Delhi, India, routinely experiences some of the world's highest urban
particulate matter concentrations. We established the Delhi Aerosol Supersite
study to provide long-term
characterization of the ...ambient submicron aerosol composition in Delhi. Here
we report on 1.25 years of highly time-resolved speciated submicron
particulate matter (PM1) data, including black carbon (BC) and
nonrefractory PM1 (NR-PM1), which we combine to develop a
composition-based estimate of PM1
(“C-PM1” = BC + NR-PM1) concentrations. We observed marked seasonal and diurnal variability in the concentration and
composition of PM1 owing to the interactions of sources and atmospheric
processes. Winter was the most polluted period of the year, with average
C-PM1 mass concentrations of ∼210 µg m−3. The monsoon was hot and rainy, consequently
making it the least polluted (C-PM1 ∼50 µg m−3) period. Organics constituted more than half
of the C-PM1 for all seasons and times of day. While ammonium, chloride,
and nitrate each were ∼10 % of the C-PM1 for the cooler
months, BC and sulfate contributed ∼5 % each. For the warmer
periods, the fractional contribution of BC and sulfate to C-PM1
increased, and the chloride contribution decreased to less than 2 %. The
seasonal and diurnal variation in absolute mass loadings were generally
consistent with changes in ventilation coefficients, with higher
concentrations for periods with unfavorable meteorology – low
planetary boundary layer height and low wind speeds. However, the variation
in C-PM1 composition was influenced by temporally varying sources,
photochemistry, and gas–particle partitioning. During cool periods when wind
was from the northwest, episodic hourly averaged chloride concentrations
reached 50–100 µg m−3, ranking
among the highest chloride concentrations reported anywhere in the world. We estimated the contribution of primary emissions and secondary processes to
Delhi's submicron aerosol. Secondary species contributed
almost 50 %–70 % of Delhi's C-PM1 mass for the
winter and spring months and up to 60 %–80 % for the warmer summer
and monsoon months. For the cooler months that had the highest C-PM1
concentrations, the nighttime sources were skewed towards primary sources,
while the daytime C-PM1 was dominated by secondary species. Overall,
these findings point to the important effects of both primary emissions and
more regional atmospheric chemistry on influencing the extreme particle
concentrations that impact the Delhi megacity region. Future air quality
strategies considering Delhi's situation in both a regional
and local context will be more effective than policies targeting only local,
primary air pollutants.
All conventional hygroscopicity parameter (κ) estimates are based on ammonium salts being the dominant salts, besides sea salt at marine locations. This grossly underestimates κ for highly polluted ...cities like New Delhi which is subjected to high mineral dust. To validate this hypothesis, the impact of mineral dust on κ was quantified following two mathematical approaches based on Mann-Kendall's test which differed in the sequence followed for compound formation. This leads to a remarkably high increment in κ, on an average of 57% and 63.5% during the day and night respectively, for the period Dec 2012–2014 and is based on the detailed chemical speciation of PM2.5 data. The inter-comparison of κ obtained from various analytical methods challenge the traditional way of estimating κ by including the chemical composition of a few dominant species and ignoring the others without paying any heed to the dependence of κ on Temperature (T) and Relative Humidity (RH). An increase in the ratio of water-soluble organic carbon to organic carbon lessened the impact of mineral dust on κ. The insolubility of calcium salts also decreased the effect of mineral dust, but at the same time lead to MgCl2 formation which augmented the estimated κ. The highest obtained κ was 0.82 (on 23/7/2014 during the night). The impact of mineral dust was also found to be significant for two other Indian (Durg and Kanpur) and Chinese (Xian and Beijing) cities for both PM1 and PM2.5 regimes. The high value of κ and impact of mineral dust on κ can be crucial in Cloud Condensation Nuclei (CCN) estimation at polluted sites subjected to mineral dust and thus impact precipitation quantification by Global Climatic models (GCMs), lead to visibility deterioration and affect the indirect radiative forcing.
•Ignoring mineral dust in dust-influenced regions can under-estimate the hygroscopicity parameter (κ) significantly.•Impact of composition > Relative Humidity (RH) > Temperature (T) on κ for small variations in RH and T.•Large variations in RH may impact κ comparable to chemical composition.•The sequence of compound formation is an important criterion impacting κ that requires a thorough investigation.•An increase in the presence of water-soluble organic carbon and insoluble calcium salts diminishes the mineral dust impact.
