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Many atmospheric aerosols are cloud condensation nuclei (CCN), capable of activating as cloud droplets when the relative humidity exceeds 100 %. Some primary biological aerosol particles (PBAPs), such as plant spores, pollen, or bacteria, have been identified as such CCN. Urban environments are a source of these bioaerosols, some of which are naturally produced by the local flora or are transported from surrounding regions and others of which are a result of human activities. In the latter case, open sewage, uncovered garbage, mold or other products of such activities can be a source of PBAPs. There have been relatively few studies, especially in the tropics, where PBAPs and CCN have been simultaneously studied to establish a causal link between the two. The metropolis of San Juan, Puerto Rico, is one such urban area with a population of 2 448 000 people (as of 2020). To better understand the fluorescent characteristics and cloud-forming efficiency of aerosols in this region, measurements with a wideband integrated bioaerosol spectrometer (WIBS), a condensation nuclei (CN) counter and a CCN spectrometer were made at the University of Puerto Rico – Río Piedras Campus. Results show that the CCN / CN activation ratio and the fraction of fluorescing aerosol particles (FAPs) have repetitive daily trends when the FAP fraction is positively correlated with relative humidity and negatively correlated with wind speed, consistent with previous studies of fungi spores collected on substrates. The results from this pilot study highlight the capabilities of ultraviolet-induced fluorescence (UV-IF) measurements for characterizing the properties of FAPs as they relate to the daily evolution of PBAPs. The use of multiple excitation and emission wavelengths, along with shape detection, allows the differentiation of different PBAP types. These measurements, evaluated with respect to previous, substrate-based analysis of the local fungal and pollen spores, have established a preliminary database of measurements that future, longer-term studies will build upon.

The present study, first over tropics, presents a quantitative approach to characterize aerosol mixing state over an urban location. A differential mobility analyzer (DMA)-single particle soot photometer (SP2) setup was designed to quantify size selected refractory black carbon (rBC) mixing state. Aerosols of size 70, 100, 200, 300, 400 and 500 nm were selected using DMA after which rBC mass concentration, and mixing state quantification were deduced using SP2. Strong correlation exists between rBC mass concentrations and particle number concentrations suggesting that most possible source of rBC is roadways traffic. Observations revealed that refractory externally mixed and internally core-shell mixed BC aerosol population decrease with increase in particle size, while the trend reversed for nonrefractory aerosols. Mixing state information shows that particles at lower size (70 nm) are mostly externally mixed rBC (78.7%), whereas particles at higher size (500 nm) are nonrefractory (74.2%). Further aerosols at lower sizes are more (7.5%) internally core-shell mixed BC particles, whereas higher size particles are less (2.9%) internally core-shell mixed. Particle population near 100 nm has relatively equal number of refractory and nonrefractory particles, however, populations differ below and above 100 nm. These results are important and highlight that aerosols near 100 nm are neutral, and act as barrier for equilibrium mixing of aerosol population. This study offers new insights to connect aerosol physical and chemical processes to evolution of aerosol mixing state as aerosol populations near, below and above 100 nm have different implications to optical and hygroscopic properties of aerosols, and climate.

Many types of atmospheric aerosols cloud condensation nuclei (CCN) capable of activating as cloud droplets. Some primary biological aerosol particles (PBAP), such as plant spores, pollen, or bacteria, have been identified as such CCN. Urban environments are a source of these bioaerosols, those that are naturally produced by the local flora, or are transported from surrounding regions, and others that are a result of human activities. In the latter case, open sewage, uncovered garbage, mold or other products of such activities can be a source of PBAPs. There have been relatively few studies, especially in the tropics, where PBAPs and CCN have been simultaneously studied to establish a causal link between the two. The metropolis of San Juan, Puerto Rico is one such urban area with a population of 2,448,000 (as of 2020). To better understand the fluorescent characteristics and cloud forming efficiency of aerosols in this region, measurements with a Wideband Integrated Bioaerosol Spectrometer (WIBS), a condensing nuclei (CN) counter, and a CCN spectrometer were made at the University of Puerto Rico – Rio Piedras Campus. Results show that the CCN / CN activation ratio and the fraction of fluorescing aerosol particles (FAP) have repetitive daily trends when the FAP fraction is positively correlated with relative humidity and negatively correlated with wind speed, consistent with previous studies of fungi spores collected on substrates. The results from this pilot study highlight the capabilities of ultraviolet-induced fluorescence (UV-IF) measurements for characterizing the properties of FAP as they relate to daily evolution of PBAPs. The use of multiple excitation and emission wavelengths, along with shape detection, allows the differentiation of different PBAP types. These measurements, evaluated with respect to previous, substrate-based analysis of the local fungal and pollen spores, have established a starting database of measurements that future, longer term studies will build upon.

