Emission Source Regions Research Articles

Characterizing and sourcing ambient PM2.5 over key emission regions in China II: Organic molecular markers and CMB modeling

From November 2012 to July 2013, a sampling campaign was completed for comprehensive characterization of PM2.5 over four key emission regions in China: Beijing-Tianjin-Hebei (BTH), Yangzi River Delta (YRD), Pearl River Delta (PRD), and Sichuan Basin (SB). A multi-method approach, adopting different analytical and receptor modeling methods, was employed to determine the relative abundances of region-specific air pollution constituents and contributions of emission sources. This paper is focused on organic molecular marker based source apportionment using chemical mass balance (CMB) receptor modeling. Analyses of the organic molecular markers revealed that vehicle emission, coal combustion, biomass burning, meat cooking and natural gas combustion were the major contributors to organic carbon (OC) in PM2.5. The vehicle emission dominated the sources contributing to OC in spring at four sampling sites. During wintertime, the coal combustion had highest contribution to OC at BTH site, while the major source contributing to OC at YRD and PRD sites was vehicle emission. In addition, the relative contributions of different emission sources to PM2.5 mass at a specific location site and in a specific season revealed seasonal and spatial variations across all four sampling locations. The largest contributor to PM2.5 mass was secondary sulfate (14–17%) in winter at the four sites. The vehicle emission was found to be the major source (14–21%) for PM2.5 mass at PRD site. The secondary ammonium has minor variation (4–5%) across the sites, confirming the influences of regional emission sources on these sites. The distinct patterns of seasonal and spatial variations of source apportionment observed in this study were consistent with the findings in our previous paper based upon water-soluble ions and carbonaceous fractions. This makes it essential for the local government to make season- and region-specific mitigation strategies for abating PM2.5 pollution in China.

Decadal-scale relationship between measurements of aerosols, land-use change, and fire over Southeast Asia

Abstract. A simultaneous analysis of 13 years of remotely sensed data of land cover, fires, precipitation, and aerosols from the MODIS, TRMM, and MISR satellites and the AERONET network over Southeast Asia is performed, leading to a set of robust relationships between land-use change and fire being found on inter-annual and intra-annual scales over Southeast Asia, reflecting the heavy amounts of anthropogenic influence over land-use change and fires in this region of the world. First, we find that fires occur annually, but with a considerable amount of variance in their onset, duration, and intensity from year to year, and from two separate regions within Southeast Asia. Second, we show that a simple regression model of the land-cover, fire, and precipitation data can be used to recreate a robust representation of the timing and magnitude of measured aerosol optical depth (AOD) from multiple measurements sources of this region using either 8-day (better for onset and duration) or monthly (better for magnitude) measurements, but not daily measurements. We find that the reconstructed AOD matches the timing and intensity from AERONET measurements to within 70 to 90 % and the timing and intensity of MISR measurements to within 50 to 95 %. This is a unique finding in this part of the world since cloud-covered regions are large, yet the model is still robustly capable, including over regions where no fires are observed and hence no emissions would be expected to contribute to AOD. Third, we determine that while Southeast Asia is a source region of such intense smoke emissions, portions of it are also impacted by smoke transported from other regions. There are regions in northern Southeast Asia which have two annual AOD peaks, one during the local fire season and the other, smaller peak corresponding to a combination of some local smoke sources as well as transport of aerosols from fires in southern Southeast Asia and possibly even from anthropogenic sources in South Asia. Overall, this study highlights the importance of taking into account a simultaneous use of land-use, fire, and precipitation for understanding the impacts of fires on the atmospheric loading and distribution of aerosols in Southeast Asia over both space and time. Furthermore, it highlights that there are significant advantages of using 8-day and monthly average values (instead of daily data) in order to better quantify the magnitude and timing of Southeast Asia fires.

