Regional Haze Research Articles

Evaluation of assumptions for estimating chemical light extinction at U.S. national parks

Studies were conducted at Great Smoky Mountains National Park (NP) (GRSM), Tennessee, Mount Rainier NP (MORA), Washington, and Acadia NP (ACAD), Maine, to evaluate assumptions used to estimate aerosol light extinction from chemical composition. The revised IMPROVE equation calculates light scattering from concentrations of PM2.5 sulfates, nitrates, organic carbon mass (OM), and soil. Organics are assumed to be nonhygroscopic. Organic carbon (OC) is converted to OM with a multiplier of 1.8. Experiments were conducted to evaluate assumptions on aerosol hydration state, the OM/OC ratio, OM hygroscopicity, and mass scattering efficiencies. Sulfates were neutralized by ammonium during winter at GRSM (W, winter) and at MORA during summer but were acidic at ACAD and GRSM (S, summer) during summer. Hygroscopic growth was mostly smooth and continuous, rarely exhibiting hysteresis. Deliquescence was not observed except infrequently during winter at GRSM (W). Water-soluble organic carbon (WSOC) was separated from bulk OC with solid-phase absorbents. The average OM/OC ratios were 2.0, 2.7, 2.1, and 2.2 at GRSM (S), GRSM (W), MORA, and ACAD, respectively. Hygroscopic growth factors (GF) at relative humidity (RH) 90% for aerosols generated from WSOC extracts averaged 1.19, 1.06, 1.13, and 1.16 at GRSM (S), GRSM (W), MORA, and ACAD, respectively. Thus, the assumption that OM is not hygroscopic may lead to underestimation of its contribution to light scattering.Implications: Studies at IMPROVE sites conducted in U.S. national parks showed that aerosol organics comprise more PM2.5 mass and absorb more water as a function of relative humidity than is currently assumed by the IMPROVE equation for calculating chemical light extinction. Future strategies for reducing regional haze may therefore need to focus more heavily on understanding the origins and control of anthropogenic sources of organic aerosols.

Analysis of a severe prolonged regional haze episode in the Yangtze River Delta, China

A severe prolonged regional haze episode occurred over the Yangtze River Delta (YRD) from 2 to 14 December 2013. In this paper, we have discussed the probable cause of haze episode and aerosol characteristics. Analysis of visibility and meteorological parameters suggest that the meteorological conditions play a very important role in the accumulation of aerosol particles that cause haze. The height of the planetary boundary layer (PBL) is considered as one of the key factors together with other factors in the haze formation.The Principal Component Analysis (PCA) clearly shows accumulation process of air pollutants from vehicular, industrial and anthropogenic sources are major contributors for the haze formation. The aerosol optical properties (aerosol optical depth – AOD, Ångström exponent – α and Ultra Violet Aerosol Index – UVAI) are analyzed to study the temporal and spatial variations of aerosol loadings. The results show concentrations of fine mode particles during the haze episode, the dust could have been also entered in the region from the northwestern China. Analysis of vertical aerosol profiles indicate that dust aerosols concentrated in the lower part of the haze layers.

U.S. National PM2.5 Chemical Speciation Monitoring Networks—CSN and IMPROVE: Description of networks

