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Primary Biological Aerosol Particles (PBAPs) like fungal spores, bacteria, pollen, etc. are reported to constitute large fraction of the atmospheric aerosols. They are responsible for the spread of organisms and diseases throughout the biosphere and may impact atmospheric processes and the hydrological cycle by acting as ice nuclei (IN) and giant cloud condensation nuclei (CCN). Despite their importance in the biosphere and climate, continuous measurements of PBAPs in high time and size resolutions are not available for the Indian subcontinent. Here we report the first measurements of fluorescent biological aerosol particles (FBAPs) in India. The measurements were carried out using an ultraviolet aerodynamic particle sizer (UV-APS) in Munnar, a high altitude tropical site in southern India. The study was conducted for three consecutive months during the Southwest monsoon season (1.June.2014–21.August.2014), which is marked by heavy and persistent rainfall and strong Westerly/Southwesterly clean winds. Averaged over the entire campaign arithmetic mean number and mass concentrations of coarse-mode FBAP (> 1 μm) were 0.02 cm−3 and 0.24 µg−3, respectively, which corresponded to ~ 2 and 6 % of total aerosol loading, respectively. Average FBAP number size distribution exhibited a peak at ~ 3 μm, which was most likely contributed by fungal spores, as supported by scanning electron microscope (SEM) images, and the results are consistent with previous studies made for FBAP. During eleven weeks of measurements the corresponding total (TAP) coarse mode particle number concentration was highly variable in contrast to the variability observed in FBAP number concentration. Averaged over the entire campaign the TAP number and mass concentrations were 1.8 cm−3 and 7.0 µg m−3. The TAP and FBAP number concentrations measured at this site were strongly dependent on changes in wind direction and rainfall. During the period of continuous and persistent rainfalls the TAP and FBAP concentration exhibited very low concentration levels (1.3 cm−3 and 0.005 cm−3, respectively) with no observed diurnal variations. Averaged over the entire campaign FBAP exhibited a moderately diurnal variation with highest concentration during early morning hours (~ 06:00–08:00 hrs). The campaign averaged FBAP number concentrations were shown to correlate with daily patterns of meteorological parameters and were positively correlated with relative humidity (RH; R2 = 0.58), and negatively with temperature (R2 = 0.60) and wind speed (R2 = 0.60). We did not observe any significant positive correlation with precipitation as reported by previous researchers from selected areas. These measurement results confirms the fact that fraction of PBAPs to TAP is strongly dependent on size and location and thus may constitute significant proportion of total aerosol particles. [ABSTRACT FROM AUTHOR]

As part of the CLACE-6 campaign we performed size-resolved CCN measurements for a supersaturation range of S = 0.079% to 0.66% at the high-alpine research station Jungfraujoch, Switzerland, in March 2007. The derived effective hygroscopicity parameter κ describing the influence of particle composition on CCN activity was on average 0.23-0.30 for Aitken (50-100 nm) and 0.32-0.43 for accumulation mode particles (100-200 nm). The campaign average value of κ = 0.3 is similar to the average value of κ for other continental locations. When air masses came from southeasterly directions crossing the Po Valley in Italy, particles were much more hygroscopic (κ ≈ 0.42) due to large sulfate mass fractions. The κ values obtained at S = 0.079% exhibited a good negative correlation with the organic mass fractions derived from PM1 aerosol mass spectrometer (AMS) measurements. Applying a simple mixing rule the organic and inorganic mass fractions observed by the AMS could be used to reproduce the temporal fluctuations of the hygroscopicity of accumulation mode particles quite well. We show how during a cloud event the aerosol particles were activated as cloud droplets and then removed from the air by precipitation leaving behind only a small amount of accumulation mode particles consisting mainly of weakly CCN-active particles, most likely externally mixed unprocessed soot particles. During the campaign we had the opportunity to directly compare two DMT CCN counters for a certain time. The total CCN concentration (NCCN,tot) obtained by the two instruments at equal supersaturations agreed well for both possible operating modes: detecting NCCN,tot directly by sampling the polydisperse aerosol with the CCNC, or indirectly by combining size-resolved measurements of the activated fraction with parallel measurements of the particle size distribution (e.g., by SMPS). However, some supersaturation setpoints differed between the two CCNCs by as much as 20% after applying the instrument calibrations, which resulted in differences of the corresponding NCCN,tot of up to 50 %. This emphasizes that it is extremely important to carefully calibrate the supersaturation of the instrument, especially at low S. [ABSTRACT FROM AUTHOR]

As a part of the AMAZE-08 campaign during the wet season in the rainforest of Central Amazonia, an ultraviolet aerodynamic particle sizer (UV-APS) was operated for continuous measurements of fluorescent biological aerosol particles (FBAP). In the coarse particle size range (>1 µm) the campaign median and quartiles of FBAP number and mass concentration were 7.3x104 m-3 (4.0-13.2x104 m-3) and 0.72 µgm-3 (0.42-1.19 µgm-3), respectively, accounting for 24% (11-41 %) of total particle number and 47% (25-65 %) of total particle mass. During the five-week campaign in February- March 2008 the concentration of coarse-mode Saharan dust particles was highly variable. In contrast, FBAP concentrations remained fairly constant over the course of weeks and had a consistent daily pattern, peaking several hours before sunrise, suggesting observed FBAP was dominated by nocturnal spore emission. This conclusion was supported by the consistent FBAP number size distribution peaking at 2.3 µm, also attributed to fungal spores and mixed biological particles by scanning electron microscopy (SEM), light microscopy and biochemical staining. A second primary biological aerosol particle (PBAP) mode between 0.5 and 1.0 µm was also observed by SEM, but exhibited little fluorescence and no fungal staining. This mode consisted of single bacterial cells, brochosomes and various fragments of biological material. Particles liquid-coated with mixed organic-inorganic material constituted a large fraction of observations, and these coatings contained salts likely from primary biological origin. We provide key support for the suggestion that real-time laser-induce fluorescence (LIF) techniques provide size-resolved concentrations of FBAP as a lower limit for the atmospheric abundance of biological particles. We also show that primary biological particles, fungal spores in particular, are key fractions of supermicron aerosol in the Amazon and that, especially when coated by mixed inorganic material, could contribute significantly to hydrological cycling in such regions of the globe. [ABSTRACT FROM AUTHOR]

