Source contribution of black carbon aerosol during 2020-2022 at an urban site in Indo-Gangetic Plain.

The extensive emissions of black carbon (BC) from the Indo-Gangetic Plain (IGP) region of India have been well recognized. Particularly, biomass emissions from month-specific crop-residue burning (April, May, October, November) and heating activities (December-February) are considered substantial contributors to BC emissions in the IGP. However, their precise contribution to ambient BC aerosol has not been quantified yet and remains an issue of debate. Therefore, this study aims to fill this gap by quantifying the contribution of these month-specific biomass emissions to ambient BC at an urban site in IGP. This study presents the analysis of BC mass concentrations (MBC) measured for 3 years (2020-2022) in Delhi using an optical photometer i.e., continuous soot monitoring system (COSMOS). A statistical analysis of monthly mean MBC and factors affecting the MBC (ventilation coefficients, air mass back trajectories, fire counts) is performed to derive month-wise contribution due to background concentration, conventional emission, regional transport, crop-residue burning, and heating activities. The yearly mean MBC (5.3 ± 4.7, 5.6 ± 5.0, and 5.3 ± 3.5 µg m-3 during 2020, 2021, and 2022, respectively) remained relatively consistent with repetitive monthly patterns in each year. The peak concentrations were observed from November to January and low concentrations from June to September. Anthropogenic activities contributed significantly to MBC over Delhi with background concentration contributing only 30 % of observed MBC. The percentage contribution of emissions from crop-residue burning varied from 15 % (May) to 37 % (November), while the contribution from heating activities ranged from 25 % (December) to 39 % (January). This source quantification study highlights the significant impact of month-specific biomass emissions in the IGP and can play a vital role in better management and control of these emissions in the region.

Comparative measurement of CO2, CH4 and CO at two traffic interjunctions having inflated vehicular flow in Delhi.

Vehicular emissions are considered one of the major anthropogenic sources of greenhouse gases and poor air quality in metropolitan cities. This study aims to see the correlation of CO2, CH4, and CO through monitoring over a period from December 2020 to October 2021 covering three seasons' winter, summer, and monsoon at two different traffic locations of Delhi having different traffic volumes, road patterns, and traffic management. The annual average morning concentration of CO2, CH4 and CO was found (533 ± 105), (7.3 ± 3.1), (10.7 ± 3.0) ppm at Najafgarh and (480 ± 70), (5.2 ± 1.8), (7.8 ± 2.8) ppm at Rajendra Place, respectively. A relationship between concentration of all three gases and meteorological parameters such as temperature, humidity, wind speed and wind direction has also been investigated using Pearson correlation coefficient and pollution rose diagram. A comparable pattern in concentration was observed for all three gases in spatial (location) and temporal (diurnal) distribution. The concentration trend of CO2 in different seasons is winter > summer > monsoon, while in the case of CH4 winter = summer > monsoon but not any seasonal trend was noted in CO case. It is observed that CO2 has a good relation with CO (a tracer for vehicular emission) in terms of diurnal variation, whereas, CH4 does not represent a relation with CO and CO2 diurnally, suggesting that vehicles are the source of CO2 but not much contributing to other greenhouse gases like CH4.

Characterization of spatial-temporal distribution and microenvironment source contribution of PM2.5 concentrations using a low-cost sensor network with artificial neural network/kriging techniques.

Low-cost sensors (LCS) network is widely used to improve the resolution of spatial-temporal distribution of air pollutant concentrations in urban areas. However, studies on air pollution sources contribution to the microenvironment, especially in industrial and mix-used housing areas, still need to be completed. This study investigated the spatial-temporal distribution and source contributions of PM2.5 in the urban area based on 6-month of the LCS network datasets. The Artificial Neural Network (ANN) was used to calibrate the measured PM2.5 by the LCS network. The calibrated PM2.5 were shown to agree with reference PM2.5 measured by the BAM-1020 with R2 of 0.85, MNE of 30.91%, and RMSE of 3.73 µg/m3, which meet the criteria for hotspot identification and personal exposure study purposes. The Kriging method was further used to establish the spatial-temporal distribution of PM2.5 concentrations in the urban area. Results showed that the highest average PM2.5 concentration occurred during autumn and winter due to monsoon and topographic effects. From a diurnal perspective, the highest level of PM2.5 concentration was observed during the daytime due to heavy traffic emissions and industrial production. Based on the present ANN-based microenvironment source contribution assessment model, temples, fried chicken shops, traffic emissions in shopping and residential zones, and industrial activities such as the mechanical manufacturing and precision metal machining were identified as the sources of PM2.5. The numerical algorithm coupled with the LCS network presented in this study is a practical framework for PM2.5 hotspots and source identification, aiding decision-makers in reducing atmospheric PM2.5 concentrations and formulating regional air pollution control strategies.