The U.S. Environmental Protection Agency (EPA) initiated the national PM2.5 Chemical Speciation Monitoring Network (CSN) in 2000 to support evaluation of long-term trends and to better quantify the impact of sources on particulate matter (PM) concentrations in the size range below 2.5 μm aerodynamic diameter (PM2.5; fine particles). The network peaked at more than 260 sites in 2005. In response to the 1999 Regional Haze Rule and the need to better understand the regional transport of PM, EPA also augmented the long-existing Interagency Monitoring of Protected Visual Environments (IMPROVE) visibility monitoring network in 2000, adding nearly 100 additional IMPROVE sites in rural Class 1 Areas across the country. Both networks measure the major chemical components of PM2.5 using historically accepted filter-based methods. Components measured by both networks include major anions, carbonaceous material, and a series of trace elements. CSN also measures ammonium and other cations directly, whereas IMPROVE estimates ammonium assuming complete neutralization of the measured sulfate and nitrate. IMPROVE also measures chloride and nitrite. In general, the field and laboratory approaches used in the two networks are similar; however, there are numerous, often subtle differences in sampling and chemical analysis methods, shipping, and quality control practices. These could potentially affect merging the two data sets when used to understand better the impact of sources on PM concentrations and the regional nature and long-range transport of PM2.5. This paper describes, for the first time in the peer-reviewed literature, these networks as they have existed since 2000, outlines differences in field and laboratory approaches, provides a summary of the analytical parameters that address data uncertainty, and summarizes major network changes since the inception of CSN.ImplicationsTwo long-term chemical speciation particle monitoring networks have operated simultaneously in the United States since 2001, when the EPA began regular operations of its PM2.5 Chemical Speciation Monitoring Network (IMPROVE began in 1988). These networks use similar field sampling and analytical methods, but there are numerous, often subtle differences in equipment and methodologies that can affect the results. This paper describes these networks since 2000 (inception of CSN) and their differences, and summarizes the analytical parameters that address data uncertainty, providing researchers and policymakers with background information they may need (e.g., for 2018 PM2.5 designation and State Implementation Plan process; McCarthy, 2013) to assess results from each network and decide how these data sets can be mutually employed for enhanced analyses. Changes in CSN and IMPROVE that have occurred over the years also are described.

Haze Formation and the Influence of Ethanol Gasoline of Severe Cold Area on Haze

By analyzing the composition of haze and its formation mechanism, this thesis studies the impact of ethanol gasoline combustion products: aerosol particles, particulate matter, additional products (aldehydes and ketones, etc.) and water on severe cold area regional haze formation. The results show that the effect of ethanol gasoline combustion products on haze formation is also very serious. Therefore, this article does not recommend excessive use of ethanol gasoline in the cold winter.

Submicron aerosols at thirteen diversified sites in China: size distribution, new particle formation and corresponding contribution to cloud condensation nuclei production

Abstract. Understanding the particle number size distributions in diversified atmospheric environments is important in order to design mitigation strategies related to submicron particles and their effects on regional air quality, haze and human health. In this study, we conducted 15 different field measurement campaigns between 2007 and 2011 at 13 individual sites in China, including five urban sites, four regional sites, three coastal/background sites and one ship cruise measurement along eastern coastline of China. Size resolved particles were measured in the 15–600 nm size range. The median particle number concentrations (PNCs) were found to vary in the range of 1.1−2.2 × 104 cm−3 at urban sites, 0.8−1.5 × 104 cm−3 at regional sites, 0.4−0.6 × 104 cm−3 at coastal/background sites, and 0.5 × 104 cm−3 during cruise measurement. Peak diameters at each of these sites varied greatly from 24 to 115 nm. Particles in the 15–25 nm (nucleation mode), 25–100 nm (Aitken mode) and 100–600 nm (accumulation mode) range showed different characteristics at each sites, indicating the features of primary emissions and secondary formation in these diversified atmospheric environments. Diurnal variations show a build-up of accumulation mode particles belt at regional sites, suggesting the contribution of regional secondary aerosol pollution. Frequencies of new particle formation (NPF) events were much higher at urban and regional sites than at coastal sites and during cruise measurement. The average growth rates (GRs) of nucleation mode particles were 8.0–10.9 nm h−1 at urban sites, 7.4–13.6 nm h−1 at regional sites and 2.8–7.5 nm h−1 at coastal sites and during cruise measurement. The high gaseous precursors and strong oxidation at urban and regional sites not only favored the formation of particles, but also accelerated the growth rate of the nucleation mode particles. No significant difference in condensation sink (CS) during NPF days were observed among different site types, suggesting that the NPF events in background areas were more influenced by the pollutant transport. In addition, average contributions of NPF events to potential cloud condensation nuclei (CCN) at 0.2% super-saturation in the afternoon of all sampling days were calculated as 11% and 6% at urban sites and regional sites, respectively. On the other hand, NPF events at coastal sites and during cruise measurement had little impact on potential production of CCN. This study provides a large data set of particle size distribution in diversified atmosphere of China, improving our general understanding of emission, secondary formation, new particle formation and corresponding CCN activity of submicron aerosols in Chinese environments.

