22% within the fifth ring road, which depends on the aerosol number concentration and size. The increase in aerosols (same land use and anthropogenic heat emissions) can increase the accumulated snowfall within fifth ring road, especially for accumulated and coarse mode. Urban land use, anthropogenic heat emissions, and aerosols have different effect on snowfall, which depend mainly on relatively humidity. Urban land use and anthropogenic heat emissions lead to the formation of an “urban heat and dry island,” which is not favorable to snowfall processes during the initial snowfall processes and leads to a decrease in ice crystals and snow by 47% averaged. At this time, the increase in aerosol number concentrations has less impact (increase by 5% averaged) on snowfall because of higher supersaturation required for activation. With the development of snowfall processes, the feedback of cloud microphysics decrease temperature and increase relative humidity, which is favorable to snowfall process and increase snowfall slightly by 5% averaged. Meanwhile, the critical radius of aerosols that can be activated decrease, smaller particle aerosols are activated to form supercooled cloud water and further to form ice crystals and snow, which leads to an increase in accumulated snowfall by 11% averaged.

Numerical investigation of forced convective heat transfer of nanofluids within an enclosure

Heat transfer applications normally observed day-to-day are mainly focused on forced convection such as the transfer of hot fluid being pumped through pipes, shell and tube heat exchanger and power plants. The heat transfer characteristics of nanofluids present within a cubical enclosure subjected to forced convection is analysed here. Assisting and opposing forced convection flows are being compared. The inlet through which a nanofluid enters the cubical enclosure at a uniform velocity is positioned at the lower portion of the left wall for the assisting case and situated at the upper portion of the left wall for the opposing case. An in-house solver based on finite difference method is developed using simplified marker and cell algorithm (SMAC) through which the simulation is performed. The nanofluid chosen here is a water-based one with various nanoparticles such as aluminium (Al), silver (Ag), aluminium oxide (Al2O3) and singled wall carbon nanotubes (SWCNT) which are investigated for a Reynolds number range of 103 to 105. Other parametric studies like the volume concentration is also being varied from 0% to 3%. The results of this paper tend to show that heat transfer characteristics increase with an increase in both Reynolds number and volume concentration. Forced convection occurring through assisting flow case is showing better heat transfer than in the opposing flow case.

Impact of sub-grid particle formation in sulfur-rich plumes on particle mass and number concentrations over China

Particle formation in point source plumes is a typical sub-grid process not explicitly resolved in chemical transport models, and is an important contributor to atmospheric aerosols. The sub-grid particle formation (SGPF) is closely associated with the concentration of hydroxyl radical and condensation sinks in the plume, thus it has diurnal, seasonal and spatial variations. The impacts of SGPF in point source plumes on both aerosol mass and number concentrations were first investigated in China by a newly developed global nested chemical transport model with a SGPF parameterization scheme. Although a mean oxidation fraction of 2.5% sulfur dioxide for parameterizing the SGPF is suggested, the oxidation fraction and the particles formed in point source plumes have clear spatiotemporal variations based on the results of the SGPF scheme. The SGPF can enhance the annual mean concentration of sulfate by more than 1 μg m−3 (10–25%) over high emission areas (HEAs) in central-eastern China (CEC). In terms of particle number concentration, the SGPF contributes much more to nucleation mode particles with increasing number concentration, by 25–50% in HEAs, 10–25% in CEC, and 1–5% in northwestern China (NWC) compared with lower values (within ±5%) for the accumulation mode. This study reveals the significant impacts of SGPF over China and its strong dependence on meteorological and environmental factors. Physically-based SGPF scheme should be incorporated when studying the regional effects of point source plumes on air quality and climate.