Size-selected black carbon mass distributions and mixing state in polluted and clean environments of northern India

Abstract. We have measured black carbon properties by using a size-selected single-particle soot photometer (SP2). The measurements were conducted in northern India at two sites: Gual Pahari is located at the Indo-Gangetic Plain (IGP) and Mukteshwar at the Himalayan foothills. Northern India is known as one of the absorbing aerosol hot spots, but detailed information about absorbing aerosol mixing state is still largely missing. Previous equivalent black carbon (eBC) mass concentration measurements are available for this region, and these are consistent with our observations showing that refractory black carbon (rBC) concentrations are about 10 times higher in Gual Pahari than those at Mukteshwar. Also, the number fraction of rBC-containing particles is higher in Gual Pahari, but individual rBC-containing particles and their size distributions are fairly similar. These findings indicate that particles at both sites have similar local and regional emission sources, but aerosols are also transported from the main source regions (IGP) to the less polluted regions (Himalayan foothills). Detailed examination of the rBC-containing particle properties revealed that they are most likely irregular particles such as fractal aggregates, but the exact structure remains unknown.

Black carbon indirect radiative effects in a climate model

The aerosol–cloud interactions due to black carbon (BC) aerosols, as well as the implied climate responses, are examined using an aerosol module in the coupled atmosphere–ocean general circulation model MPI-ESM. BC is simulated to enhance cloud droplet number concentration (CDNC) by 10–15% in the BC emission source regions, especially in the Tropics and mid-latitudes. Higher CDNC and reduced auto-conversion from cloud water to rain water explains the increased cloud water path over the tropical regions (30S–30N) in the model. In the global mean, the cloud water– as well as precipitation changes are negligibly small. The global-mean effective radiative forcing due to aerosol–cloud interactions for BC is estimated at , which is attributable to the increase in CDNC burden and (regionally) cloud water in the model. Global mean temperature and rainfall response were found to be and , respectively, with significantly larger regional changes mainly in the downwind regions from BC sources.

A three-year investigation of daily PM2.5 main chemical components in four sites: the routine measurement program of the Supersito Project (Po Valley, Italy)

The Supersito Project (www.supersito-er.it) has been active in the Emilia-Romagna region, southern part of the Po Valley (Italy), since 2011. Focal aim of the project is to enhance the knowledge on atmospheric aerosol and its impact on human health. In the framework of Supersito, major chemical components of daily PM2.5 were investigated over a period of more than three years at four sampling sites, representative of dissimilar territorial conditions: one rural background (SPC) and three urban background sites in the coastal (RN), central (MS) and inner area (PR) of the region.In all the sites, organic and elemental carbon and water soluble inorganic ions accounted for more than 70% of PM2.5 mass, during all seasons. Nitrate and organic carbon (OC) were the main components of winter PM2.5, while summer aerosol was mainly contributed by OC and sulphate. OC was dominated by primary sources, with a potentially important contribution from biomass burning, in winter, while secondary processes dominated OC production in summer.A substantial homogeneity was observed on a regional scale in terms of spatial distribution of pollutants, with EC only presenting significant differences between urban and rural areas during winters. Nonetheless, differences were observed between the coastal and the inner part of the region, with the former being systematically characterized by higher concentrations of carbonaceous compounds and lower concentrations of ammonium nitrate. The coastal area was likely influenced by the aged OC from the Po Valley outflow in addition to local sources, while the scarcity of local sources of ammonia limited the formation of ammonium nitrate.In the studied area, local and regional meteorology - mostly governed by geographical collocation and orography – was responsible for PM2.5 mass and composition no less than local and regional emission sources.