Enhanced sulfate formation during China's severe winter haze episode in January 2013 missing from current models

AbstractA regional haze with daily PM2.5 (fine particulate matters with diameters less than 2.5 µm) exceeding 500 µg/m3 lasted for several days in January 2013 over North China, offering an opportunity to evaluate models. Observations show that inorganic aerosols (sulfate, nitrate, and ammonium) are the largest contributor to PM2.5 during the haze period, while sulfate shows the largest enhancement ratio of 5.4 from the clean to haze period. The nested‐grid GEOS‐Chem model reproduces the distribution of PM2.5 and simulates up to 364 µg/m3 of daily maximum PM2.5. Yet on average, the model is a factor of 3 and 4 lower in PM2.5 and fails to capture the large sulfate enhancement from the clean to haze period. A doubling of SO2 emissions over North China, along with daily meteorology corrections, would be required to reconcile model results with surface SO2 observations, but it is not sufficient to explain the model discrepancy in sulfate. Heterogeneous uptake of SO2 on deliquesced aerosols is proposed as an additional source of sulfate under high‐relative humidity conditions during the haze period. Parameterizing this process in the model improves the simulated spatial distribution and results in a 70% increase of sulfate enhancement ratio and a 120% increase in sulfate fraction in PM2.5. Combined adjustments in emissions, meteorology, and sulfate chemistry lead to higher sulfate by a factor of 3 and 50% higher PM2.5, significantly reducing the model's low bias during the haze.

Impact of aerosol–meteorology interactions on fine particle pollution during China’s severe haze episode in January 2013

In January 2013, a severe regional haze occurred over the North China Plain. An online-coupled meteorology-chemistry model was employed to simulate the impacts of aerosol–meteorology interactions on fine particles (PM2.5) pollution during this haze episode. The response of PM2.5 to meteorology change constituted a feedback loop whereby planetary boundary layer (PBL) dynamics amplified the initial perturbation of PM2.5. High PM2.5 concentrations caused a decrease of surface solar radiation. The maximal decrease in daily average solar radiation reached 53% in Beijing, thereby leading to a more stable PBL. The peak PBL height in Beijing decreased from 690 m to 590 m when the aerosol extinction was considered. Enhanced PBL stability suppressed the dispersion of air pollutants, and resulted in higher PM2.5 concentrations. The maximal increase of PM2.5 concentrations reached 140 μg m−3 in Beijing. During most PM2.5 episodes, primary and secondary particles increased simultaneously. These results imply that the aerosol–radiation interactions played an important role in the haze episode in January 2013.

Assessing the regional impact of indonesian biomass burning emissions based on organic molecular tracers and chemical mass balance modeling

Abstract. Biomass burning activities commonly occur in Southeast Asia (SEA), and are particularly intense in Indonesia during the dry seasons. The effect of biomass smoke emissions on air quality in the city state of Singapore was investigated during a haze episode in October 2006. Substantially increased levels of airborne particulate matter (PM) and associated chemical species were observed during the haze period. Specifically, the enhancement in the concentration of molecular tracers for biomass combustion such as levoglucosan by as much as two orders of magnitude and the diagnostic ratios of individual organic compounds indicated that biomass burning emissions caused a regional smoke haze episode due to their long-range transport by prevailing winds. With the aid of air mass backward trajectories and chemical mass balance modeling, large-scale forest and peat fires in Sumatra and Kalimantan were identified as the sources of the smoke aerosol, exerting a significant impact on air quality in downwind areas, such as Singapore.

Burning in agricultural landscapes: an emerging natural and human issue in China

Burning is one of the most widely used methods for removing crop residues during harvest seasons. It cleans fields faster and costs less in comparison to other residue removal methods. Agricultural burning, however, has been recently limited or banned during harvest seasons in China, mainly due to the air quality and human health concerns raised from its use. This paper reviews recent studies on the burning of agricultural landscapes in China to understand the natural (environmental and ecological) and human (economic and social) impacts and identifies uncertainties, gaps, and future research needs. The total annual crop straw output in China is more than 600 billon kg, with about 110, 130, and 230 billion kg coming from rice, wheat, and corn, respectively. Agricultural burning removes about one-fourth of total crop straw and emits about 140–240, 1.6–2.2, and 0.5–0.14 billion kg of CO2, PM2.5, and black carbon, respectively. Agricultural burning accounts for upto half of the total PM10 concentrations in the major burning regions during harvesting periods. Burning emissions contribute to regional haze and smog events. Therefore, limiting or banning agricultural burning is a necessary measure for reducing air pollution in China. The estimations of total burned crop straw amounts and emission factors are the major uncertainty sources for emission estimates. More studies are needed to better describe the smoke plume rise, dispersion, and interactions with weather and climate and to simulate the ecological impacts of agricultural burning. Effective alternatives need to be explored in order to provide solutions for farmers to remove agricultural residues in the wake of the burning ban.