The Effect of Ultrafine Particles (PM0.1) on Neurological Disorders in New York State

BACKGROUND AND AIM: Ultrafine particles (UFPs) are a significant air pollutant, yet related health research is rare. Among these studies, respiratory and cardiovascular outcomes have been analyzed far more than other health outcomes. This study evaluated the effects of UFP exposure on overall and various neurological disorders; and we examined if these associations differed by or interacted with social-demographics and meteorological factors. METHODS: We gathered emergency department (ED) visit data from New York State (NYS) Department of Health with a primary diagnosis of several neurological disorders in NYS from 2013-2018. The concentrations of UFPs and other air pollutants (as confounders) were obtained from high resolution simulations using a validated chemical transport model with size-resolved particle microphysics. We used a case-crossover design and conditional logistic regression to estimate the excess risk of ED admission for all neurological disorders and the sub-types of dementia, Parkinson’s disease, multiple sclerosis (MS), Amyotrophic Lateral Sclerosis (ALS), and stroke. We also analyzed interactions between UFP and gender, race, ethnicity, age, relative humidity (RH), temperature, and season. RESULTS:An inter-quartile range (IQR) increase in UFP number concentration increased general neurological disorders on individual lags (Lag 0 & 1: 0.7%, 95% CI: 0.1-1.2%) and all cumulative lags (Excessive Risk ranged from 0.7-1.4, all p0.05). UFP exposure also increased ED visits for dementia (1.4%; 95% CI: 0.1-1.2%), Parkinson’s disease (1.7%; 95% CI: 0.2-3.2%), and ALS (5.5%, 95% CI: 0.5-10.7%). Gender and age interacted with these health effects, with females and adults being more susceptible. Finally, mild temperatures (90th percentile) made individuals more vulnerable to UFP’s effects. CONCLUSIONS:Exposure to UFPs significantly increased the risk of ED visits for general neurological disorders across all lag days, especially for dementia Parkinson’s disease, and ALS. The associations varied by demographics and weather factors. More epidemiological research is needed to examine the relationships between UFPs and neurological health outcomes. KEYWORDS: Air pollution, neurological disorders, ultrafine particles

Enhancement of nanoparticle formation and growth during the COVID-19 lockdown period in urban Beijing

Abstract. Influenced by the spread of the global 2019 novel coronavirus (COVID-19) pandemic, primary emissions of particles and precursors associated with anthropogenic activities decreased significantly in China during the Chinese New Year of 2020 and the lockdown period (24 January–16 February 2020). The 2-month measurements of the number size distribution of neutral particles and charged ions showed that during the lockdown (LCD) period, the number concentration of particles smaller than 100 nm decreased by approximately 40 % compared to the pre-LCD period in January. However, the accumulation mode particles increased by approximately 20 % as several polluted episodes contributed to secondary aerosol formation. In this study, new particle formation (NPF) events were found to be enhanced in the nucleation and growth processes during the LCD period, as indicated by the higher formation rate of 2 nm particles (J2) and the subsequent growth rate (GR). The relevant precursors, e.g., SO2 and NO2, showed a clear reduction, and O3 increased by 80 % during LCD period, as compared with pre-LCD. The volatile organic vapors showed different trends due to their sources. The proxy sulfuric acid during the LCD period increased by approximately 26 %, as compared with pre-LCD. The major oxidants (O3, OH, and NO3) of VOCs were also found to be elevated during LCD. That indicated higher J2 and GR (especially below 5 nm) during the LCD period were favored by the increased concentration level of condensing vapors and decreased condensation sink. Several heavy haze episodes have been reported by other studies during the LCD period; however, the increase in nanoparticle number concentration should also be considered. Some typical NPF events produced a high number concentration of nanoparticles that intensified in the following days to create severe aerosol pollution under unfavorable meteorological conditions. Our study confirms a significant enhancement of the nucleation and growth process of nanoparticles during the COVID-19 LCD in Beijing and highlights the necessity of controlling nanoparticles in current and future air quality management.

