scholarly journals Size distribution of alkyl amines in continental particulate matter and their online detection in the gas and particle phase

2011 ◽  
Vol 11 (9) ◽  
pp. 4319-4332 ◽  
Author(s):  
T. C. VandenBoer ◽  
A. Petroff ◽  
M. Z. Markovic ◽  
J. G. Murphy
Keyword(s):  
Particulate Matter ◽  
Detection Limit ◽  
Gas Phase ◽  
Size Dependence ◽  
Fine Particulate Matter ◽  
Molar Ratio ◽  
Ambient Atmosphere ◽  
Good Resolution ◽  
Particle Phase ◽  
Alkyl Amines

Abstract. An ion chromatographic method is described for the quantification of the simple alkyl amines: methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), ethylamine (EA), diethylamine (DEA) and triethylamine (TEA), in the ambient atmosphere. Limits of detection (3σ) are in the tens of pmol range for all of these amines, and good resolution is achieved for all compounds except for TMA and DEA. The technique was applied to the analysis of time-integrated samples collected using a micro-orifice uniform deposition impactor (MOUDI) with ten stages for size resolution of particles with aerodynamic diameters between 56 nm and 18 μm. In eight samples from urban and rural continental airmasses, the mass loading of amines consistently maximized on the stage corresponding to particles with aerodynamic diameters between 320 and 560 nm. The molar ratio of amines to ammonium (R3NH+/NH4+) in fine aerosol ranged between 0.005 and 0.2, and maximized for the smallest particle sizes. The size-dependence of the R3NH+/NH4+ ratio indicates differences in the relative importance of the processes leading to the incorporation of amines and ammonia into secondary particles. The technique was also used to make simultaneous hourly online measurements of amines in the gas phase and in fine particulate matter using an Ambient Ion Monitor Ion Chromatograph (AIM-IC). During a ten day campaign in downtown Toronto, DMA, TMA + DEA, and TEA were observed to range from below detection limit to 2.7 ppt in the gas phase. In the particle phase, MAH+ and TMAH+ + DEAH+ were observed to range from below detection limit up to 15 ng m−3. The presence of detectable levels of amines in the particle phase corresponded to periods with higher relative humidity and higher mass loadings of nitrate. While the hourly measurements made using the AIM-IC provide data that can be used to evaluate the application of gas-particle partitioning models to amines, the strong size-dependence of the R3NH+/NH4+ ratio indicates that using bulk measurements may not be appropriate.

scholarly journals Size distribution of alkyl amines in continental particulate matter and their online detection in the gas and particle phase

2010 ◽  
Vol 10 (11) ◽  
pp. 27435-27477
Author(s):  
T. C. VandenBoer ◽  
A. Petroff ◽  
M. Z. Markovic ◽  
J. G. Murphy
Keyword(s):  
Particulate Matter ◽  
Detection Limit ◽  
Gas Phase ◽  
Size Dependence ◽  
Fine Particulate Matter ◽  
Molar Ratio ◽  
Ambient Atmosphere ◽  
Good Resolution ◽  
Particle Phase ◽  
Alkyl Amines

Abstract. An ion chromatographic method is described for the quantification of the simple alkyl amines: methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), ethylamine (EA), diethylamine (DEA) and triethylamine (TEA), in the ambient atmosphere. Limits of detection (3σ) are in the tens of pmol range for all of these amines, and good resolution is achieved for all compounds except for TMA and DEA. The technique was applied to the analysis of time-integrated samples collected using a micro-orifice uniform deposition impactor (MOUDI) with ten stages for size resolution of particles with aerodynamic diameters between 56 nm and 18 μm. In eight samples from urban and rural continental airmasses, the mass loading of amines consistently maximized on the stage corresponding to particles with aerodynamic diameters between 320 and 560 nm. The molar ratio of amines to ammonium (R3NH+/NH4+) in fine aerosol ranged between 0.005 and 0.2, and maximized for the smallest particle sizes. The size-dependence of the R3NH+/NH4+ ratio indicates differences in the relative importance of the processes leading to the incorporation of amines and ammonia into secondary particles. The technique was also used to make simultaneous hourly online measurements of amines in the gas phase and in fine particulate matter using an Ambient Ion Monitor Ion Chromatograph (AIM-IC). During a ten day campaign in downtown Toronto, DMA, TMA+DEA, and TEA were observed to range from below detection limit to 2.7 ppt in the gas phase. In the particle phase, MAH+ and TMAH++DEAH+ were observed to range from below detection limit up to 15 ng m−3. The presence of detectable levels of amines in the particle phase corresponded to periods with higher relative humidity and higher mass loadings of nitrate. While the hourly measurements made using the AIM-IC provide data that can be used the evaluate the application of gas-particle partitioning models to amines, the strong size-dependence of the R3NH+/NH4+ ratio indicates that using bulk measurements and an assumption of internal mixing may not be appropriate.