Seasonal and diurnal measurement of ambient benzene at a high traffic inflation site in Delhi: Health risk assessment and its possible role in ozone formation pathways.

Benzene is the most toxic and hazardous pollutant among volatile organic compounds (VOCs), as it comes under group 1 carcinogens recognized by the International Agency for Research on Cancer (IARC). It also plays a significant role in forming secondary pollutants like ozone. The benzene concentration was measured using a charcoal sorbent tube by active sampling at a traffic junction and analysis was done using GC-FID. The maximum average concentration of benzene in ambient air was found to be 33 µg/m3. A diurnal study of benzene measurement shows higher benzene concentrations in the evening compared to the morning. Seasonal variation of benzene is found to be winter > spring > summer > autumn > monsoon and OFP was found to be 21, 19, 14, 13, and 10 respectively. Cancer (ILCR) and non-cancer (HQ) health risk assessment was done to determine the impact of ambient benzene on the residents of urban areas. The yearly average value of ILCR was found to be 2×10-6 ± 1×10-6 which ranges from acceptable value to three times the WHO acceptable value i.e 1×10-6. The correlation of ozone and its precursor, benzene with meteorological parameters is also evaluated. The correlation of benzene and ozone with solar radiation shows the influence of photochemical reactions on the levels of benzene and ozone at the study site, although it is low.

Physical and chemical properties of PM1 in Delhi: A comparison between clean and polluted days.

Considering the significance of PM1 aerosol in assessing health impacts of air pollution, an extensive analysis of PM1 samples collected at an urban site in Delhi is presented in this study. Overall, PM1 contributed to about 50 % of PM2.5 mass which is alarming especially in Delhi where particle mass loadings are usually higher than prescribed limits. Major portion of PM1 consisted of organic matter (OM) that formed nearly 47 % of PM1 mass. Elemental carbon (EC) contributed to about 13 % of PM1 mass, whereas SO42- (16 %), NH4+ (10 %), NO3- (4 %) and Cl- (3 %) were the major inorganic ions present. Sampling was performed in two distinctive campaign periods (in terms of meteorological conditions and heating (fire) activities), during the year 2019, each spanning two-week time, i.e. (i) September 3rd-16th (clean days), and (ii) November 22nd-December 5th (polluted days). Additionally, PM2.5 and black carbon (BC) were measured simultaneously for subsequent analysis. The 24-h averaged mean concentrations of PM2.5 and BC during clean days (polluted days) were 70.6 ± 26.9 and 3.9 ± 1.0 µg m-3 (196 ± 104 and 7.6 ± 4.1 µg m-3), respectively, which were systematically lower (higher) than that of the annual mean (taken from studies conducted at same site in 2019) of 142 and 5.7 µg m-3, respectively. Changes in characteristic ratios (i.e., organic carbon (OC)/elemental carbon (EC) and K+/EC) of chemical species detected in PM1 show an increase in biomass emissions during polluted days. Increase in biomass emission can be attributed to increase in heating practices (burning of biofuels such as wood logs, straw, and cow-dung cake) in- and around- Delhi because of fall in temperature during second campaign. Furthermore, a significant increase in NO3- fraction of PM1 is observed during second campaign which shows fog processing of NOX due to conducive meteorological conditions in winters. Also, comparatively stronger correlation of NO3- with K+ during second campaign (r = 0.98 as compared to r = 0.5 during first campaign) suggests the increased heating practices to be a contributing factor for increased fraction of NO3- in PM1. We observed that during polluted days, meteorological parameters such as dispersion rate also played a major role in intensifying the impact of increased local emissions due to heating activities. Apart from this, change in the direction of regional emission transport to study site and the topology of Delhi are the possible reasons for the elevated pollution level, especially PM1 during winter in Delhi. This study also suggests that black carbon measurement techniques used in current study (optical absorbance with heated inlet and evolved carbon techniques) can be used as reference techniques to determine the site-specific calibration constant of optical photometers for urban aerosol.