Reduction in autumn precipitation over Southwest China by anthropogenic aerosol emissions from eastern China

Impacts of anthropogenic aerosols in China on autumn precipitation over Southwest China were investigated using version 5.1 of the Community Atmosphere Model. Simulations with and without anthropogenic aerosol emissions were compared to examine the effects of anthropogenic aerosols on surface air temperature and precipitation in East Asia. Our results show that the aerosol increase induces strong cooling over East Asia by aerosols' direct effect on radiation and indirect effect on clouds. Substantial reductions in precipitation are found across eastern China, but the largest decrease is in Southwest China. Anthropogenic aerosols cause a considerable increase in the cloud condensation nuclei number concentration and a decline in the cloud droplet effective radius in East Asia. The reduced cloud droplet sizes suppress the formation of precipitation and increase cloud depth and liquid water path. Consequently, aerosols' direct radiative effect as well as indirect effect on cloud depth and albedo significantly reduce the shortwave radiation for all sky between 20°and 40°N in China. More absorbing aerosols in the lower troposphere increase shortwave radiative heating, which possibly burns off low-level convective clouds and could cause significant reductions in condensational heating in the lower troposphere. The patterns of the shortwave heating increase and condensational heating reduction are generally consistent with significant reductions in the convective precipitation over China. We further investigated other factors governing precipitation and found moderate stability enhancement and moisture transport reductions in most of China, both of which partially contribute to a decrease in the convective precipitation in Southwest China. Aerosols' direct and indirect effects reduce the amount of solar radiation reaching the surface and cool the surface and lower troposphere between 20° and 40°N, causing anomalous subsidence and reductions in the large-scale precipitation over central and eastern China. Both convective and large-scale precipitation are suppressed over Southwest China, leading to a significant decrease in total precipitation over this area.

Characteristics of CCN activation and cloud microphysics over the east coast of India during the Northeast Monsoon onset

Airborne observations conducted during the Northeast Monsoon onset as part of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX 2011) are used to link the activation properties of aerosols with the observed cloud microphysics. This study illustrates the significant spatial variability in the aerosol spectrum, cloud condensation nuclei (CCN) activation characteristics, and the cloud droplet spectral properties over a coastal and an inland location. High concentrations of Aitken mode and black carbon aerosols were observed in the free troposphere and are attributed to the convectively transported smoke and aerosols from the coastal boundary layer. The assumption of an internally mixed organic and inorganic aerosol composition provided a better CCN closure over assumptions of either purely organic or purely inorganic aerosols. The coastal clouds were equally polluted as the inland clouds with high cloud droplet number concentrations near the cloud base. The vertical distribution of cloud droplet spectral characteristics was similar in both coastal and inland clouds. An increase in droplet number concentration up to 2 km above the cloud base indicated a prominent influence of submicron particles on the cloud microphysical parameters. Evidence for an enhanced concentration of supercooled drops above the freezing level up to temperatures below −12 °C is documented. The secondary ice production was evident through observations of graupel and snow particles. Heavy loading of aerosols near the cloud base leads to enhanced mixed-phase processes in these clouds.

Effects of aerosols on cloud and precipitation in East‐Asian drylands

AbstractExtensive observational and numerical simulations have been performed to better characterize the role of aerosols in affecting the clouds and precipitation. However, due to the large uncertainties of aerosol property, the effect of aerosols on clouds and precipitation over the arid and semiarid region (briefly called ‘drylands’) of East Asia (EA) is still unclear. Basing on observations and model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5), we investigated the aerosol's effects on the cloud properties and precipitation over the drylands of EA from 1850 to the present and projected forward to 2,300. It is found that, during 1850–2005, with the mean aerosol optical depth (AOD) over the drylands of EA increasing, the cloud droplet number concentration (CDNC) increases, while the cloud effective droplet radius (CEDR) decreases significantly at a rate of −0.40 μm·century−1. Besides, the cloud water path (CWP) and precipitation show slightly increasing trends with the AOD increasing. Additionally, the effect of aerosols on cloud properties is saturated when the AODs reach 0.21 and 0.15 over the arid region (AR) and semiarid region (SR), respectively. According to the prediction for the period 2006–2300, the AOD and CDNC tend to decline over the drylands of EA, while the CWP, CEDR and precipitation show increasing trends. Particularly, the aerosol, clouds and precipitation indicate more significant changes over the SR in EA during 2006–2300. In future research, there is an urgent need to quantify the contribution of aerosol‐cloud interaction to the precipitation change over the drylands of EA.