scholarly journals Local and regional contributions to fine particulate matter in the 18 cities of Sichuan Basin, southwestern China

2019 ◽  
Vol 19 (9) ◽  
pp. 5791-5803 ◽  
Author(s):  
Xue Qiao ◽  
Hao Guo ◽  
Ya Tang ◽  
Pengfei Wang ◽  
Wenye Deng ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Gas Phase ◽  
Sichuan Basin ◽  
Fine Particulate Matter ◽  
Eastern China ◽  
Northern China ◽  
Sulfate Ions ◽  
Inorganic Aerosols ◽  
Fine Particulate ◽  
The Sichuan Basin

Abstract. The Sichuan Basin (SCB) is one of the regions suffering from severe air pollution in China, but fewer studies have been conducted for this region than for the more developed regions in eastern and northern China. In this study, a source-oriented version of the Community Multiscale Air Quality (CMAQ) model was used to quantify contributions from nine regions to PM2.5 (i.e., particulate matter, PM, with an aerodynamic diameter less than 2.5 µm) and its components in the 18 cities within the SCB in the winter (December  2014 to February 2015) and summer (June to August 2015). In the winter, citywide average PM2.5 concentrations are 45–126 µg m−3, with 21 %–51 % and 39 %–66 % being due to local and nonlocal emissions, respectively. In the summer, 15 %–45 % and 25 %–52 % of citywide average PM2.5 (14–31 µg m−3) are due to local and nonlocal emissions, respectively. Compared to primary PM (PPM), the inter-region transport of secondary inorganic aerosols (SIA), including ammonia, nitrate, and sulfate ions (NH4+, NO3-, and SO42-, respectively), and their gas-phase precursors are greater. The region to the east of SCB (R7, including central and eastern China and others) is the largest contributor outside the SCB, and it can contribute approximately 80 % of PM2.5 in the eastern, northeastern, and southeastern rims of the SCB but only 10 % in other SCB regions in both seasons. Under favorable transport conditions, regional transport of air pollutants from R7 could account for up to 35–100 µg m−3 of PM2.5 in each of the SCB cities in the winter. This study demonstrates that it is important to have joint emission control efforts among cities within the SCB and regions to the east in order to reduce PM2.5 concentrations and prevent high PM2.5 days for the entire basin.

scholarly journals Modeling reactive ammonia uptake by secondary organic aerosol in CMAQ: application to the continental US

2018 ◽  
Vol 18 (5) ◽  
pp. 3641-3657 ◽  
Author(s):  
Shupeng Zhu ◽  
Jeremy R. Horne ◽  
Julia Montoya-Aguilera ◽  
Mallory L. Hinks ◽  
Sergey A. Nizkorodov ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Air Quality ◽  
Ammonium Nitrate ◽  
Gas Phase ◽  
Ammonium Sulfate ◽  
Fine Particulate Matter ◽  
Considerable Uncertainty ◽  
Ammonia Uptake ◽  
Different Seasons ◽  
Uptake Coefficients