The influence of COVID-19 pandemic on PM2.5 air quality in Northern Taiwan from Q1 2020 to Q2 2021.

The study aimed to investigate the PM2.5 variations in different periods of COVID-19 control measures in Northern Taiwan from Quarter 1 (Q1) 2020 to Quarter 2 (Q2) 2021. PM2.5 sources were classified based on long-range transport (LRT) or local pollution (LP) in three study periods: one China lockdown (P1), and two restrictions in Taiwan (P2 and P3). During P1 the average PM2.5 concentrations from LRT (LRT-PM2.5-P1) were higher at Fuguei background station by 27.9% and in the range of 4.9-24.3% at other inland stations compared to before P1. The PM2.5 from LRT/LP mix or pure LP (Mix/LP-PM2.5-P1) was also higher by 14.2-39.9%. This increase was due to higher secondary particle formation represented by the increase in secondary ions (SI) and organic matter in PM2.5-P1 with the largest proportion of 42.17% in PM2.5 from positive matrix factorization (PMF) analysis. A similar increasing trend of Mix/LP-PM2.5 was found in P2 when China was still locked down and Taiwan was under an early control period but the rapidly increasing infected cases were confirmed. The shift of transportation patterns from public to private to avoid virus infection explicated the high correlation of the increasing infected cases with the increasing PM2.5. In contrast, the decreasing trend of LP-PM2.5-P3 was observed in P3 with the PM2.5 biases of ∼45% at all the stations when China was not locked down but Taiwan implemented a semi-lockdown. The contribution of gasoline vehicle sources in PM2.5 was reduced from 20.3% before P3 to 10% in P3 by chemical signatures and source identification using PMF implying the strong impact of strict control measures on vehicle emissions. In summary, PM2.5 concentrations in Northern Taiwan were either increased (P1 and P2) or decreased (P3) during the COVID-19 pandemic depending on control measures, source patterns and meteorological conditions.

On the techniques and standards of particulate matter sampling.

Air pollution and its limits are regulated by the environmental protection agency of an individual country according to their National Ambient Air Quality Standards (NAAQS). Particulate matter (e.g., TSP, PM10, and PM2.5) is one of the important criteria pollutants of NAAQS. Their measurement methods are specified in NAAQS, and detailed technical descriptions are given in standards. This review focuses on the sampling and analysis techniques and methods in the context of PM samplers' design mentioned in countries specific PM measuring standards (e.g., EPA Part 50, CEN 12341, IS 5182(23), etc.) and their comparison wherever is necessary. It discusses, different designs of PM samplers mentioned in standards and its important components, e.g., size fractionators cutoff efficiency, PM sampler head design, flow measurement, and calibration, and also addresses the important issues that are the limitation of present standards. Our review reveals that most of the country-specific standards show common practice in measuring PM2.5 using WINS impactor and VSCC cyclone as mentioned in EPA Part 50, except European Union (EU) standards, which has different design and parameters. For PM10 measurement, sampler design is different in EU and Indian standards than that of U.S. EPA and other countries' standards, which is discussed in length here. All standards lack in pointing some inherent problems like change in D50 cutoff of size fractionator of sampler under a high particle mass loading condition, which is common in countries like China and India. Other important issues where most of the standards lack include PM head design and specification, a key component of PM sampler on which the mass measurement results are largely dependent.Implications: The review paper discusses the air quality standards compliances of different countries and their comparisons. It focuses on the sampling and analysis techniques in context of PM samplers' design mentioned in countries specific PM measuring standards, and also addresses the important issues that are not mentioned in standards. Therefore, the discussions and findings of the review may be very useful while revising the existing air quality standards of different countries and to fill the research gap in this domain. Further, we have discussed several technical issues described in standards related to PM sampling which may be very helpful for PM sampler designing or modification in current designs as per the prevailing ambient conditions of a country.