Impact of harbour emissions on ambient PM10 and PM2.5 in Barcelona (Spain): Evidences of secondary aerosol formation within the urban area

With the objective of estimating the impact of harbour activities on ambient PM10 and PM2.5 levels at the urban area of Barcelona, a one year long monitoring campaign was carried out in the context of the European APICE project (MED-FEDER-EC). This campaign was simultaneously conducted at the port and a central urban background site. A detailed PM10 and PM2.5 chemical speciation analysis was carried out with samples from both sites. Subsequently, a source apportionment analysis by means of the PMF receptor model was performed. Six common factors were identified, explaining local to regional emission sources (fuel oil combustion, industrial emissions, mineral-road dust resuspension, and road traffic emissions) and aerosol formation/transformation processes (secondary aerosols including ammonium sulphate and organic aerosols, and a mixed source accounting for aged sea spray and secondary nitrate).Around 50–55% PM10 and PM2.5 measured at the port was attributed to harbour activities: mineral matter from road dust and construction works of a new port area, vehicle traffic and fuel oil combustion. The estimated contribution of harbour emissions to the urban background reached 9–12% for PM10 and 11–15% for PM2.5 and is linked to primary emissions from fuel oil combustion but also to the formation of secondary aerosols. It becomes relevant to highlight the significantly higher contribution of secondary aerosols at the urban background when compared with the harbour site. Our hypothesis points to the fast formation of secondary ammonium sulphate within the city, after the reaction of SO2/H2SO4 transported by sea breezes with NH3, which is emitted in large amounts in Barcelona; and also to the enhanced formation of secondary organic aerosols within the city. This study broadens our knowledge on atmospheric phenomenology in urban Mediterranean cities and claims for effective abatement strategies focused on maritime practises, in agreement with the driving axis of the APICE project.

Prospective air pollutant emissions inventory for the development and production of unconventional natural gas in the Karoo basin, South Africa

The increased use of horizontal drilling and hydraulic fracturing techniques to produce gas from unconventional deposits has led to concerns about the impacts to local and regional air quality. South Africa has the 8th largest technically recoverable shale gas reserve in the world and is in the early stages of exploration of this resource. This paper presents a prospective air pollutant emissions inventory for the development and production of unconventional natural gas in South Africa's Karoo basin. A bottom-up Monte Carlo assessment of nitrogen oxides (NOx = NO + NO2), particulate matter less than 2.5 μm in diameter (PM2.5), and non-methane volatile organic compound (NMVOC) emissions was conducted for major categories of well development and production activities. NOx emissions are estimated to be 68 tons per day (±42; standard deviation), total NMVOC emissions are 39 tons per day (±28), and PM2.5 emissions are 3.0 tons per day (±1.9). NOx and NMVOC emissions from shale gas development and production would dominate all other regional emission sources, and could be significant contributors to regional ozone and local air quality, especially considering the current lack of industrial activity in the region. Emissions of PM2.5 will contribute to local air quality, and are of a similar magnitude as typical vehicle and industrial emissions from a large South African city. This emissions inventory provides the information necessary for regulatory authorities to evaluate emissions reduction opportunities using existing technologies and to implement appropriate monitoring of shale gas-related activities.

CONTINUUM ENHANCEMENTS IN THE ULTRAVIOLET, THE VISIBLE AND THE INFRARED DURING THE X1 FLARE ON 2014 MARCH 29

ABSTRACT Enhanced continuum brightness is observed in many flares (“white light flares”), yet it is still unclear which processes contribute to the emission. To understand the transport of energy needed to account for this emission, we must first identify both the emission processes and the emission source regions. Possibilities include heating in the chromosphere causing optically thin or thick emission from free-bound transitions of Hydrogen, and heating of the photosphere causing enhanced H− continuum brightness. To investigate these possibilities, we combine observations from Interface Region Imaging Spectrograph (IRIS), SDO/Helioseismic and Magnetic Imager, and the ground-based Facility Infrared Spectrometer instrument, covering wavelengths in the far-UV, near-UV (NUV), visible, and infrared during the X1 flare SOL20140329T17:48. Fits of blackbody spectra to infrared and visible wavelengths are reasonable, yielding radiation temperatures ∼6000–6300 K. The NUV emission, formed in the upper photosphere under undisturbed conditions, exceeds these simple fits during the flare, requiring extra emission from the Balmer continuum in the chromosphere. Thus, the continuum originates from enhanced radiation from photosphere (visible-IR) and chromosphere (NUV). From the standard thick-target flare model, we calculate the energy of the nonthermal electrons observed by Reuven Ramaty High Energy Solar Spectroscope Imager (RHESSI) and compare it to the energy radiated by the continuum emission. We find that the energy contained in most electrons >40 keV, or alternatively, of ∼10%–20% of electrons >20 keV is sufficient to explain the extra continuum emission of ∼(4–8) × 1010 erg s−1 cm−2. Also, from the timing of the RHESSI HXR and the IRIS observations, we conclude that the NUV continuum is emitted nearly instantaneously when HXR emission is observed with a time difference of no more than 15 s.

