Abstract The oxidative potential (OP) of particulate matter (PM) is a major driver of PM-associated health effects. In India, the emission sources defining PM-OP, and their local/regional nature, are ...yet to be established. Here, to address this gap we determine the geographical origin, sources of PM, and its OP at five Indo-Gangetic Plain sites inside and outside Delhi. Our findings reveal that although uniformly high PM concentrations are recorded across the entire region, local emission sources and formation processes dominate PM pollution. Specifically, ammonium chloride, and organic aerosols (OA) from traffic exhaust, residential heating, and oxidation of unsaturated vapors from fossil fuels are the dominant PM sources inside Delhi. Ammonium sulfate and nitrate, and secondary OA from biomass burning vapors, are produced outside Delhi. Nevertheless, PM-OP is overwhelmingly driven by OA from incomplete combustion of biomass and fossil fuels, including traffic. These findings suggest that addressing local inefficient combustion processes can effectively mitigate PM health exposure in northern India.
Carbonaceous aerosol is a dominant component of fine particles in Beijing. However, it is challenging to apportion its sources. Here, we applied a
newly developed method which combined radiocarbon ...(14C) with organic tracers to apportion the sources of fine carbonaceous particles at an
urban (IAP) and a rural (PG) site of Beijing. PM2.5 filter samples (24 h) were collected at both sites from 10 November to
11 December 2016 and from 22 May to 24 June 2017. 14C was determined in 25 aerosol samples (13 at IAP and 12 at PG) representing low
pollution to haze conditions. Biomass burning tracers (levoglucosan, mannosan, and galactosan) in the samples were also determined using
gas chromatography–mass spectrometry (GC-MS). Higher contributions of fossil-derived OC (OCf) were found at the urban site. The OCf / OC ratio decreased in the summer
samples (IAP: 67.8 ± 4.0 % in winter and 54.2 ± 11.7 % in summer; PG: 59.3 ± 5.7 % in winter and
50.0 ± 9.0 % in summer) due to less consumption of coal in the warm season. A novel extended Gelencsér (EG) method incorporating the
14C and organic tracer data was developed to estimate the fossil and non-fossil sources of primary and secondary OC (POC and SOC). It
showed that fossil-derived POC was the largest contributor to OC (35.8 ± 10.5 % and 34.1 ± 8.7 % in wintertime for IAP and PG,
28.9 ± 7.4 % and 29.1 ± 9.4 % in summer), regardless of season. SOC contributed 50.0 ± 12.3 % and
47.2 ± 15.5 % at IAP and 42.0 ± 11.7 % and 43.0 ± 13.4 % at PG in the winter and summer sampling periods,
respectively, within which the fossil-derived SOC was predominant and contributed more in winter. The non-fossil fractions of SOC increased in
summer due to a larger biogenic component. Concentrations of biomass burning OC (OCbb) are resolved by the extended Gelencsér method,
with average contributions (to total OC) of 10.6 ± 1.7 % and 10.4 ± 1.5 % in winter at IAP and PG and 6.5 ± 5.2 % and
17.9 ± 3.5 % in summer, respectively. Correlations of water-insoluble OC (WINSOC) and water-soluble OC (WSOC) with POC and SOC showed that
although WINSOC was the major contributor to POC, a non-negligible fraction of WINSOC was found in SOC for both fossil and non-fossil sources,
especially during winter. In summer, a greater proportion of WSOC from non-fossil sources was found in SOC. Comparisons of the source apportionment
results with those obtained from a chemical mass balance model were generally good, except for the cooking aerosol.
Comprehensive identification of aerosol sources and their constituent organic compounds requires aerosol-phase molecular-level characterization with a high time resolution. While real-time chemical ...characterization of aerosols is becoming increasingly common, information about functionalization and structure is typically obtained from offline methods. This study presents a method for determining the presence of carboxylic acid functional groups in real time using extractive electrospray ionization mass spectrometry based on measurements of M – H + 2Na+ adducts. The method is validated and characterized using standard compounds. A proof-of-concept application to α-pinene secondary organic aerosol (SOA) shows the ability to identify carboxylic acids even in complex mixtures. The real-time capability of the method allows for the observation of the production of carboxylic acids, likely formed in the particle phase on short time scales (<120 min). Our research explains previous findings of carboxylic acids being a significant component of SOA and a quick decrease in peroxide functionalization following SOA formation. We show that the formation of these acids is commensurate with the increase of dimers in the particle phase. Our results imply that SOA is in constant evolution through condensed-phase processes, which lower the volatility of the aerosol components and increase the available condensed mass for SOA growth and, therefore, aerosol mass loading in the atmosphere. Further work could aim to quantify the effect of particle-phase acid formation on the aerosol volatility distributions.