Widespread reductions in haze across the United States from the early 1990s through 2011

Visibility has improved significantly at many remote areas across the United States since the early 1990s. Trends in visibility were calculated using ambient light extinction coefficients (bext) estimated from speciated particulate concentrations measured by the IMPROVE (Interagency Monitoring of Protected Visual Environments) network. The 20% haziest bext levels were computed for each year following Regional Haze Rule guidelines and aggregated over three major regions of the United States. Over the last two decades (1992–2011) the regional mean 20% haziest bext dropped by 52% (−2.6% yr−1, p < 0.01) in the eastern United States, and by 20% (−1.0% yr−1, p = 0.08) for sites along the West Coast. However, in the Intermountain/Southwest region, the trend was insignificant (−0.2% yr−1, p = 0.36). Over the last decade (2002–2011) the haziest bext in the Intermountain/Southwest region decreased by 15% (−1.5% yr−1, p = 0.09), compared to a decrease of 35% (−3.5% yr−1, p = 0.06) in the West Coast region and 50% (−5.0% yr−1, p = 0.02) in the East. A novel aspect to this study is the visualization of trends through the simulation of images of national parks and other remote areas for early and current haziest conditions. These images are an effective means for communicating trends and illustrate the dramatic improvement in visibility, especially in the East, where reductions in sulfate concentrations and sulfur dioxide emissions have had a positive impact on visibility degradation. However, while conditions are clearer for regions in the West, less improvement points to the need for understanding the influences on the trends in haziest conditions in those regions.

Characteristics of secondary inorganic aerosol and sulfate species in size-fractionated aerosol particles in Shanghai

Sulfate, nitrate and ammonium (SNA) are the dominant species in secondary inorganic aerosol, and are considered an important factor in regional haze formation. Size-fractionated aerosol particles for a whole year were collected to study the size distribution of SNA as well as their chemical species in Shanghai. SNA mainly accumulated in fine particles and the highest average ratio of SNA to particulate matter (PM) was observed to be 47% in the fine size fraction (0.49–0.95 μm). Higher sulfur oxidation ratio and nitrogen oxidation ratio values were observed in PM of fine size less than 0.95 μm. Ion balance calculations indicated that more secondary sulfate and nitrate would be generated in PM of fine size (0.49–0.95 μm). Sulfur K-edge X-ray absorption near-edge structure (XANES) spectra of typical samples were analyzed. Results revealed that sulfur mainly existed as sulfate with a proportion (atomic basis) more than 73% in all size of PM and even higher at 90% in fine particles. Sulfate mainly existed as (NH4)2SO4 and gypsum in PM of Shanghai. Compared to non-haze days, a dramatic increase of (NH4)2SO4 content was found in fine particles on haze days only, which suggested the promoting impact of (NH4)2SO4 on haze formation. According to the result of air mass backward trajectory analysis, more (NH4)2SO4 would be generated during the periods of air mass stagnation. Based on XANES, analysis of sulfate species in size-fractionated aerosol particles can be an effective way to evaluate the impact of sulfate aerosols on regional haze formation.

Simulation of GOES-R ABI aerosol radiances using WRF-CMAQ: a case study approach

Abstract. In anticipation of the upcoming GOES-R launch we simulate visible and near-infrared reflectances of the Advanced Baseline Imager (ABI) for cases of high aerosol loading containing regional haze and smoke over the eastern United States. The simulations are performed using the Weather Research and Forecasting (WRF), Sparse Matrix Operator Kernel Emissions (SMOKE), and Community Multiscale Air Quality (CMAQ) models. Geostationary, satellite-derived, biomass-burning emissions are also included as an input to CMAQ. Using the CMAQ aerosol concentrations and Mie calculations, radiance is computed from the discrete ordinate atmospheric radiative transfer model. We present detailed methods for deriving aerosol extinction from WRF and CMAQ outputs. Our results show that the model simulations create a realistic set of reflectances in various aerosol scenarios. The simulated reflectances provide distinct spectral features of aerosols which are then compared to data from the Moderate Resolution Imaging Spectroradiometer (MODIS). We also present a simple technique to synthesize green band reflectance (which will not be available on the ABI), using the model-simulated blue and red band reflectance. This study is an example of the use of air quality modeling in improving products and techniques for Earth-observing missions.