Local and Regional Contributions to Fine Particle Pollution in Winter of the Yangtze River Delta, China

ABSTRACTThe Yangtze River Delta (YRD) is one of the most developed and heavily polluted regions in China. Understanding the origin of fine particles is necessary for policy making on air pollution control in this region. However, the current studies on quantifying the contributions from different emission source regions are limited, especially for winter pollution. In this study, field observations and scenario analysis simulations were performed by using the Weather Research and Forecasting and Community Multi-scale Air Quality (WRF/CMAQ) model to quantify the impacts of local emissions and long-range regional transport in a winter period of 2011. The results indicated that the local contributions were dominant on average in the whole period, especially for slight or medium pollution hours. However, when particle pollution increased, the effects of long-range regional transport significantly increased. The inner-regional effects from Jiangsu and the outer-regional effects from the upwind adjacent province, Shandong, are crucial for the YRD region. The dominant contributor could be local accumulation or long-range regional transport, which usually depends on the weather conditions. This study provides a systematic analysis of the characteristics and origins of winter pollution in the YRD according to combined observations and modeling, which is helpful for understanding regional particle pollution formation and policy making on improving air quality in this region.

Distribution, input pathway and mass inventory of black carbon in sediments of the Gulf of Thailand, SE Asia

The coastal margins around Southeast Asia (SE Asia) may serve as an ideal location to study the source-sink process of sedimentary black carbon (BC) because SE Asia has been identified as one of the major BC emission source regions in the world. This study provides an extensive picture of recent regional-scale sedimentary BC sequestration in the Gulf of Thailand (GOT), a tropical marine system in SE Asia. Generally, the sedimentary BC concentrations (0.07–3.99 mg/g) were in the low to moderate ranges of those obtained in other coastal sediments around the world. Regional variability of the BC and its correlation with the sediment grain size and total organic carbon (TOC) content indicated a general hydrodynamic constraint on BC occurrence in the lower Gulf in contrast to the upper Gulf with a more source dependence due to the direct land-based input. BC/TOC% values and the varied BC components (char and soot), as well as their correlations suggested that char was the predominant constituents of sedimentary BC both in the upper and lower Gulf, which could be mainly derived from biomass burning and entered into the nearshore region through direct fluvial transport and surface run-off. The estimated BC burial flux (∼212 μg/cm2/y) and mass inventory (∼200 Gg/y) in the GOT on the hundred-year timescale were of the same order of magnitude compared with other oceanic margins, and thus the tropical shelf sediments from SE Asia could serve as an important sink of land-emitted BC.

Absorbing and scattering aerosols over the source region of biomass burning emissions: Implications in the assessment of optical and radiative properties