Delhi is a megacity subject to high local anthropogenic emissions and long-range transport of pollutants. This work presents for the first time time-resolved estimates of hygroscopicity parameter (κ) ...and cloud condensation nuclei (CCN), spanning for more than a year, derived from chemical composition and size distribution data. As a part of the Delhi Aerosol Supersite (DAS) campaign, the characterization of aerosol composition and size distribution was conducted from January 2017 to March 2018. Air masses originating from the Arabian Sea (AS), Bay of Bengal (BB), and southern Asia (SA) exhibited distinct characteristics of time-resolved sub-micron non-refractory PM1 (NRPM1) species, size distributions, and CCN number concentrations. The SA air mass had the highest NRPM1 loading with high chloride and organics, followed by the BB air mass, which was more contaminated than AS, with a higher organic fraction and nitrate. The primary sources were identified as biomass-burning, thermal power plant emissions, industrial emissions, and vehicular emissions. The average hygroscopicity parameter (κ), calculated by the mixing rule, was approximately 0.3 (varying between 0.13 and 0.77) for all the air masses (0.32±0.06 for AS, 0.31±0.06 for BB, and 0.32±0.10 for SA). The diurnal variations in κ were impacted by the chemical properties and thus source activities. The total, Aitken, and accumulation mode number concentrations were higher for SA, followed by BB and AS. The mean values of estimated CCN number concentration (NCCN; 3669–28926 cm−3) and the activated fraction (af; 0.19–0.87), for supersaturations varying from 0.1 % to 0.8 %, also showed the same trend, implying that these were highest in SA, followed by those in BB and then those in AS. The size turned out to be more important than chemical composition directly, and the NCCN was governed by either the Aitken or accumulation modes, depending upon the supersaturation (SS) and critical diameter (Dc). af was governed mainly by the geometric mean diameter (GMD), and such a high af (0.71±0.14 for the most dominant sub-branch of the SA air mass – R1 – at 0.4 % SS) has not been seen anywhere in the world for a continental site. The high af was a consequence of very low Dc (25–130 nm, for SS ranging from 0.1 % to 0.8 %) observed for Delhi. Indirectly, the chemical properties also impacted CCN and af by impacting the diurnal patterns of Aitken and accumulation modes, κ and Dc. The high-hygroscopic nature of aerosols, high NCCN, and high af can severely impact the precipitation patterns of the Indian monsoon in Delhi, impact the radiation budget, and have indirect effects and need to be investigated to quantify this impact.
Delhi, India, is the second most populated city in the world and routinely experiences some of the highest particulate matter concentrations of any megacity on the planet, posing acute challenges to ...public health (World Health Organization, 2018). However, the current understanding of the sources and dynamics of PM pollution in Delhi is limited. Measurements at the Delhi Aerosol Supersite (DAS) provide long-term chemical characterization of ambient submicron aerosol in Delhi, with near-continuous online measurements of aerosol composition. Here we report on source apportionment based on positive matrix factorization (PMF), conducted on 15 months of highly time-resolved speciated submicron non-refractory PM1 (NR-PM1) between January 2017 and March 2018. We report on seasonal variability across four seasons of 2017 and interannual variability using data from the two winters and springs of 2017 and 2018. We show that a modified tracer-based organic component analysis provides an opportunity for a real-time source apportionment approach for organics in Delhi. Phase equilibrium modeling of aerosols using the extended aerosol inorganics model (E-AIM) predicts equilibrium gas-phase concentrations and allows evaluation of the importance of the ventilation coefficient (VC) and temperature in controlling primary and secondary organic aerosol. We also find that primary aerosol dominates severe air pollution episodes, and secondary aerosol dominates seasonal averages.