Soot particles are regarded as the most efficient light absorbing aerosol species in the atmosphere, playing an important role as a driver of global warming. Their climate effects strongly depend on their mixing state, which significantly changes their light absorbing capability and cloud condensation nuclei (CCN) activity. Therefore, knowledge about the mixing state of soot and its aging mechanism becomes an important topic in the atmospheric sciences. The size-resolved (30-320 nm diameter) mixing state of soot particles in polluted megacity air was measured at a suburban site (Yufa) during the CAREBeijing 2006 campaign in Beijing, using a Volatility Tandem Differential Mobility Analyzer (VTDMA). Particles in this size range with non-volatile residuals at 300 °C were considered to be soot particles. On average, the number fraction of internally mixed soot in total soot particles (Fin), decreased from 0.80 to 0.57 when initial Dp increased from 30 nm to 320 nm. Further analysis reveals that: (1) Fin was well correlated with the aerosol hygroscopic mixing state measured by a CCN counter. More externally mixed soot particles were observed when particles showed more heterogeneous features with regard to hygroscopicity. (2) Fin had pronounced diurnal cycles. For particles in the accumulation mode (Dp at 100-320 nm), largest Fin were observed at noon time, with "apparent" turnover rates (kex→in) up to 7.8%h-1. (3) Fin was subject to competing effects of both aging and emissions. While aging increases Fin by converting externally mixed soot particles into internally mixed ones, emissions tend to reduce Fin by emitting more fresh and externally mixed soot particles. Similar competing effects were also found with air mass age indicators. (4) Under the estimated emission intensities, actual turnover rates of soot (kex→in) up to 20%h-1 were derived, which showed a pronounced diurnal cycle peaking around noon time. This result confirms that (soot) particles are undergoing fast aging/coating with the existing high levels of condensable vapors in the megacity Beijing. (5) Diurnal cycles of Fin were different between Aitken and accumulation mode particles, which could be explained by the faster size shift of smaller particles in the Aitken mode. [ABSTRACT FROM AUTHOR]

This paper presents a new concept of hygroscopicity distribution for the analysis and modeling of aerosol particle hygroscopicity and Cloud Condensation Nucleus (CCN) activity. The cumulative particle hygroscopicity distribution function N(κ) is defined as the number concentration of particles with an effective hygroscopicity parameter, κ, smaller than the distribution argument κ. From Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA) measurement data, N(κ) can be directly derived by solving the κ-Köhler model equation. Similarly, measured CCN efficiency spectra (activation curves) can also be converted into N(κ), because the CCN measured at a fixed particle diameter and supersaturation (S) can be regarded as those particles with κ larger than a certain threshold value. Unlike studies calculating only one hygroscopicity parameter value from a CCN efficiency spectrum, the concept of N(κ) makes use of the information contained in each point of the spectrum. Model aerosols are used to explain the concept, and exemplary applications are shown with HTDMA and CCN field measurement data. [ABSTRACT FROM AUTHOR]

We report first measurements of ultrafine particles from a semi-rural location, Gadanki, from tropical Southern India. Measurements of particle number size distributions in the diameter range of 5 nm-32 µm were performed during 2 May-31 July 2012. The mean number concentrations of nucleation (NNUC), Aitken (NAIT), accumulation (NACCU), and total particles (NTOT) at this site were (1.1 ± 0.9) x 10³ cm-3, (2.2 ± 1.3) x 10³ cm-3, (1.5 ± 1.2) x 10³ cm-3 and (4.8 ± 2.4) x 10³ cm-3, respectively, comparable to other rural to semi-rural locations globally and declined as the season progressed, perhaps due to wet removal of aerosols with onset of monsoon in early June. Particle bursts in the nucleation mode size range (5-25 nm), followed by a sustained growth in size were observed very rarely (only 5 out of 79 observation days) at this site, less frequently than at most other locations around the world during May-July. Most factors affecting new particle formation (NPF) were similar on NPF and nonNPF event days, such as condensation sink, relative humidity, temperature, wind speed and direction, and mixing layer height. Thus, the infrequent occurrence of NPF at our site appeared to be linked to lower precursor gas concentrations and weak gas-phase oxidation chemistry due to diminished solar radiation on persistently cloudy days with the onset of the monsoon in early June over this region. The derived particle growth rates (GR > 5 nm) and formation rates of 5 nm particles (J5) ranged from 2.2 to 4.7 nm h-1 and 0.4-2.4 cm-3 s-1, with a mean and standard deviation of 3.4 ± 0.9 nm h-1 and 1.2 ± 2.3 cm-3 s-1, respectively, comparable to previous investigations at rural to semi-rural locations. The observed behavior in aerosol and meteorological parameters on NPF and nonNPF event days appeared to be distinctive compared to other rural to urban locations across the globe. However, this distinct behavior is limited and restricted to this site and season of the year, and should therefore not be generalized over a larger spatio-temporal scale. This emphasizes the need for long-term aerosol and precursor measurements over this and other regions of India. [ABSTRACT FROM AUTHOR]