Tribe at a Crossroads: The Navajo Nation Purchases a Coal Mine

Tribe at a Crossroads: The Navajo Nation Purchases a Coal Mine

Intercomparison of Fire Size, Fuel Loading, Fuel Consumption, and Smoke Emissions Estimates on the 2006 Tripod Fire, Washington, USA

AbstractLand managers rely on prescribed burning and naturally ignited wildfires for ecosystem management, and must balance trade-offs of air quality, carbon storage, and ecosystem health. A current challenge for land managers when using fire for ecosystem management is managing smoke production. Smoke emissions are a potential human health hazard due to the production of fine particulate matter (PM2.5), carbon monoxide (CO), and ozone (O3) precursors. In addition, smoke emissions can impact transportation safety and contribute to regional haze issues. Quantifying wildland fire emissions is a critical step for evaluating the impact of smoke on human health and welfare, and is also required for air quality modeling efforts and greenhouse gas reporting. Smoke emissions modeling is a complex process that requires the combination of multiple sources of data, the application of scientific knowledge from divergent scientific disciplines, and the linking of various scientific models in a logical, progressive sequence. Typically, estimates of fire size, available fuel loading (biomass available to burn), and fuel consumption (biomass consumed) are needed to calculate the quantities of pollutants produced by a fire. Here we examine the 2006 Tripod Fire Complex as a case study for comparing alternative data sets and combinations of scientific models available for calculating fire emissions. Specifically, we use five fire size information sources, seven fuel loading maps, and two consumption models (Consume 4.0 and FOFEM 5.7) that also include sets of emissions factors. We find that the choice of fuel loading is the most critical step in the modeling pathway, with different fuel loading maps varying by 108 %, while fire size and fuel consumption show smaller variations (36 % and 23 %, respectively). Moreover, we find that modeled fuel loading maps likely underestimate the amount of fuel burned during wildfires as field assessments of total woody fuel loading were consistently higher than modeled fuel loadings in all cases. The PM2.5 emissions estimates from Consume and FOFEM vary by 37 %. In addition, comparisons with available observational data demonstrate the value of using local data sets where possible.

The 2013 severe haze over southern Hebei, China: model evaluation, source apportionment, and policy implications

Abstract. Extremely severe and persistent haze occurred in January 2013 over eastern and northern China. The record-breaking high concentrations of fine particulate matter (PM2.5) of more than 700 μg m−3 on hourly average and the persistence of the episodes have raised widespread, considerable public concerns. During that period, 7 of the top 10 polluted cities in China were within the Hebei Province. The three cities in southern Hebei (Shijiazhuang, Xingtai, and Handan) have been listed as the top three polluted cities according to the statistics for the first half of the year 2013. In this study, the Mesoscale Modeling System Generation 5 (MM5) and the Models-3/Community Multiscale Air Quality (CMAQ) modeling system are applied to simulate the 2013 severe winter regional hazes in East Asia and northern China at horizontal grid resolutions of 36 and 12 km, respectively, using the Multi-resolution Emission Inventory for China (MEIC). The source contributions of major source regions and sectors to PM2.5 concentrations in the three most polluted cities in southern Hebei are quantified by aiming at the understanding of the sources of the severe haze pollution in this region, and the results are compared with December 2007, the haziest month in the period 2001–2010. Model evaluation against meteorological and air quality observations indicates an overall acceptable performance and the model tends to underpredict PM2.5 and coarse particulate matter (PM10) concentrations during the extremely polluted episodes. The MEIC inventory is proven to be a good estimation in terms of total emissions of cities but uncertainties exist in the spatial allocations of emissions into fine grid resolutions within cities. The source apportionment shows that emissions from northern Hebei and the Beijing-Tianjin city cluster are two major regional contributors to the pollution in January 2013 in Shijiazhuang, compared with those from Shanxi and northern Hebei for December 2007. For Xingtai and Handan, the emissions from northern Hebei and Henan are important. The industrial and domestic sources are the most significant local contributors, and the domestic and agricultural emissions from Shandong and Henan are non-negligible regional sources, especially for Xingtai and Handan. Even in the top two haziest months (i.e., January 2013 and December 2007), a large fraction of PM2.5 in the three cities may originate from quite different regional sources. These results indicate the importance of establishing a regional joint framework of policymaking and action system to effectively mitigate air pollution in this area, not only over the Beijing-Tianjin-Hebei area, but also surrounding provinces such as Henan, Shandong, and Shanxi.