Aerosol dynamics modeling of sub-500 nm particles during the HOMEChem study.

We spend most of our time in built environments. The cumulative exposure to particulate matter (PM) occurring in these built environments can potentially be comparable to or even exceed that occurring outdoors. Therefore, it is critical to understand the sources, dynamics, and fate of PM in built environments. This work focuses on aerosol dynamics modeling (including coagulation, deposition, and exfiltration) of sub-500 nm particles measured inside a test house during the HOMEChem campaign while performing prescribed cooking activities. Deposition characteristics of the test house, emission rates and factors, and the fate of particles are presented. Number emission rates calculated for two different heat sources (stove and hot plate) and the various meals cooked on them were highest for sub-10 nm particles. Coagulation and deposition contributed comparably to the particle number concentration decay. Most of the PM (90% number-based and 70% mass-based) deposited within the house while the remaining fraction left the test house volume via exfiltration. Simulation results show that while increased air exchange rate reduces indoor PM mass concentration, it can lead to increased number concentration. An increase from 0.5 to 5 ACH (comparable to the equivalent air change rate from running a well-dimensioned portable air cleaner) would result in a 70% reduction in PM mass-based exposure while a further increase from 5 to 20 ACH would only result in an additional 21% reduction.

Geoengineering: Impact of Marine Cloud Brightening Control on the Extreme Temperature Change over East Asia

We investigated the effect of artificial marine cloud brightening on extreme temperatures over East Asia. We used simulation data from five global climate models which have conducted the GeoMIP G4cdnc experiment. G4cdnc was designed to simulate an increase in the cloud droplet number concentration of the global marine lower clouds by 50% under the greenhouse gas forcing of the RCP4.5 scenario. G4cdnc decreased the net radiative forcing in the top of the atmosphere more over the ocean, alleviating the rise in mean temperature under RCP4.5 forcing. For extreme temperatures, G4cdnc reduced both the monthly minimum of daily minimum temperature (TNn) and monthly maximum of daily maximum temperature (TXx). The response of TNn was higher than that of TXx, especially in the winter, over the Sea of Okhotsk and the interior of the continent. This spatial heterogeneity and seasonality of the response were associated with sea ice–albedo and snow–albedo feedbacks. We also calculated the efficacy of warming mitigation as a measure of the relative effect of geoengineering. The efficacy for TXx was higher than that for TNn, opposite to the absolute effect. After the termination of geoengineering, both TNn and TXx tended to rapidly revert to their trend under the RCP4.5 forcing.

Nanoparticle Exposure and Workplace Measurements During Processes Related to 3D Printing of a Metal Object.

Metal 3D printing has many potential uses within prototyping and manufacturing. Selective laser melting (SLM) is a process that uses metal powders in the micrometer range as printing material. The particle release from the entire SLM printing process is not well-studied. While the 3D printing itself often occurs in a sealed chamber, activities related to the process can potentially release harmful metal particles to the indoor working environment through resuspension of the printing powder or via incident nanoparticles generated during printing. The objective of this study was to improve the understanding of particle exposure in work processes associated with 3D printing and potential needs for interventions by a case study conducted in a 3D printing facility. In this setting, direct release and dispersion of particles throughout the workspace from processes related to metal 3D printing was investigated. The release from five activities were studied in detail. The activities included post-printing cleaning, object annealing, and preparation of new base substrate for the next printing was. Three of the five measured activities caused particles number concentrations in the working environment to increase above background levels which were found to be 8·102 cm−3. Concentrations during chamber emptying and the open powder removal system (PRS) cleaning processes increased to 104 and 5·103 cm−3, respectively, whereas grinding activity increased number concentrations to 2.5·105 cm−3. Size distributions showed that particles were mainly smaller than 200 nm. Respirable mass concentrations were 50.4 μg m−3, collected on filters. This was corroborated by respirable mass measured with a DustTrak of 58.4 μg m−3. Respirable mass concentrations were below the occupational exposure limits in Denmark for an 8 h time-weighted average.