Abstract. Ammonium salts such as ammonium nitrate and ammonium sulfate constitute an important fraction of the total fine particulate matter (PM2.5) mass. While the conversion of inorganic gases into particulate-phase sulfate, nitrate, and ammonium is now well understood, there is considerable uncertainty over interactions between gas-phase ammonia and secondary organic aerosols (SOAs). Observations have confirmed that ammonia can react with carbonyl compounds in SOA, forming nitrogen-containing organic compounds (NOCs). This chemistry consumes gas-phase NH3 and may therefore affect the amount of ammonium nitrate and ammonium sulfate in particulate matter (PM) as well as particle acidity. In order to investigate the importance of such reactions, a first-order loss rate for ammonia onto SOA was implemented into the Community Multiscale Air Quality (CMAQ) model based on the ammonia uptake coefficients reported in the literature. Simulations over the continental US were performed for the winter and summer of 2011 with a range of uptake coefficients (10−3–10−5). Simulation results indicate that a significant reduction in gas-phase ammonia may be possible due to its uptake onto SOA; domain-averaged ammonia concentrations decrease by 31.3 % in the winter and 67.0 % in the summer with the highest uptake coefficient (10−3). As a result, the concentration of particulate matter is also significantly affected, with a distinct spatial pattern over different seasons. PM concentrations decreased during the winter, largely due to the reduction in ammonium nitrate concentrations. On the other hand, PM concentrations increased during the summer due to increased biogenic SOA (BIOSOA) production resulting from enhanced acid-catalyzed uptake of isoprene-derived epoxides. Since ammonia emissions are expected to increase in the future, it is important to include NH3 + SOA chemistry in air quality models.

scholarly journals Modeling reactive ammonia uptake by secondary organic aerosol in CMAQ: application to continental US

2017 ◽  
Author(s):  
Shupeng Zhu ◽  
Jeremy R. Horne ◽  
Julia Montoya-Aguilera ◽  
Mallory L. Hinks ◽  
Sergey A. Nizkorodov ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Air Quality ◽  
Ammonium Nitrate ◽  
Gas Phase ◽  
Ammonium Sulfate ◽  
Fine Particulate Matter ◽  
Considerable Uncertainty ◽  
Ammonia Uptake ◽  
Different Seasons ◽  
Uptake Coefficients

Abstract. Ammonium salts such as ammonium nitrate and ammonium sulfate constitute an important fraction of the total fine particulate matter (PM2.5) mass. While the conversion of inorganic gases into particulate phase sulfate, nitrate, and ammonium is now well understood, there is considerable uncertainty over interactions between gas-phase ammonia and secondary organic aerosols (SOA). Observations have confirmed that ammonia can react with carbonyl compounds in SOA, forming nitrogen-containing organic compounds (NOC). This chemistry can reduce gas-phase NH3 concentration and therefore affect the amount of ammonium nitrate and ammonium sulfate in particulate matter (PM). In order to investigate the importance of such reactions, a first-order loss rate for ammonia onto SOA was implemented into the Community Multiscale Air Quality (CMAQ) model based on the ammonia uptake coefficients reported in the literature. Simulations over the continental US were performed for the winter and summer of 2011 with a range of uptake coefficients (10−3–10−5). Simulation results indicate that a significant reduction in gas-phase ammonia is possible due to its uptake onto SOA; domain-averaged ammonia concentrations decrease by 31.3 % in the winter, and 67.0 % in the summer with the highest uptake coefficient (10−3). As a result, the concentration of particulate matter is also significantly affected, with a distinct spatial pattern over different seasons. PM concentrations decreased during the winter, largely due to the reduction in ammonium nitrate concentrations. On the other hand, PM concentrations increased during the summer due to increased production of biogenic SOA production resulting from enhanced acid-catalyzed uptake of isoprene-derived epoxides. While ammonia emissions expected to increase in the future, it is important to include NH3 + SOA chemistry in air quality models.

scholarly journals The Role of Coarse Aerosol Particles as a Sink of HNO<sub>3</sub> in Wintertime Pollution Events in the Salt Lake Valley

2020 ◽  
Author(s):  
Amy Hrdina ◽  
Jennifer G. Murphy ◽  
Anna Gannet Hallar ◽  
John C. Lin ◽  
Alexander Moravek ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Gas Phase ◽  
Salt Lake ◽  
Fine Particulate Matter ◽  
The United States ◽  
Water Soluble ◽  
Salt Lake Valley ◽  
Fine Particulate ◽  
Coarse Mode ◽  
Pollution Events