The Indian national capital, Delhi, routinely experiences some of the world's highest urban particulate matter concentrations. While fine particulate matter (PM2.5) mass concentrations in Delhi are ...at least an order of magnitude higher than in many western cities, the particle number (PN) concentrations are not similarly elevated. Here we report on 1.25 years of highly time-resolved particle size distribution (PSD) data in the size range of 12–560 nm. We observed that the large number of accumulation mode particles – that constitute most of the PM2.5 mass – also contributed substantially to the PN concentrations. The ultrafine particle (UFP; Dp<100 nm) fraction of PNs was higher during the traffic rush hours and for daytimes of warmer seasons, which is consistent with traffic and nucleation events being major sources of urban UFPs. UFP concentrations were found to be relatively lower during periods with some of the highest mass concentrations. Calculations based on measured PSDs and coagulation theory suggest UFP concentrations are suppressed by a rapid coagulation sink during polluted periods when large concentrations of particles in the accumulation mode result in high surface area concentrations. A smaller accumulation mode for warmer months results in an increased UFP fraction, likely owing to a comparatively smaller coagulation sink. We also see evidence suggestive of nucleation which may also contribute to the increased UFP proportions during the warmer seasons. Even though coagulation does not affect mass concentrations, it can significantly govern PN levels with important health and policy implications. Implications of a strong accumulation mode coagulation sink for future air quality control efforts in Delhi are that a reduction in mass concentration, especially in winter, may not produce a proportional reduction in PN concentrations. Strategies that only target accumulation mode particles (which constitute much of the fine PM2.5 mass) may even lead to an increase in the UFP concentrations as the coagulation sink decreases.
Delhi, India, experiences extremely high concentrations of primary organic aerosol (POA). Few prior source apportionment studies on Delhi have captured the influence of biomass burning organic ...aerosol (BBOA) and cooking organic aerosol (COA) on POA. In a companion paper, we develop a new method to conduct source apportionment resolved by time of day using the underlying approach of positive matrix factorization (PMF). We call this approach "time-of-day PMF" and statistically demonstrate the improvements of this approach over traditional PMF. Here, we quantify the contributions of BBOA, COA, and hydrocarbon-like organic aerosol (HOA) by applying positive matrix factorization (PMF) resolved by time of day on two seasons (winter and monsoon seasons of 2017) using organic aerosol measurements from an aerosol chemical speciation monitor (ACSM). We deploy the EPA PMF tool with the underlying Multilinear Engine (ME-2) as the PMF solver. We also conduct detailed uncertainty analysis for statistical validation of our results.
Present methodologies for source apportionment assume fixed source profiles. Since meteorology and human activity patterns change seasonally and diurnally, application of source apportionment ...techniques to shorter rather than longer time periods generates more representative mass spectra. Here, we present a new method to conduct source apportionment resolved by time of day using the underlying approach of positive matrix factorization (PMF). We call this approach “time-of-day PMF” and statistically demonstrate the improvements in this approach over traditional PMF. We report on source apportionment conducted on four example time periods in two seasons (winter and monsoon seasons of 2017), using organic aerosol measurements from an aerosol chemical speciation monitor (ACSM). We deploy the EPA PMF tool with the underlying Multilinear Engine (ME-2) as the PMF solver. Compared to the traditional seasonal PMF approach, we extract a larger number of factors as well as PMF factors that represent the expected sources of primary organic aerosol using time-of-day PMF. By capturing diurnal time series patterns of sources at a low computational cost, time-of-day PMF can utilize large datasets collected using long-term monitoring and improve the characterization of sources of organic aerosol compared to traditional PMF approaches that do not resolve by time of day.
ABSTRACT Objective: To determine medical and dental students' eating habits and knowledge of nutritional requirements for health. Study Design: A cross-sectional analytical study. Place and Duration ...of Study: Conducted at CMH Lahore Medical College and Institute of Dentistry (CMH LMC and IOD), from Jun to Nov 2019. Methodology: A total of 142 students of first year of MBBS and BDS of CMH Lahore Medical College and Institute of Dentistry fulfilling the inclusion criteria were given a self-administered survey questionnaire consisting of demographic details, dietary habits and dietary knowledge. Data was analyzed through SPSS 21. Results: Majority of participants (75, 52.8%) were females and aged less than 22 years (78.2%). Most of them (73, 51.4%) were hostelite and 82 (57.7%) had normal body mass index (BMI). Most participants exhibited good knowledge of nutrition. 89 (62.7%) consumed fast food once or twice a week and 31 (21.8%) took fast food daily. There was no significant difference among the genders or among hostelites and day scholars with respect to most of the identified dietary habits. However, male students drank more soda, but ate more fresh fruits than the female students. Also, hostelites were found to be more prone to eat unhealthy foods when stressed as compared to the day scholars. Conclusion: Most of the students had adequate dietary knowledge. High rates of fast food consumption imply the need for increased awareness of links between health and nutrition in these students.
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