Aerodyne aerosol mass spectrometer (AMS) and Aerodyne aerosol chemical speciation monitor (ACSM) mass spectra are widely used to quantify organic aerosol (OA) elemental composition, oxidation state, ...and major environmental sources. The OA CO2 + fragment is among the most important measurements for such analyses. Here, we show that a non-OA CO2 + signal can arise from reactions on the particle vaporizer, ion chamber, or both, induced by thermal decomposition products of inorganic salts. In our tests (eight instruments, n = 29), ammonium nitrate (NH4NO3) causes a median CO2 + interference signal of +3.4% relative to nitrate. This interference is highly variable between instruments and with measurement history (percentiles P 10–90 = +0.4 to +10.2%). Other semi-refractory nitrate salts showed 2–10 times enhanced interference compared to that of NH4NO3, while the ammonium sulfate ((NH4)2SO4) induced interference was 3–10 times lower. Propagation of the CO2 + interference to other ions during standard AMS and ACSM data analysis affects the calculated OA mass, mass spectra, molecular oxygen-to-carbon ratio (O/C), and f 44. The resulting bias may be trivial for most ambient data sets but can be significant for aerosol with higher inorganic fractions (>50%), e.g., for low ambient temperatures, or laboratory experiments. The large variation between instruments makes it imperative to regularly quantify this effect on individual AMS and ACSM systems.
Particulate matter (PM) pollution on the peripheries of Chinese megacities can be as serious as in cities themselves. Given the substantial vehicular emissions in inner-city areas, the direct ...transport of primary PM (e.g., black carbon and primary organics) and effective formation of secondary PM from precursors (e.g., NOx and volatile organic compounds) can contribute to PM pollution in buffer zones between cities. To investigate how traffic emissions in inner-city areas impact these adjacent buffer zones, a suite of real-time instruments were deployed in Panyu, downwind from central Guangzhou, from November to December 2014. Nitrate mass fraction was higher on high-PM days, with the average nitrate-to-sulfate ratio increasing from around 0.35 to 1.5 as the PM mass concentration increased from 10 to 160 µg m−3. Particulate nitrate was strongly correlated with excess ammonium ((NH4+ ∕ SO42− − 1.5) × SO42−), with higher concentrations in December than in November due to lower temperatures. The organic mass fraction was the highest across all PM1 levels throughout the campaign. While organic aerosols (OA) were dominated by secondary organic aerosols (SOA = semi-volatile oxygenated organic aerosols + low-volatility oxygenated organic aerosols) as a campaign average, freshly emitted hydrocarbon-like organic aerosols (HOA) contributed up to 40 % of OA during high-OA periods, which typically occurred at nighttime and contributed 23.8 to 28.4 % on average. This was due to daytime traffic restrictions on heavy-duty vehicles in Guangzhou, and HOA almost increased linearly with total OA concentration. SOA increased as odd oxygen (Ox = O3 + NO2) increased during the day due to photochemistry. A combination of nighttime traffic emissions and daytime photochemistry contributed to the buildup of PM in Panyu. The mitigation of PM pollution in inner-city areas by reducing vehicular traffic can potentially improve air quality in peripheral areas.