Abstract The current study focuses on the assessment of model simulated optical and radiative properties of aerosols incorporating the measured chemical composition of aerosol samples collected at Patiala during October, 2011–February, 2012. Monthly average mass concentration of PM2.5, elemental carbon (EC), primary organic carbon (POC), water-soluble (WS) and insoluble (INS) aerosols ranged from 120 to 192, 6.2 to 7.2, 20 to 39, 59 to 111 and 35 to 90 μg m−3, respectively. Mass concentration of different components of aerosols was further used for the assessment of optical properties derived from Optical Properties of Aerosols and Clouds (OPAC) model simulations. Microtops based measured aerosol optical depth (AOD500) ranged from 0.47 to 0.62 showing maximum value during November and December, and minimum during February. Angstrom exponent (α380-870) remained high (>0.90) throughout the study period except in February (0.74), suggesting predominance of fine mode particles over the study region. The observed ratio of scattering to absorbing aerosols was incorporated in OPAC model simulations and single scattering albedo (SSA at 500 nm) so obtained ranged between 0.80 and 0.92 with relatively low values during the period of extensive biomass burning. In the present study, SBDART based estimated values of aerosol radiative forcing (ARF) at the surface (SRF) and top of the atmosphere (TOA) ranged from −31 to −66 Wm-2 and -2 to −18 W m−2 respectively. The atmospheric ARF, ranged between + 18 and + 58 Wm-2 resulting in the atmospheric heating rate between 0.5 and 1.6 K day−1. These results signify the role of scattering and absorbing aerosols in affecting the magnitude of aerosol forcing.

Analysis of the 2014 “APEC Blue” in Beijing Using More than One Decade of Satellite Observations: Lessons Learned from Radical Emission Control Measures

During the 2014 Asia-Pacific Economic Cooperation (APEC) Economic Leaders’ Meetings in Beijing, the Chinese government made significant efforts to clear Beijing’s sky. The emission control measures were very effective and the improved air quality during the APEC Meetings was called the “APEC Blue”. To monitor and estimate how these emission control measures affected air quality in Beijing and its five neighboring large cities (Tianjin, Shijiazhuang, Tangshan, Jinan, and Qingdao), we compared and analyzed the satellite-retrieved Aerosol Optical Thickness (AOT) products of the pre-APEC (18–31 October), APEC (1–11 November), and post-APEC periods (11–31 November) in 2002–2014 and daily PM2.5 measurements of the three periods in 2014 on the ground. Compared with the pre- and post-APEC periods, both ground and satellite observations indicated significantly reduced aerosol loading during the 2014 APEC period in Beijing and its surroundings, but with apparent spatial heterogeneity. For example, the peak value of PM2.5 in Beijing were around 100 µg∙m−3 during the APEC period, however, during the pre- and post-APEC periods, the peak values were up to 290 µg∙m−3. The following temporal correlation analysis of mean AOT values between Beijing and other five cities for the past thirteen years (2002–2014) indicated that the potential emission source regions strongly impacting air quality of Beijing were confined within central and southern Hebei as well as northern and southwestern Shandong, in correspondence with the spatial pattern of Digital Earth Model (DEM) of the study region. In addition to stringent emission control measures, back trajectory analysis indicated that the relatively favorable regional transport pattern might also have contributed to the “APEC Blue” in Beijing. These results suggest that the “APEC Blue” is a temporarily regional phenomenon; a long-term improvement of air quality in Beijing is still challenging and joint efforts of the whole region are needed.

Variations in carbonaceous species at a high-altitude site in western India: Role of synoptic scale transport