Abstract. Wintertime ammonium nitrate (NH4NO3) pollution events burden urban mountain basins around the globe. In the Salt Lake Valley of Utah in the United States, such pollution events are often driven by the formation of persistent cold air pools (PCAP) that trap emissions near the surface for several consecutive days. As a result, secondary pollutants including fine particulate matter less than 2.5 μm in diameter (PM2.5), largely in the form of NH4NO3, build up during these events and lead to severe haze. As part of an extensive measurement campaign to understand the chemical processes underlying PM2.5 formation, the 2017 Utah Winter Fine Particulate Study, water-soluble trace gases and PM2.5 constituents were continuously monitored using the Ambient Ion Monitoring Ion Chromatograph system (AIM-IC) at the University of Utah campus. Gas phase NH3, HNO3, HCl and SO2 along with particulate NH4+, Na+, K+, Mg2+, Ca2+, NO3−, Cl−, and SO42− were measured from January 21 to February 21, 2017. During the two PCAP events captured, the fine particulate matter was dominated by secondary NH4NO3. The comparison of total nitrate (HNO3 + PM2.5 NO3−) and total NHx (NH3 + PM2.5 NH4+) showed NHx was in excess during both pollution events. However, chemical composition analysis of the snowpack during the first PCAP event revealed that the total concentration of deposited NO3− was nearly three times greater than that of deposited NH4+. Daily snow composition measurements showed a strong correlation between NO3− and Ca2+ in the snowpack. The presence of non-volatile salts (Na+, Ca2+, and Mg2+), which are frequently associated with coarse mode dust, was also detected in PM2.5 by the AIM-IC during the two PCAP events, accounting for roughly 5 % of total mass loading. The presence of a significant particle mass and surface area in the coarse mode during the first PCAP event was indicated by size-resolved particle measurements from an Aerodynamic Particle Sizer. Taken together, these observations imply that atmospheric measurements of the gas phase and fine mode particle nitrate may not represent the total burden of nitrate in the atmosphere, implying a potentially significant role for uptake by coarse mode dust. Using the NO3− : NH4+ ratio observed in the snowpack to estimate the proportion of atmospheric nitrate present in the coarse mode, we estimate that the amount of secondary NH4NO3 could double in the absence of the coarse mode sink. The underestimation of total nitrate indicates an incomplete account of the total oxidant production during PCAP events. The ability of coarse particles to permanently remove HNO3 and influence PM2.5 formation is discussed using information about particle composition and size distribution.

scholarly journals The role of coarse aerosol particles as a sink of HNO<sub>3</sub> in wintertime pollution events in the Salt Lake Valley

2021 ◽  
Vol 21 (10) ◽  
pp. 8111-8126
Author(s):  
Amy Hrdina ◽  
Jennifer G. Murphy ◽  
Anna Gannet Hallar ◽  
John C. Lin ◽  
Alexander Moravek ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Gas Phase ◽  
Salt Lake ◽  
Fine Particulate Matter ◽  
The United States ◽  
Water Soluble ◽  
Salt Lake Valley ◽  
Fine Particulate ◽  
Coarse Mode ◽  
Pollution Events

Abstract. Wintertime ammonium nitrate (NH4NO3) pollution events burden urban mountain basins around the globe. In the Salt Lake Valley of Utah in the United States, such pollution events are often driven by the formation of persistent cold-air pools (PCAPs) that trap emissions near the surface for several consecutive days. As a result, secondary pollutants including fine particulate matter less than 2.5 µm in diameter (PM2.5), largely in the form of NH4NO3, build up during these events and lead to severe haze. As part of an extensive measurement campaign to understand the chemical processes underlying PM2.5 formation, the 2017 Utah Winter Fine Particulate Study, water-soluble trace gases and PM2.5 constituents were continuously monitored using the ambient ion monitoring ion chromatograph (AIM-IC) system at the University of Utah campus. Gas-phase NH3, HNO3, HCl, and SO2 along with particulate NH4+, Na+, K+, Mg2+, Ca2+, NO3-, Cl−, and SO42- were measured from 21 January to 21 February 2017. During the two PCAP events captured, the fine particulate matter was dominated by secondary NH4NO3. The comparison of total nitrate (HNO3 + PM2.5 NO3-) and total NHx (NH3 + PM2.5 NH4+) showed NHx was in excess during both pollution events. However, chemical composition analysis of the snowpack during the first PCAP event revealed that the total concentration of deposited NO3- was nearly 3 times greater than that of deposited NH4+. Daily snow composition measurements showed a strong correlation between NO3- and Ca2+ in the snowpack. The presence of non-volatile salts (Na+, Ca2+, and Mg2+), which are frequently associated with coarse-mode dust, was also detected in PM2.5 by the AIM-IC during the two PCAP events, accounting for roughly 5 % of total mass loading. The presence of a significant particle mass and surface area in the coarse mode during the first PCAP event was indicated by size-resolved particle measurements from an aerodynamic particle sizer. Taken together, these observations imply that atmospheric measurements of the gas-phase and fine-mode particle nitrate may not represent the total burden of nitrate in the atmosphere, implying a potentially significant role for uptake by coarse-mode dust. Using the NO3- : NH4+ ratio observed in the snowpack to estimate the proportion of atmospheric nitrate present in the coarse mode, we estimate that the amount of secondary NH4NO3 could double in the absence of the coarse-mode sink. The underestimation of total nitrate indicates an incomplete account of the total oxidant production during PCAP events. The ability of coarse particles to permanently remove HNO3 and influence PM2.5 formation is discussed using information about particle composition and size distribution.