The objective of this study is to characterise urban refractory black carbon (rBC) mixing state relative to hygroscopic growth factor (HGF) of size selective aerosols to better constrain the aerosol indirect effect. The Aitken mode range (≤100 nm) is dominated by particles that have relatively low hygroscopicity and comprised freshly emitted hydrophobic rBC, however, our observations suggest that BC mixing states in Aitken range (down to 70 nm) still govern the hygroscopic properties. Conversely, the accumulation mode range (>100 nm) dominated by particles that have relatively high hygroscopicity consisted of oxidized organic compounds and inorganic salts. Single particle soot photometer (SP2) measurement further revealed that particles at lower size are mostly incandescent type dominated by refractory component whereas higher size particles are mostly scattering type dominated by nonrefractory component. The lower hygroscopicity parameter (κ) (0.26 ± 0.08) obtained for Aitken mode particles suggests that they may contain levoglucosan and levoglucosan-OH oxidation products, and are possibly from biomass burning sources whereas accumulation range particles with higher κ value (0.39 ± 0.03) have ammonium sulfate, ammonium bisulfate and malonic acid in their composition and their possible source would be secondary in origin. These findings are important because for the first time, BC mixing state and the impact of size selective rBC on HGF are determined directly over an urban region which have implications to precipitation.

Aerosol size distributions were measured using a scanning mobility particle sizer (SMPS), and also PM1 (particulate matter ≤ 1 μm in aerodynamic diameter) samples were collected in parallel at a representative site in New Delhi during spring in 2013 and 2014. Based on the temporal variation of particle count mean diameter (CMD), sampling periods are characterized as growth events and non-growth events. Particle size distribution measurements suggest that some consecutive nights experienced unique nighttime subsequent growth of particles, which sustained for a longer period. Average particle growth rate measured during growth events was 5.64 ± 3.03 nm h−1. Atmospheric trace gas concentrations and meteorological data show that these growth events (nighttime) are influenced by higher concentrations of gases, e.g., NO2 (56.5 ± 29.7 μg m−3), SO2 (9.34 ± 1.14 μg m−3) and RH (45.7 ± 9.5%) than those of non-growth events (daytime) (37.9 ± 18.6 μg m−3, 7.19 ± 2.08 μg m−3 and 37.7 ± 6.9%, respectively). Further, analysis of PM1 samples collected during the study period shows that the particulate water-soluble organic carbon (WSOC) (12.7 ± 4.1 μg m−3), NH4+ (9.4 ± 3.2 μg m−3), SO42− (2.03 ± 0.70 μg m−3), K+(1.06 ± 0.40 μg m−3), and NO2− + NO3− (0.59 ± 0.36 μg m−3) are the major contributors of particulate mass, wherein NH4+, SO42−, K+, NO2− + NO3− mass concentrations were higher during growth events. Correlation study shows that nighttime aerosol composition during growth (in sub-micron range) events are more enriched by inorganic species (i.e., NH4NO3, (NH4)2SO4 and H2SO4 vapors) as compared to organics (i.e., WSOC, does not show much difference in growth events and non events). Our results suggest that nighttime sulfate formation at the site is mostly mediated by high NO2 and NH3 at elevated RH. For the formation of sulfate and other inorganic species, a nighttime atmospheric chemistry is proposed, which is linked to particle growth. Growth events observed typically in nighttime have both biomass burning and anthropogenic influences as indicated by high concentrations of WSOC, K+ and black carbon in PM1 and carbon monoxide in gas phase.