A Major Combustion Aerosol Event Had a Negligible Impact on the Atmospheric Ice‐Nucleating Particle Population

AbstractClouds containing supercooled water are important for both climate and weather, but our knowledge of which aerosol particle types nucleate ice in these clouds is far from complete. Combustion aerosols have strong anthropogenic sources, and if these aerosol types were to nucleate ice in clouds, they might exert a climate forcing. Here, we quantified the atmospheric ice‐nucleating particle (INP) concentrations during the United Kingdom's annual Bonfire Night celebrations, which are characterized by large amounts of combustion aerosol from bonfires and fireworks. We used three immersion mode techniques covering more than 6 orders of magnitude in INP concentration over the temperature range from −10°C to homogeneous freezing. We found no observable systematic change in the INP concentration on three separate nights, despite more than a factor of 10 increase in aerosol number concentrations, up to a factor of 10 increase in PM10 concentration, and more than a factor of 100 increase in black carbon (BC) mass concentration relative to pre‐event levels. This implies that BC and other combustion aerosol such as ash did not compete with the INPs present in the background air. Furthermore, the upper limit of the ice‐active site surface density, ns(T), of BC generated in these events was shown to be consistent with several other recent laboratory studies, showing a very low ice‐nucleating activity of BC. We conclude that combustion aerosol particles similar to those emitted on Bonfire Night are at most of secondary importance for the INP population relevant for mixed‐phase clouds in typical midlatitude terrestrial locations.

A Multiscale Analysis of a Nocturnal Extreme Rainfall Event of 14 July 2017 in Northeast China

AbstractA multiscale observational analysis of a nocturnal extreme rainfall event that occurred at Changtu in Northeast China on 14 July 2017 is performed using global analysis, automated surface observations, Doppler radar, rawinsonde, and disdrometer data. Results show that the large-scale environment was characterized by high convective available potential energy and precipitable water, moderate convective inhibition, and a southwesterly low-level jet (LLJ) capped by an inversion layer. The first and subsequent convective cells developed along a quasi-stationary surface convergence zone in a convection-void region of a previously dissipated meso-α-scale convective line. Continuous convective initiation through backbuilding at the western end and the subsequent merging of eastward-moving convective cells led to the formation of a near-zonally oriented meso-β-scale rainband, with reflectivity exceeding 45 dBZ (i.e., convective core intensity). This quasi-stationary rainband was maintained along the convergence zone by the LLJ of warm moist air, aided by local topographical lifting and convectively generated outflows. A maximum hourly rainfall amount of 96 mm occurred during 0200–0300 Beijing standard time as individual convective cores with a melting layer of >55 dBZ reflectivity moved across Changtu with little intermittency. The extreme-rain-producing stage was characterized with near-saturated vertical columns, and rapid number concentration increases of all raindrop sizes. It is concluded that the formation of the meso-β-scale rainband with continuous convective backbuilding, and the subsequent echo-training of convective cores with growing intensity and width as well as significant fallouts of frozen particles accounted for the generation of this extreme rainfall event. This extreme event was enhanced by local topography and the formation of a mesovortex of 20–30 km in diameter.