Size distributions of n-alkanes, fatty acids and fatty alcohols in springtime aerosols from New Delhi, India.

Size-segregated aerosol samples were collected in New Delhi, India from March 6 to April 6, 2012. Homologous series of n-alkanes (C19C33), n-fatty acids (C12C30) and n-alcohols (C16C32) were measured using gas chromatography/mass spectrometry. Results showed a high-variation in the concentrations and size distributions of these chemicals during non-haze, haze, and dust storm days. In general, n-alkanes, n-fatty acids and n-alcohols presented a bimodal distribution, peaking at 0.7-1.1 µm and 4.7-5.8 µm for fine modes and coarse modes, respectively. Overall, the particulate matter mainly existed in the coarse mode (≥2.1 µm), accounting for 64.8-68.5% of total aerosol mass. During the haze period, large-scale biomass burning emitted substantial fine hydrophilic smoke particles into the atmosphere, which leads to relatively larger GMDs (geometric mean diameter) of n-alkanes in the fine mode than those during the dust storms and non-haze periods. Additionally, the springtime dust storms transported a large quantity of coarse particles from surrounding or local areas into the atmosphere, enhancing organic aerosol concentration and inducing a remarkable size shift towards the coarse mode, which are consistent with the larger GMDs of most organic compounds especially in total and coarse modes. Our results suggest that fossil fuel combustion (e.g., vehicular and industrial exhaust), biomass burning, residential cooking, and microbial activities could be the major sources of lipid compounds in the urban atmosphere in New Delhi.

Molecular Markers of Secondary Organic Aerosol in Mumbai, India.

Biogenic secondary organic aerosols (SOA) are generally considered to be more abundant in summer than in winter. Here, polar organic marker compounds in urban background aerosols from Mumbai were measured using gas chromatography-mass spectrometry. Surprisingly, we found that concentrations of biogenic SOA tracers at Mumbai were several times lower in summer (8-14 June 2006; wet season; n = 14) than in winter (13-18 February 2007; dry season; n = 10). Although samples from less than 10% of the season are extrapolated to the full season, such seasonality may be explained by the predominance of the southwest summer monsoon, which brings clean marine air masses to Mumbai. While heavy rains are an important contributor to aerosol removal during the monsoon season, meteorological data (relative humidity and T) suggest no heavy rains occurred during our sampling period. However, in winter, high levels of SOA and their day/night differences suggest significant contributions of continental aerosols through long-range transport together with local sources. The winter/summer pattern of SOA loadings was further supported by results from chemical transport models (NAQPMS and GEOS-Chem). Furthermore, our study suggests that monoterpene- and sesquiterpene-derived secondary organic carbon (SOC) were more significant than those of isoprene- and toluene-SOC at Mumbai.

Comparison of abundances, compositions and sources of elements, inorganic ions and organic compounds in atmospheric aerosols from Xi'an and New Delhi, two megacities in China and India.