Traditionally, the atmospheric particle composition is analyzed using destructive methods. In general, the destructive methods lead to the destruction of the samples, higher cost of the analysis and larger analysis time. In view of aforesaid, in current work, we present a method for the non-destructive analysis of atmospheric particles using open path-Fourier transform infrared spectroscopy (OP-FTIR). The developed method has been used for the measurement of ammonium and sulfate in atmospheric particles without destroying the samples. Here, we targeted the said species because of their relative importance for air pollution episode formation. Particulate sulfate plays a major role in formation of haze. However; particulate acidity is an important factor in this process, which is governed by particulate ammonium concentration. Therefore, both SO42− and NH4+ are important as far as atmospheric chemistry of haze formation is concerned. In the present study, the qualitative and quantitative estimation of ammonium and sulfate ions in PM2.5 (particulate matter with aerodynamic diameter less than 2.5 µm) was carried out using OP-FTIR with the developed method. The seasonal average concentration of NH4+ and SO42− were measured to be 12.00 ± 5.80, 31.71 ± 12.71 µg/m3 respectively for winters, 3.00 ± 0.85 and 8.00 ± 2.28 µg/m3 respectively for summers and 2.60 ± 1.90 and 7.00 ± 5.21 µg/m3 respectively for monsoon season. The observed results are found to be in good agreement with that of other studies using destructive methods.

Open-waste burning (OWB) is one of the primary sources of urban aerosols in several developing countries. To better understand the influence of OWB emissions on urban aerosols, total suspended particles (TSP) and size-segregated samples were collected at an open-waste burning site (the Okhla landfill) and two urban sites in New Delhi. The TSP samples were analysed for selected metals (As, Cd, Cr, Cu, Fe, Ni, Pb, Sb, Se, Sn, Sr, V and Zn) using ICP-MS. In general, among the metals, Fe and Zn were mostly dominant, and As, Cd and Se were found in trace concentrations in the majority of the samples. Additionally, Pb concentrations were ~5–8 fold higher in urban wintertime samples than other samples. Tin, a tracer for waste-burning aerosols, ranged between 0.055 and 0.675 µg m–3 in OWB aerosols. Interestingly, the concentration of Sn was significantly high in the urban wintertime aerosols, specifically, 0.082–0.284 µg m–3. Tin also showed a high enrichment factor in the urban wintertime aerosols, suggesting its anthropogenic origin, possibly because of enhanced OWB practices in winter. Waste burning was also found to be one of the primary sources of chromium, which ranged between 0.102 and 0.606 µg m–3 in OWB aerosols and between 0.114 and 0.574 µg m–3 in urban aerosols. Since Cr(VI) is of interest due to its impact on health, the soluble Cr(VI) concentration was determined and found to be 6.12–10.2 ng m–3 (~1–6% of the total Cr in OWB aerosols compared to 0.33–0.65 ng m–3 [< 1% of the total Cr]) in urban aerosols. The lead isotopic signatures of OWB aerosols, viz., the 208Pb/206Pb and 206Pb/207Pb ratios, were determined to be 2.1309 ± 0.0029 and 1.1316 ± 0.0035, whereas those of the urban aerosols were 2.1369 ± 0.0026 and 1.1243 ± 0.0024, respectively. However, the ranges of these values among the different aerosol types were not very distinct and showed discreet overlaps. This Pb isotopic study, along with metal fingerprints, suggests the increased influence of OWB emissions in winter on New Delhi aerosols.