Impact of vacuum cleaning on indoor air quality

Vacuum cleaning can be a household source of particulate matter (PM) both from the vacuum motor and from settled dust resuspension. Despite the evidence of this contribution to PM levels indoors, the effect of this source on PM composition is still unknown. In this study, four vacuum cleaners (washable filter bag less, wet, bagged and HEPA filter equipped robot) were tested for the emission rate of particulate mass and number. The detailed PM chemical characterisation included organic and elemental carbon, metals and organic speciation. PM10 emission rates from bagged vacuum operation were much higher (207 ± 99.0 μg min−1) compared with the ones obtained from wet (86.1 ± 16.9 μg min−1) and washable filter bag less vacuums (75.4 ± 7.89 μg min−1). Particle (8–322 nm) number emission rates ranged from 5.29 × 1011 (washable filter bag less vacuum) to 21.2 × 1011 (wet vacuum) particles min−1. Ratios of peak to background levels indicate that vacuuming can elevate the ultrafine particle number concentrations by a factor ranging from 4 to 61. No increase in PM mass or number concentrations was observed during the HEPA filter equipped vacuum operation. The increase in copper and elemental carbon PM10 contents during vacuuming suggested motor emissions. Organic compounds in PM10 included alkanes, PAHs, saccharides, phenolics, alcohols, acids, among others. However, it was not possible to establish a relationship between these compounds and vacuuming due to the vast array of possible household sources. The cancer risks associated with metals and PAH inhalation were negligible.

Overview of aerosol optical properties over southern West Africa from DACCIWA aircraft measurements

Abstract. Southern West Africa (SWA) is an African pollution hotspot but a relatively poorly sampled region of the world. We present an overview of in situ aerosol optical measurements collected over SWA in June and July 2016 as part as of the DACCIWA (Dynamics-Aerosol-Chemistry-Clouds Interactions in West Africa) airborne campaign. The aircraft sampled a wide range of air masses, including anthropogenic pollution plumes emitted from the coastal cities, long-range transported biomass burning plumes from central and southern Africa and dust plumes from the Sahara and Sahel region, as well as mixtures of these plumes. The specific objective of this work is to characterize the regional variability of the vertical distribution of aerosol particles and their spectral optical properties (single scattering albedo: SSA, asymmetry parameter, extinction mass efficiency, scattering Ångström exponent and absorption Ångström exponent: AAE). The first findings indicate that aerosol optical properties in the planetary boundary layer were dominated by a widespread and persistent biomass burning loading from the Southern Hemisphere. Despite a strong increase in aerosol number concentration in air masses downwind of urban conglomerations, spectral SSA were comparable to the background and showed signatures of the absorption characteristics of biomass burning aerosols. In the free troposphere, moderately to strongly absorbing aerosol layers, dominated by either dust or biomass burning particles, occurred occasionally. In aerosol layers dominated by mineral dust particles, SSA varied from 0.81 to 0.92 at 550 nm depending on the variable proportion of anthropogenic pollution particles externally mixed with the dust. For the layers dominated by biomass burning particles, aerosol particles were significantly more light absorbing than those previously measured in other areas (e.g. Amazonia, North America), with SSA ranging from 0.71 to 0.77 at 550 nm. The variability of SSA was mainly controlled by variations in aerosol composition rather than in aerosol size distribution. Correspondingly, values of AAE ranged from 0.9 to 1.1, suggesting that lens-coated black carbon particles were the dominant absorber in the visible range for these biomass burning aerosols. Comparison with the literature shows a consistent picture of increasing absorption enhancement of biomass burning aerosol from emission to remote location and underscores that the evolution of SSA occurred a long time after emission. The results presented here build a fundamental basis of knowledge about the aerosol optical properties observed over SWA during the monsoon season and can be used in climate modelling studies and satellite retrievals. In particular and regarding the very high absorbing properties of biomass burning aerosols over SWA, our findings suggest that considering the effect of internal mixing on absorption properties of black carbon particles in climate models should help better assess the direct and semi-direct radiative effects of biomass burning particles.