The Xact 625 Ambient Metals Monitor was tested during a 3-week field campaign at the rural, traffic-influenced site Härkingen in Switzerland during the summer of 2015. The field campaign encompassed ...the Swiss National Day fireworks event, providing increased concentrations and unique chemical signatures compared to non-fireworks (or background) periods. The objective was to evaluate the data quality by intercomparison with other independent measurements and test its applicability for aerosol source quantification. The Xact was configured to measure 24 elements in PM10 with 1 h time resolution. Data quality was evaluated for 10 24 h averages of Xact data by intercomparison with 24 h PM10 filter data analysed with ICP-OES for major elements, ICP-MS for trace elements, and gold amalgamation atomic absorption spectrometry for Hg. Ten elements (S, K, Ca, Ti, Mn, Fe, Cu, Zn, Ba, Pb) showed excellent correlation between the compared methods, with r2 values ≥ 0.95. However, the slopes of the regressions between Xact 625 and ICP data varied from 0.97 to 1.8 (average 1.28) and thus indicated generally higher Xact elemental concentrations than ICP for these elements. Possible reasons for these differences are discussed, but further investigations are needed. For the remaining elements no conclusions could be drawn about their quantification for various reasons, mainly detection limit issues. An indirect intercomparison of hourly values was performed for the fireworks peak, which brought good agreement of total masses when the Xact data were corrected with the regressions from the 24 h value intercomparison. The results demonstrate that multi-metal characterization at high-time-resolution capability of Xact is a valuable and practical tool for ambient monitoring.
To assign fossil and nonfossil contributions to carbonaceous particles, radiocarbon (14C) measurements were performed on organic carbon (OC), elemental carbon (EC), and water-insoluble OC (WINSOC) of ...aerosol samples from a regional background site in South China under different seasonal conditions. The average contributions of fossil sources to EC, OC and WINSOC were 38 ± 11%, 19 ± 10%, and 17 ± 10%, respectively, indicating generally a dominance of nonfossil emissions. A higher contribution from fossil sources to EC (∼51%) and OC (∼30%) was observed for air-masses transported from Southeast China in fall, associated with large fossil-fuel combustion and vehicle emissions in highly urbanized regions of China. In contrast, an increase of the nonfossil contribution by 5–10% was observed during the periods with enhanced open biomass-burning activities in Southeast Asia or Southeast China. A modified EC tracer method was used to estimate the secondary organic carbon from fossil emissions by determining 14C-derived fossil WINSOC and fossil EC. This approach indicates a dominating secondary component (70 ± 7%) of fossil OC. Furthermore, contributions of biogenic and biomass-burning emissions to contemporary OC were estimated to be 56 ± 16% and 44 ± 14%, respectively.
Atmospheric aerosol particles are a complex combination of primary emitted
sources (biogenic and anthropogenic) and secondary aerosol resulting from
aging processes such as condensation, coagulation, ...and cloud processing. To
better understand their sources, investigations have been focused on urban
areas in the past, whereas rural-background stations are normally less
impacted by surrounding anthropogenic sources. Therefore, they are
predisposed for studying the impact of long-range transport of anthropogenic
aerosols. Here, the chemical composition and organic aerosol (OA) sources of
submicron aerosol particles measured by an aerosol chemical speciation
monitor (ACSM) and a multi-angle absorption photometer (MAAP) were
investigated at Melpitz from September 2016 to August 2017. The location of
the station at the frontier between western and eastern Europe makes it the
ideal place to investigate the impact of long-range transport over Europe.
Indeed, the station is under the influence of less polluted air masses from
westerly directions and more polluted continental air masses from eastern
Europe. The OA dominated the submicron particle mass concentration and
showed strong seasonal variability ranging from 39 % (in winter) to 58 % (in summer). It was followed by sulfate (15 % and 20 %) and
nitrate (24 % and 11 %). The OA source identification was performed
using the rolling positive matrix factorization (PMF) approach to account
for the potential temporal changes in the source profile. It was
possible to split OA into five factors with a distinct temporal variability
and mass spectral signature. Three were associated with anthropogenic
primary OA (POA) sources: hydrocarbon-like OA (HOA; 5.2 % of OA mass in
winter and 6.8 % in summer), biomass burning OA (BBOA; 10.6 % and 6.1 %) and coal combustion OA (CCOA; 23 % and 8.7 %). Another two are
secondary and processed oxygenated OA (OOA) sources: less oxidized OOA (LO-OOA;
28.4 % and 36.7 %) and more oxidized OOA (MO-OOA; 32.8 % and 41.8 %). Since equivalent black carbon (eBC) was clearly associated with the
identified POA factors (sum of HOA, BBOA, and CCOA; R2= 0. 87), eBC's
contribution to each of the POA factors was achieved using a multilinear
regression model. Consequently, CCOA represented the main anthropogenic
sources of carbonaceous aerosol (sum of OA and eBC) not only during winter
(56 % of POA in winter) but also in summer (13 % of POA in summer),
followed by BBOA (29 % and 69 % of POA in winter and summer,
respectively) and HOA (15 % and 18 % of POA in winter and summer,
respectively). A seasonal air mass cluster analysis was used to understand
the geographical origins of the different aerosol types and showed that
during both winter and summer time, PM1 (PM with an aerodynamic
diameter smaller than 1 µm) air masses with eastern influence were
always associated with the highest mass concentration and the highest coal
combustion fraction. Since during wintertime CCOA is a combination of
domestic heating and power plant emissions, the summer contribution of CCOA
emphasizes the critical importance of coal power plant emissions to
rural-background aerosols and its impact on air quality, through long-range
transportation.