Wintertime TSP samples collected in the two megacities of Xi'an, China and New Delhi, India were analyzed for elements, inorganic ions, carbonaceous species and organic compounds to investigate the differences in chemical compositions and sources of organic aerosols. The current work is the first time comparing the composition of urban organic aerosols from China and India and discussing their sources in a single study. Our results showed that the concentrations of Ca, Fe, Ti, inorganic ions, EC, PAHs and hopanes in Xi'an are 1.3-2.9 times of those in New Delhi, which is ascribed to the higher emissions of dust and coal burning in Xi'an. In contrast, Cl(-), levoglucosan, n-alkanes, fatty alcohols, fatty acids, phthalates and bisphenol A are 0.4-3.0 times higher in New Delhi than in Xi'an, which is attributed to strong emissions from biomass burning and solid waste incineration. PAHs are carcinogenic while phthalates and bisphenol A are endocrine disrupting. Thus, the significant difference in chemical compositions of the above TSP samples may suggest that residents in Xi'an and New Delhi are exposed to environmental hazards that pose different health risks. Lower mass ratios of octadecenoic acid/octadecanoic acid (C18:1/C18:0) and benzo(a)pyrene/benzo(e)pyrene (BaP/BeP) demonstrate that aerosol particles in New Delhi are photochemically more aged. Mass closure reconstructions of the wintertime TSP indicate that crustal material is the most abundant component of ambient particles in Xi'an and New Delhi, accounting for 52% and 48% of the particle masses, respectively, followed by organic matter (24% and 23% in Xi'an and New Delhi, respectively) and secondary inorganic ions (sulfate, nitrate plus ammonium, 16% and 12% in Xi'an and New Delhi, respectively).

Quantification of ziram and zineb residues in fog-water samples.

The present paper describes the extractive quantification of zinc-dithiocarbamate fungicides, i.e. ziram (zinc bis-dimethyldithiocarbamate) and zineb (zinc ethylene-1,2-bis-dithiocarbamate) in fog-water samples. The method is based on the releasing of equivalent amount of zinc from the fungicides and its subsequent determination by visible spectrophotometry or by flame-atomic absorption spectrometry (flame-AAS). For spectrophotometry, the sample contained up to 48mug of ziram and 42mug of zineb was first equilibrated with chloroform. The recovery results show that only ziram content was extracted into chloroform. Then, the sample was treated with NH(4)SCN and surfactants (i.e. CPC and TX-100) solutions, and extracted with toluene to remove interference of inorganic zinc and other metal ions, if present in the sample. The residue was further used for zineb determination. The chloroform extract and residue were then digested separately with nitric acid to release Zn(II), which were then analyzed spectrophotometerically with 4-(2-pyridylazo)-resorcinol in the micellar medium (TX-100) for the determination of ziram and zineb, respectively. The complex shows lambda(max) at 495nm. The molar absorptivity in terms of ziram/zineb was determined to be (8.05) x 10(4)Lmole(-1)cm(-1). The detection limits for ziram and zineb were calculated to be 20 and 21mugL(-1) (with R.S.D. < 1.5%), respectively. Whereas, the optimum concentration ranges were 0.08-1.6 and 0.07-1.4mgL(-1), respectively. Alternatively, the Zn contents present in chloroform extract and in residue were directly analyzed using flame-AAS without undergoing the digestion procedure, and ziram and zineb were determined, respectively. The optimum concentration ranges were 0.9-4.8 and 0.8-4.3mgL(-1), while the detection limits were calculated to be 145 and 144mugL(-1), respectively with R.S.D. < 2.5%. The methods are free from interference of almost all ions [including Zn(II)] and other dithiocarbamate pesticides, which can commonly associate with ziram/zineb in fog-water.

Efficient control system for low-concentration inorganic gases from a process vent stream: application of surfactants in spray and packed columns.

Control of low-concentration pollutants from a semiconductor process vent stream using a wet-scrubbing technique is a challenging task to meet Taiwan environmental emission standards. An efficient wet-scrubber is designed on a pilot scale and tested to control low concentration acid and base waste-gas emission. The scrubber system consisted of two columns, i.e., a fine spray column [cutoff diameter (based on volume), Dv(50) = 15.63 microm; Sauter mean diameter (SMD) = 7.62 microm], which is especially efficient for NH3 removal as the pH of the spraying liquid is approximately 7 followed by a packed column with a scrubbing liquid pH approximately 9.0 mainly for acids removal. It is observed that use of the surfactants in low concentration about 10(-4) M and 10(-7) M in the spray liquid and in the scrubbing liquid, respectively, remarkably enhances the removal efficiency of the system. A traditional packed column (without the spray column and the surfactant) showed that the removal efficiencies of NH3, HF, and HCl for the inlet concentration range 0.2 to 3 ppm were (n = 5) 22.6+/-3.4%, 43.4+/-5.5%, and 40.4+/-7.4%, respectively. The overall efficiencies of the proposed system (the spray column and the packed column) in the presence of the surfactant in the spray liquid and in the scrubbing liquid forthese three species were found to increase significantly (n = 5) from 60.3+/-3.6 to 82.8+/-6.8%, 59.1+/-2.7 to 83.4+/-4.2%, and 56.2+/-7.3 to 81.0+/-6.7%, respectively. In this work, development of charge on the gas-liquid interface due to the surfactants has been measured and discussed. It is concluded that the presence of charge on the gas-liquid interface is the responsible factor for enhancement of the removal efficiency (mass-transfer in liquid phase). The effects of the type of surfactants, their chain length, concentration in liquid, etc. on the removal efficiency are discussed. Since the pilot tests were performed under the operating conditions similar to most of the wet-scrubbers operated in semiconductors manufacturing facilities for inorganic pollutants, this study can be applied to modify the existing wet-scrubbers to enhance the removal efficiencies, especially for low-concentration pollutants.