Observational constraints on particle acidity using measurements and modelling of particles and gases

2017 ◽  
Vol 200 ◽  
pp. 379-395 ◽  
Author(s):  
J. G. Murphy ◽  
P. K. Gregoire ◽  
A. G. Tevlin ◽  
G. R. Wentworth ◽  
R. A. Ellis ◽  
...  
Keyword(s):  
Gas Phase ◽  
The United States ◽  
Molar Ratio ◽  
Particle Phase ◽  
Minimal Impact ◽  
Ph Values ◽  
The World ◽  
Acid Catalyzed ◽  
Field Campaigns ◽  
Condensed Phase Reactions

In many parts of the world, the implementation of air quality regulations has led to significant decreases in SO2 emissions with minimal impact on NH3 emissions. In Canada and the United States, the molar ratio of NH3 : SO2 emissions has increased dramatically between 1990 and 2014. In many regions of North America, this will lead the molar ratio of NHx : SO4, where NHx is the sum of particle phase NH4+ and gas phase NH3, and SO4 is the sum of particle phase HSO4− and SO42−, to exceed 2. A thermodynamic model (E-AIM model II) is used to investigate the sensitivity of particle pH, and the gas-particle partitioning of NHx and inorganic nitrate, to the atmospheric NHx : SO4 ratio. Steep increases in pH and the gas fraction of NHx are found as NHx : SO4 varies from below 1 to above 2. The sensitivity of the gas fraction of nitrate also depends strongly on temperature. The results show that if NHx : SO4 exceeds 2, and the gas and particle phase NHx are in equilibrium, the particle pH will be above 2. Observations of the composition of particulate matter and gas phase NH3 from two field campaigns in southern Canada in 2007 and 2012 have median NHx : SO4 ratios of 3.8 and 25, respectively. These campaigns exhibited similar amounts of NH3, but very different particle phase loadings. Under these conditions, the pH values calculated using the observations as input to the E-AIM model were in the range of 1–4. The pH values were typically higher at night because the higher relative humidity increased the particle water content, diluting the acidity. The assumption of equilibration between the gas and particle phase NHx was evaluated by comparing the observed and modelled gas fraction of NHx. In general, E-AIM was able to reproduce the partitioning well, suggesting that the dominant constituents contributing to particle acidity were measured, and that the estimated pH values were realistic. These results suggest that regions of the world where the ratio of NH3 : SO2 emissions is beginning to exceed 2 on a molar basis may be experiencing rapid increases in aerosol pH of 1–3 pH units. This could have important consequences for the rates of condensed phase reactions that are acid-catalyzed.

scholarly journals High-Frequency Gaseous and Particulate Chemical Characterization using Extractive Electrospray Ionization Mass Spectrometry (Dual-Phase-EESI-TOF)

2021 ◽  
Author(s):  
Chuan Ping Lee ◽  
Mihnea Surdu ◽  
David M. Bell ◽  
Josef Dommen ◽  
Mao Xiao ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Electrospray Ionization ◽  
Real Time ◽  
Gas Phase ◽  
Ionization Mass Spectrometry ◽  
Formation Mechanisms ◽  
Ionization Mass ◽  
Ambient Atmosphere ◽  
Dual Phase ◽  
Particle Phase