Reactive oxygen species (ROS) are believed to contribute
to the adverse health effects of aerosols. This may happen by inhaled
particle-bound (exogenic) ROS (PB-ROS) or by ROS formed within the
...respiratory tract by certain aerosol components (endogenic ROS). We
investigated the chemical composition of aerosols and their exogenic ROS
content at the two contrasting locations Beijing (China) and Bern
(Switzerland). We apportioned the ambient organic aerosol to different
sources and attributed the observed water-soluble PB-ROS to them. The
oxygenated organic aerosol (OOA, a proxy for secondary organic aerosol, SOA)
explained the highest fraction of the exogenic ROS concentration variance at
both locations. We also characterized primary and secondary aerosol
emissions generated from different biogenic and anthropogenic sources in
smog chamber experiments. The exogenic PB-ROS content in the OOA from these
emission sources was comparable to that in the ambient measurements. Our
results imply that SOA from gaseous precursors of different anthropogenic
emission sources is a crucial source of water-soluble PB-ROS and should be
additionally considered in toxicological and epidemiological studies in an
adequate way besides primary emissions. The importance of PB-ROS may be
connected to the seasonal trends in health effects of PM reported by
epidemiological studies, with elevated incidences of adverse effects in
warmer seasons, which are accompanied by more-intense atmospheric oxidation
processes.
Biogenic volatile organic compound (BVOC) emissions are one of
the essential inputs for chemical transport models (CTMs), but their
estimates are associated with large uncertainties, leading to ...significant
influence on air quality modelling. This study aims to investigate the
effects of using different BVOC emission models on the performance of a CTM
in simulating secondary pollutants, i.e. ozone, organic, and inorganic
aerosols. European air quality was simulated for the year 2011 by the
regional air quality model Comprehensive Air Quality Model with Extensions
(CAMx) version 6.3, using BVOC emissions calculated by two emission models:
the Paul Scherrer Institute (PSI) model and the Model of Emissions of Gases
and Aerosol from Nature (MEGAN) version 2.1. Comparison of isoprene and monoterpene
emissions from both models showed large differences in their general amounts,
as well as their spatial distribution in both summer and winter. MEGAN
produced more isoprene emissions by a factor of 3 while the PSI model
generated 3 times the monoterpene emissions in summer, while there was
negligible difference (∼4 %) in sesquiterpene emissions
associated with the two models. Despite the large differences in isoprene
emissions (i.e. 3-fold), the resulting impact in predicted summertime ozone
proved to be minor (<10 %; MEGAN O3 was higher than
PSI O3 by ∼7 ppb). Comparisons with measurements from the
European air quality database (AirBase) indicated that PSI emissions might
improve the model performance at low ozone concentrations but worsen performance at
high ozone levels (>60 ppb). A much larger effect of the
different BVOC emissions was found for the secondary organic aerosol (SOA)
concentrations. The higher monoterpene emissions (a factor of ∼3) by the PSI model led to higher SOA by ∼110 % on average
in summer, compared to MEGAN, and lead to better agreement between modelled and
measured organic aerosol (OA): the mean bias between modelled and measured OA
at nine measurement stations using Aerodyne aerosol chemical speciation monitors
(ACSMs) or Aerodyne aerosol mass
spectrometers (AMSs) was reduced by 21 %–83 % at rural or remote stations. Effects on inorganic aerosols (particulate
nitrate, sulfate, and ammonia) were relatively small (<15 %).
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