Atmospheric fine-mode particulate matter (PM2.5), collected during January to December 2007 at a high-altitude site (Mt. Abu, 24.6°N, 72.7°E, 1680 m asl) in the western India, have been analysed for carbonaceous and inorganic species to assess their temporal variability and the influence of emissions and transport processes, particularly from the Indo-Gangetic Plain (IGP). The mass concentrations (μg m−3) of elemental carbon (EC), organic carbon (OC) and water-soluble OC (WSOC) are observed to be the highest during winter months, and found to vary between 0.2 and 2.8, 0.5–9.8 and 0.4–8.7, respectively. This variation in mass concentration is attributed to the synoptic scale long-range transport from the emission source regions in the Indo-Gangetic Plain (IGP). Relatively lower fractional contribution of carbonaceous species to PM2.5 mass is found during March–September. This is mainly attributed to the reduction in strength of biomass burning emissions near the study site, increase in boundary layer height and simultaneous increase in mineral dust concentration via transport from the Thar Desert and Arabian Peninsula. However, the OC/EC ratio is nearly uniform throughout the year (5.5 ± 1.6, n = 71) and indicate towards the dominance of biomass burning emissions at Mt Abu. This is further supported by a significant correlation between nss-K+ and OC (R2 = 0.71) with nss-K+/OC ratio averaged at 0.10 ± 0.04. The higher WSOC/OC ratio (av: 0.65 ± 0.16; 1σ) compared to those in IGP, suggested formation of secondary organic aerosols during the transport, which is further attested by the observed strong correlation between secondary OC (SOC) and WSOC concentrations. A back-trajectory-assisted analysis has been performed to estimate the levels of OC, EC, WSOC, OC/EC and WSOC/OC in two distinct air-masses classified as the marine air mass and the IGP influenced air mass. This analysis shows significantly higher concentration of OC, EC and WSOC in the IGP influenced air masses by 64.9%, 121.4% and 113.2% respectively, as compared to the marine air masses. This important observation of carbonaceous aerosols at Mt Abu highlights the role of synoptic scale transport particularly from the biomass burning sources in the IGP.

Mass absorption efficiency of light absorbing organic aerosols from source region of paddy-residue burning emissions in the Indo-Gangetic Plain

Abstract The mass absorption efficiency (MAE) of light absorbing water-soluble organics, representing a significant fraction of brown carbon (BrC), has been studied in fine mode aerosols (PM2.5) from a source region (Patiala: 30.2 °N, 76.3 °E) of biomass burning emissions (BBEs) in the Indo-Gangetic Plain (IGP). The mass absorption coefficient of BrC at 365 nm (babs-365), assessed from absorption spectra of aqueous extracts, exhibits significant linear relationship with water-soluble organic carbon (WSOC) for day (R2 = 0.37) and night time (R2 = 0.77) samples; and slope of regression lines provides a measure of MAE of BrC (daytime: ∼0.75 m2 g−1 and night time: 1.13 m2 g−1). A close similarity in the temporal variability of babs-365 (for BrC) and K+ in all samples suggests their common source from BBEs. The babs-365 of BrC follows a power law (babs-λ ≈ λ−α; where α = angstrom exponent) and averages around 5.2 ± 2.0 M m−1 (where M = 10−6). A significant decrease in the MAE of BrC from the source region (this study) to the downwind oceanic region (over Bay of Bengal, Srinivas and Sarin, 2013 ) could be attributed to relative increase in the contribution of non-absorbing WSOC and/or photo-bleaching of BrC during long-range atmospheric transport. The atmospheric radiative forcing due to BrC over the study site accounts for ∼40% of that from elemental carbon (EC).

A model validation study of the washout/rainout contribution of sulfate and nitrate in wet deposition compared with precipitation chemistry data in Japan

We simulated washout/rainout ratios of non-sea-salt (nss)-SO42− and NO3− using a chemical transport model and compared the estimates with precipitation measurements sampled at 0.5/1 mm intervals at sites located in Kobe (urban), Toyo-oka (suburban), and Tamba (rural) cities, Japan. The 25th and 75th percentile range of the simulated washout contributions was 30–70%. The simulated washout contribution range of NO3− (40–70%) was greater than that of nss-SO42− (30–60%). There was good agreement between the simulated and observed values, and the observed washout contribution of NO3− was also greater than that of SO42−. The simulated washout contribution range was higher (60–75%) in emission source regions and lower (40–55%) in downwind areas. The wet deposition process is one of the key causes of uncertainty in chemical transport modeling. Comparing model results with such high-frequency precipitation chemistry data has been extremely rare. Thus the current study is providing useful information for evaluating and improving wet deposition modeling and for the better understanding of the wet deposition mechanism.