Abstract. To elucidate the sources and chemical reaction pathways of organic vapors and particulate matter in the ambient atmosphere, real-time detection of both gas and particle phase is needed. State-of-the-art techniques often suffer from thermal decomposition, ionization-induced fragmentation, high cut-off size of aerosols or low time resolution. In response to all these limitations, we developed a new technique that uses extractive electrospray ionization (EESI) for online gas and particle chemical speciation, namely the dual-phase extractive electrospray ionization time-of-flight mass spectrometer (Dual-Phase-EESI-TOF or Dual-EESI in short). The Dual-EESI was designed and optimized to measure gas- and particle-phase species with saturation vapor concentrations spanning more than 10 orders of magnitude with good linearity and a measurement cycle as fast as 3 min. The gas-phase selectivity of the Dual-EESI was compared with that of nitrate chemical ionization mass spectrometry. In addition, we performed organic aerosol uptake experiments to characterize the relative gas and particle response factors. In general, the Dual-EESI is more sensitive toward gas-phase analytes as compared to their particle-phase counterparts. The real-time measurement capability of the Dual-EESI for chemically speciated gas- and particle-phase measurements can provide new insights into aerosol sources or formation mechanisms, where gas-particle partitioning behavior can be determined after absolute parameterization of the gas/particle sensitivity.

scholarly journals Evaluating the sensitivity of fine particulate matter (PM<sub>2.5</sub>) simulations to chemical mechanism in Delhi

2020 ◽  
Author(s):  
Chinmay Jena ◽  
Sachin D. Ghude ◽  
Rachana Kulkarni ◽  
Sreyashi Debnath ◽  
Rajesh Kumar ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Air Quality ◽  
Gas Phase ◽  
Optical Depth ◽  
Fine Particulate Matter ◽  
Chemical Mechanism ◽  
Aerosol Composition ◽  
Gangetic Plain ◽  
Fine Particulate ◽  
Phase Chemical

Abstract. Elevated levels of fine particulate matter (PM2.5) during winter-time have become one of the most important environmental concerns over the Indo-Gangetic Plain (IGP) region of India, and particularly for Delhi. Accurate reconstruction of PM2.5, its optical properties, and dominant chemical components over this region is essential to evaluate the performance of the air quality models. In this study, we investigated the effect of three different aerosol mechanisms coupled with gas-phase chemical schemes on simulated PM2.5 mass concentration in Delhi using the Weather Research and Forecasting model with the Chemistry module (WRF-Chem). The model was employed to cover the entire northern region of India at 10 km horizontal spacing. Results were compared with comprehensive filed data set on dominant PM2.5 chemical compounds from the Winter Fog Experiment (WiFEX) at Delhi, and surface PM2.5 observations in Delhi (17 sites), Punjab (3 sites), Haryana (4 sites), Uttar Pradesh (7 sites) and Rajasthan (17 sites). The Model for Ozone and Related Chemical Tracers (MOZART-4) gas-phase chemical mechanism coupled with the Goddard Chemistry Aerosol Radiation and Transport (GOCART) aerosol scheme (MOZART-GOCART) were selected in the first experiment as it is currently employed in the operational air quality forecasting system of Ministry of Earth Sciences (MoES), Government of India. Other two simulations were performed with the MOZART-4 gas-phase chemical mechanism coupled with the Model for Simulating Aerosol Interactions and Chemistry (MOZART-MOSAIC), and Carbon Bond 5 (CB-05) gas-phase mechanism couple with the Modal Aerosol Dynamics Model for Europe/Secondary Organic Aerosol Model (CB05-MADE/SORGAM) aerosol mechanisms. The evaluation demonstrated that chemical mechanisms affect the evolution of gas-phase precursors and aerosol processes, which in turn affect the optical depth and overall performance of the model for PM2.5. All the three coupled schemes, MOZART-GOCART, MOZART-MOSAIC, and CB05-MADE/SORGAM, underestimate the observed concentrations of major aerosol composition (NO3−, SO42−, Cl−, BC, OC, and NH4+) and precursor gases (HNO3, NH3, SO2, NO2, and O3) over Delhi. Comparison with observations suggests that the simulations using MOZART-4 gas-phase chemical mechanism with MOSAIC aerosol performed better in simulating aerosols over Delhi and its optical depth over the IGP. The lowest NMB (−18.8 %, MB = −27.4 μg/m3) appeared for the simulations using MOZART-MOSAIC scheme, whereas the NMB was observed 32.5 % (MB = −47.5 μg/m3) for CB05-MADE/SORGAM and −53.3 % (MB = −78 μg/m3) for MOZART-GOCART scheme.

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