Simultaneous sampling of gas- and aerosol-phase TDI with a triple filter system.

A new triple filter system sampler/model is proposed for the precise and accurate simultaneous sampling and determination of gas- and aerosol-phase 2,4-toluene diisocyanate (TDI). The system consists of two front Teflon filters for sampling aerosol-phase TDI and a final coated glass fiber filter to collect gas-phase TDI. The aerosol-phase TDI is collected on the first Teflon filter, while the second Teflon filter is used to estimate gaseous TDI adsorbed by the first. According to the gas adsorption test of two Teflon filters in series, the TDI gas adsorption fraction of the two filters is almost the same. Results of the evaporation test using pure TDI aerosols collected on the Teflon filter show that significant evaporation of the compound does not occur during sampling. These two findings allow the use of a model to estimate accurate gas- and aerosol-phase TDI concentrations. The comparison test with an annular denuder shows that the triple filter system can minimize the TDI sampling bias between the dual filter and the annular denuder systems.

Specific determination of ferbam residues in fog-water.

A specific method for the determination of a fungicide, i.e. iron(III) dimethyldithiocarbamate (ferbam) in fog-water samples is described. The method is based on the releasing of equivalent amount of iron from the fungicide and subsequently determination by spectrophotometrically or by flame-atomic absorption spectrometrically (flame-AAS). The fungicide was extracted with chloroform/toluene from the samples and digested with nitric acid. For spectrophotometric determination, the solution was then treated with ammonium thiocyanate solution in presence of the surfactants and absorbance was measured at 475 nm. Whereas, the digested solution was directly applied for flame-AAS determination of ferbam. The molar absorptivity in terms of ferbam was determined to be (3.49)x10(4) l mol(-1) cm(-1). The detection limits for spectrophotometric and flame-AAS methods were calculated to be 62 and 111 ppb ferbam (R.S.D. <1 and <3%), respectively. Whereas, the optimum concentration ranges for the analysis of ferbam are 4-120 and 1.5-55 mug in final volume, respectively. The methods are freed from interference of almost all ions [including Fe(II) and Fe(III)], which can commonly associate with ferbam in fog-water. The methods have been successfully applied to fog samples collected from agriculture sites of Raipur (central India).

The effect of environmental conditions and electrical charge on the weighing accuracy of different filter materials.

Different filter materials and electrical charge elimination methods were used to investigate the weighing accuracy of filter papers under different environmental conditions. The results show that the standard deviations (S.D.) of weight data for glass fiber and MCE filters were substantial without environmental control, whether or not the electrical charge eliminators were used. Values of 0.157 and 0.349 mg were determined for glass and MCE filters, respectively. The accuracy of weighing was substantially improved and the S.D. was reduced to 0.01 and 0.09 mg for glass fiber and MCE filters, respectively, after applying the environmental control conditions. For PVC and Teflon filters, the accuracy of weighing was good, even in the uncontrolled environmental conditions, whether or not the electrical charge eliminators were used. The S.D. values of weighing data of PVC and Teflon filters were 0.007 and 0.011 mg, respectively.