Flux and budget of BC in the continental shelf seas adjacent to Chinese high BC emission source regions

AbstractThis study conducted the first comprehensive investigation of sedimentary black carbon (BC) concentration, flux, and budget in the continental shelves of “Bohai Sea (BS) and Yellow Sea (YS),” based on measurements of BC in 191 surface sediments, 36 riverine water, and 2 seawater samples, as well as the reported data set of the atmospheric samples from seven coastal cities in the Bohai Rim. BC concentrations in these matrices were measured using the method of thermal/optical reflectance. The spatial distribution of the BC concentration in surface sediments was largely influenced by the regional hydrodynamic conditions, with high values mainly occurring in the central mud areas where fine‐grained particles (median diameters > 6 Φ (i.e., <0.0156 mm)) were deposited. The BC burial flux in the BS and YS ranged from 4 to 1100 µg/cm2 yr, and averaged 166 ± 200 µg/cm2 yr, which was within the range of burial fluxes reported in other continental shelf regimes. The area‐integrated sedimentary BC sink flux in the entire BS and YS was ~325 Gg/yr, and the BS alone contributed ~50% (~157 Gg/yr). The BC budget calculated in the BS showed that atmospheric deposition, riverine discharge, and import from the Northern Yellow Sea (NYS) each contributed ~51%, ~47%, and ~2%. Therefore, atmospheric deposition and riverine discharge dominated the total BC influx (~98%). Sequestration to bottom sediments was the major BC output pattern, accounting for ~88% of the input BC. Water exchange between the BS and the NYS was also an important BC transport route, with net BC transport from the BS to the NYS.

Modeling dry and wet deposition of sulfate, nitrate, and ammonium ions in Jiuzhaigou National Nature Reserve, China using a source-oriented CMAQ model: Part I. Base case model results

A source-oriented Community Multiscale Air Quality (CMAQ) model driven by the meteorological fields generated by the Weather Research and Forecasting (WRF) model was used to study the dry and wet deposition of nitrate (NO3−), sulfate (SO42−), and ammonium (NH4+) ions in the Jiuzhaigou National Nature Reserve (JNNR), China from June to August 2010 and to identify the contributions of different emission sectors and source regions that were responsible for the deposition fluxes. The model performance is evaluated in this paper and the source contribution analyses are presented in a companion paper. The results show that WRF is capable of reproducing the observed precipitation rates with a Mean Normalized Gross Error (MNGE) of 8.1%. Predicted wet deposition fluxes of SO42− and NO3− at the Long Lake (LL) site (3100m a.s.l.) during the three-month episode are 2.75 and 0.34kgS(N) ha−1, which agree well with the observed wet deposition fluxes of 2.42 and 0.39kgS(N)ha−1, respectively. Temporal variations in the weekly deposition fluxes at LL are also well predicted. Wet deposition flux of NH4+ at LL is over-predicted by approximately a factor of 3 (1.60kgNha−1vs. 0.56kgNha−1), likely due to missing alkaline earth cations such as Ca2+ in the current CMAQ simulations. Predicted wet deposition fluxes are also in general agreement with observations at four Acid Deposition Monitoring Network in East Asia (EANET) sites in western China. Predicted dry deposition fluxes of SO42− (including gas deposition of SO2) and NO3− (including gas deposition of HNO3) are 0.12 and 0.12kgS(N)ha−1 at LL and 0.07 and 0.08kgS(N)ha−1 at Jiuzhaigou Bureau (JB) in JNNR, respectively, which are much lower than the corresponding wet deposition fluxes. Dry deposition flux of NH4+ (including gas deposition of NH3) is 0.21kgNha−1 at LL, and is also much lower than the predicted wet deposition flux. For both dry and wet deposition fluxes, predictions from the 12-km resolution nested domain are similar to those from the 36-km resolution parent domain.