During March 20–22, 2012 Delhi experienced a massive dust-storm which originated in Middle-East. Size segregated sampling of these dust aerosols was performed using a nine staged Andersen sampler (5 sets of samples were collected including before dust-storm (BDS)), dust-storm day 1 to 3 (DS1 to DS3) and after dust storm (ADS). Sugars (mono and disaccharides, sugar-alcohols and anhydro-sugars) were determined using GC–MS technique. It was observed that on the onset of dust-storm, total suspended particulate matter (TSPM, sum of all stages) concentration in DS1 sample increased by > 2.5 folds compared to that of BDS samples. Interestingly, fine particulate matter (sum of stages with cutoff size 2.5 folds as compared to that of BDS samples. Sugars analyzed in DS1 coarse mode (sum of stages with cutoff size > 2.1 μm) samples showed a considerable increase (~ 1.7–2.8 folds) compared to that of other samples. It was further observed that mono-saccharides, disaccharides and sugar-alcohols concentrations were enhanced in giant (> 9.0 μm) particles in DS1 samples as compared to other samples. On the other hand, anhydro-sugars comprised ~ 13–27% of sugars in coarse mode particles and were mostly found in fine mode constituting ~ 66–85% of sugars in all the sample types. Trehalose showed an enhanced (~ 2–4 folds) concentration in DS1 aerosol samples in both coarse (62.80 ng/m3) and fine (8.57 ng/m3) mode. This increase in Trehalose content in both coarse and fine mode suggests their origin to the transported desert dust and supports their candidature as an organic tracer for desert dust entrainments. Further, levoglucosan to mannosan (L/M) ratios which have been used to predict the type of biomass burning influences on aerosols are found to be size dependent in these samples. These ratios are higher for fine mode particles, hence should be used with caution while interpreting the sources using this tool.

In aerosol research, differential mobility analyzer (DMA) is widely used for particle size distribution measurements. In general polystyrene latex (PSL) particle size standards are used to calibrate the DMAs. However, these standards are expensive, and their shelf-life is limited. Therefore in this work, we have used PSL particle standard of sizes 60 and 100 nm (SRM® 1964 and SRM® 1963a, respectively) and checked their performance within and after the shelf-life period for 3 consecutive years (2013 – 2015) using a calibrated DMA (i.e., long-DMA, TSI 3081). Also the size results are compared using a reference DMA (i.e., nano-DMA, TSI 3085). Using both long- and nano-DMA, the detail results of standard particle size measurements and involved uncertainties are discussed in this paper. We observed a continuous increase in the count mean diameter (CMD) calculated from the size distribution of each standard particle size with the progress of time. Particle size measured for PSL 60 and 100 nm using long-DMA are (56.01±5.56) nm and (92.86±10.81) nm in 2013, (56.37±5.66) nm and (93.71±10.44) nm in 2014, and (57.42±5.84) nm and (94.79±9.68) nm in 2015, respectively. Whereas, these results when nano-DMA was used are (56.82±4.32) nm and (94.62±9.46) nm in 2014, and (58.08±4.98) nm and (95.15±9.12) nm in 2015, respectively. Uncertainty results show that the components which contribute significantly in total uncertainty (at k =2) in CMD measurements are DMA sheath flow rate, DMA calibration, difference in certified and measured diameter, and variation in the ambient temperature and pressure. The size measurement results obtained from long-DMA and nano-DMA agreed well. Based on the measurement results, we suggest that the increasing trend of particle sizes (CMDs) with the progress of time from 2013 to 2015 is possibly because of the coating of contaminant residues (present in the standard liquid suspension) on the surface of the PSL particles which is further observed by high resolution tunnelling electron microscope (HRTEM) images of particles. Particles standards are stable and well characterized more than two years even after their shelf-life within the uncertainty limits. Size performance results for PSL 60 nm using calibrated long- and reference nano-DMA show good agreement with the size value given in the certificate, however standard PSL 100 nm size is found to be underestimated by ~7%.