Modeling dry and wet deposition of sulfate, nitrate, and ammonium ions in Jiuzhaigou National Nature Reserve, China using a source-oriented CMAQ model: Part II. Emission sector and source region contributions

A source-oriented Community Multiscale Air Quality (CMAQ) model driven by the meteorological fields generated by the Weather Research and Forecasting (WRF) model was used to study the dry and wet deposition of nitrate (NO3−), sulfate (SO42−), and ammonium (NH4+) ions in the Jiuzhaigou National Nature Reserve (JNNR), China from June to August 2010 and to identify the contributions of different emission sectors and source regions that were responsible for the deposition fluxes. Contributions from power plants, industry, transportation, domestic, biogenic, windblown dust, open burning, fertilizer, and manure management sources to deposition fluxes in JNNR watershed and four EANET sites are determined. In JNNR, 96%, 82%, and 87% of the SO42−, NO3− and NH4+ deposition fluxes are in the form of wet deposition of the corresponding aerosol species. Industry and power plants are the two major sources of SO42− deposition flux, accounting for 86% of the total wet deposition of SO42−, and industry has a higher contribution (56%) than that of power plants (30%). Power plants and industry are also the top sources that are responsible for NO3− wet deposition, and contributions from power plants (30%) are generally higher than those from industries (21%). The major sources of NH4+ wet deposition flux in JNNR are fertilizer (48%) and manure management (39%). Source-region apportionment confirms that SO2 and NOx emissions from local and two nearest counties do not have a significant impact on predicted wet deposition fluxes in JNNR, with contributions less than 10%. While local NH3 emissions account for a higher fraction of the NH4+ deposition, approximately 70% of NH4+ wet deposition in JNNR originated from other source regions. This study demonstrates that S and N deposition in JNNR is mostly from long-range transport rather than from local emissions, and to protect JNNR, regional emission reduction controls are needed.

Concentration and chemical composition of PM2.5 for a one-year period at Thessaloniki, Greece: A comparison between city and port area

The chemical characterization of PM2.5 fraction was studied during a one-year sampling campaign conducted at an urban area (city center) of Thessaloniki, Greece. PM2.5 samples were analyzed for polycyclic aromatic hydrocarbons, minerals and trace elements, water soluble ions, organic and elemental carbon. The average PM2.5 concentration (37.7 μg/m3) was significantly higher than the EU legislated annual limit of 25 μg/m3 underlining the temporal problems of air quality in the city. PM mass and chemical composition data collected at the city center were compared to the corresponding data which were simultaneously collected at a site near the port. The atmosphere in the port area has been found to be more aggravated compared to the city center area. Statistical analysis and diagnostic ratios of the collected chemical data at both sites were used to identify the main sources contributing to the pollutant levels: traffic, biomass burning for domestic heating, shipping and port activities and dust resuspension. In general, chemical analysis highlighted that PM2.5 mass was mainly composed by secondary inorganic aerosols and particulate organic matter, reflecting the simultaneous contribution of both regional and local emission sources.

The “APEC Blue” phenomenon: Regional emission control effects observed from space

Observations from space were used to evaluate the effect of emission control measures on the changes of air pollutants in Beijing and its surroundings during the 2014 Asia-Pacific Economic Cooperation (APEC) Summit held in Beijing. Compared to the past three years (2011–2013), NO2 tropospheric vertical column densities in 2014 were found to exhibit almost across-the-board significant reductions over the North China Plain, suggesting the effectiveness of the national policy on NOx emission reduction during China's 12th “Five-Year-Plan”. During the APEC period (Nov. 3–11), AOD and AAOD were found reduced the most in Beijing, followed by Hebei province. Stringent emission control measures implemented in Beijing and the regional joint control over the surroundings especially in Hebei were responsible for the good air quality and so-called “APEC Blue”. However, air quality plummeted during the post-APEC period (Nov. 12–30), which was largely related to the lifting of local and regional joint emission control measures. By applying a spatial correlation analysis method, the potential emission source regions impacting air quality of Beijing included widespread areas in Hebei, Shandong, Shanxi, and Tianjin in the past three years (2011–2013). While during the study period in 2014, areas impacting Beijing evidently shrank and were limited within Hebei, suggesting evident effects of intense emission perturbations on lowering the extent of regional transport. This study indicates short-term measures did fix the air pollution problems in China but a permanent solution is still a tremendous challenge.