The scanning mobility particle sizer (SMPS) technique is a widely employed technique to measure the particle number size distribution, and thus calculate the particle total growth rate. However, growth due to individual atmospheric processes needs to be known precisely and accurately to better model the secondary aerosol distribution. In this study, we use simplified analytical formulas to calculate the growth rates due to self-coagulation, coagulation scavenging and condensation processes of particle size distribution (9-425 nm) measured using SMPS. Firstly, total growth rate is determined from the regression fit of SMPS data plotted between the geometric mean diameter (GMD) of particle size (nm) versus time (hour) measured during a particle growth event. The SMPS measurements were conducted during November-December 2011 in New Delhi. The particle growth event days and non-event days were classified according to the protocol discussed elsewhere. Assuming that the particle number size distribution of a growing population can be described by a unimodal distribution and particles are neutral in the population, we calculated the growth rate due to selfcoagulation (GR_(scoag)), which is proportional to the total number of particles in the mode and mode peak diameter. Similarly, assuming that particles with mode peak size 25 nm and above act as a coagulation sink and grow due to scavenging of newly formed nucleation range particles (＜ 12 nm), we calculated the coagulation scavenging growth rate (GR_(scav)) as a time derivative of the mode peak diameter, which is equivalent to the product of particle diameter and its coagulation sink. The condensation growth rate (GR_(cond)) is calculated based on the assumption that total growth rate is the summation of the growth resulting of three physical processes: self-coagulation, coagulation scavenging and condensation. During the study period, three event days were recorded at the measurement site. To explain the growth rate calculation approach, which is presented here in detail, we have taken SMPS data of one event day (November 4, 2011) as an example (two other event days are also briefly discussed). On November 4, the total average growth rate was found to be 15.4 ± 11 nm/h, while the average GR_(scoag), GR_(scav) and GR_(cond) were calculated to be 3.8 ± 0.4 (with min and max values of 2.9-5.1 nm/h), 8.0 ± 6 (0.6-19.3 nm/h) and 3.6 nm/h, respectively. These growth rates are comparable to those reported for other urban sites around the world using different methods. This approach is simple, and growth by individual processes can be calculated without knowing several other parameters, which include vapor concentration of atmospheric constituents, heterogeneous processes, and complex modeling procedures.

The coal is contaminated with toxic metals at the trace levels. They are released into the environment during mining, handling and burning of coal. The Korba basin has one of the largest coal exploitation areas in the country. In this work, contamination and sources of toxic metals i.e. Hg and Pb in the air, soil and sediment of the Korba basin, India are described. The concentration of Hg and Pb in the ambient air was ranged from 7.4 - 29 and 7.0 - 585 ng/m3 with mean value of 18 ± 4 and 129 ± 104 ng/m3 in the winter season. The mean concentration of Hg in the soil and sediment was 0.22 ± 0.03 and 0.44 ± 0.08 mg/kg, respectively. The higher concentration of Pb in the environmental samples was observed.

In this work, we have used a scanning mobility particle sizer (SMPS) and a quartz crystal microbalance (QCM) to estimate the effective density of aerosol particles. This approach is tested for aerosolized particles generated from the solution of standard materials of known density, i.e. ammonium sulfate (AS), ammonium nitrate (AN) and sodium chloride (SC), and also applied for ambient measurement in New Delhi. We also discuss uncertainty involved in the measurement. In this method, dried particles are introduced in to a differential mobility analyser (DMA), where size segregation is done based on particle electrical mobility. Downstream of the DMA, the aerosol stream is subdivided into two parts. One is sent to a condensation particle counter (CPC) to measure particle number concentration, whereas the other one is sent to the QCM to measure the particle mass concentration simultaneously. Based on particle volume derived from size distribution data of the SMPS and mass concentration data obtained from the QCM, the mean effective density (ρeff) with uncertainty of inorganic salt particles (for particle count mean diameter (CMD) over a size range 10–478 nm), i.e. AS, SC and AN, is estimated to be 1.76 ± 0.24, 2.08 ± 0.19 and 1.69 ± 0.28 g cm−3, values which are comparable with the material density (ρ) values, 1.77, 2.17 and 1.72 g cm−3, respectively. Using this technique, the percentage contribution of error in the measurement of effective density is calculated to be in the range of 9–17 %. Among the individual uncertainty components, repeatability of particle mass obtained by the QCM, the QCM crystal frequency, CPC counting efficiency, and the equivalence of CPC- and QCM-derived volume are the major contributors to the expanded uncertainty (at k = 2) in comparison to other components, e.g. diffusion correction, charge correction, etc. Effective density for ambient particles at the beginning of the winter period in New Delhi was measured to be 1.28 ± 0.12 g cm−3. It was found that in general, mid-day effective density of ambient aerosols increases with increase in CMD of particle size measurement but particle photochemistry is an important factor to govern this trend. It is further observed that the CMD has good correlation with O3, SO2 and ambient RH, suggesting that possibly sulfate secondary materials have a substantial contribution in particle effective density. This approach can be useful for real-time measurement of effective density of both laboratory-generated and ambient aerosol particles, which is very important for studying the physico-chemical properties of particles.