Haze in China: Current and future challenges

Regional haze which triggered both public anxiety and official concerns has been one of the most disastrous weather events in China in recent years. Haze not only had negative impact on daily life, but also an indicator of high concentrations of PM2.5 with the potential to adversely impact public health by damaging people's respiratory, cardiovascular, blood vessel of brain and nervous system. The dust-haze is an accumulated result for a long time of both natural factors and unhealthy economic growth model. In order to tackle air pollution, a number of policies and measures which target at reducing pollution emission and promoting alternative energy production had been implemented. Although significant improvement has occurred in China, change the development mode of “high growth, high pollution” and balance environmental conservation with the well-being of the population remains a challenge for China.

A multisource observation study of the severe prolonged regional haze episode over eastern China in January 2013

By employing visibility observation, PM10, SO2 and NO2 concentration, MODIS AOD at 550 nm, CARSNET AOD at 440 nm, CALIPSO extinction coefficient at 532 nm, we studied the air pollution condition of a severe haze episode occurred on 6–16 January 2013 over eastern China. The study found that this severe pollution episode of large area haze was accompanied with low visibility, high PM10 and AOD in eastern China. The most polluted regions is the Jing-Jin-Ji and its near southern neighboring region including central and south Hebei, west Shandong and north Henan province in the whole China Mainland. The haze pollutants were spread to the offshore area of 125°E to the east of China, and even affected to the west of 140°E. The PM10 variation trend shows a strong linkage among the big cities in Jing-Jin-Ji and their near surrounding cities, indicating the possible inter-transport and influence among them. The suburb area of megacity suffered the similar serious pollution with urban region during this kind of severe haze episode. Most aerosol pollutants concentrated in boundary layer below 1500 m vertical height, in particular, the vertical heights of 100–800 m above the ground are peaks of the aerosol pollutants.

Comparison of MODIS 3 km and 10 km resolution aerosol optical depth retrievals over land with airborne sunphotometer measurements during ARCTAS summer 2008

Abstract. Airborne sunphotometer measurements acquired by the NASA Ames Airborne Tracking Sunphotometer (AATS-14) aboard the NASA P-3 research aircraft are used to evaluate dark-target over-land retrievals of extinction aerosol optical depth (AOD) from spatially and temporally near-coincident measurements by the Moderate Resolution Imaging Spectroradiometer (MODIS) during the summer 2008 Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) field campaign. The new MODIS Collection 6 aerosol data set includes retrievals of AOD at both 10 km × 10 km and 3 km × 3 km (at nadir) resolution. In this paper we compare MODIS and AATS AOD at 553 nm in 58 10 km and 134 3 km retrieval grid cells. These AOD values were derived from data collected over Canada on four days during short time segments of five (four Aqua and one Terra) satellite overpasses of the P-3 during low-altitude P-3 flight tracks. Three of the five MODIS–AATS coincidence events were dominated by smoke: one included a P-3 transect of a well-defined smoke plume in clear sky, but two were confounded by the presence of scattered clouds above smoke. The clouds limited the number of MODIS retrievals available for comparison, and led to MODIS AOD retrievals that underestimated the corresponding AATS values. This happened because the MODIS aerosol cloud mask selectively removed 0.5 km pixels containing smoke and clouds before the aerosol retrieval. The other two coincidences (one Terra and one Aqua) occurred during one P-3 flight on the same day and in the same general area, in an atmosphere characterized by a relatively low AOD (&lt; 0.3), spatially homogeneous regional haze from smoke outflow with no distinguishable plume. For the ensemble data set for MODIS AOD retrievals with the highest-quality flag, MODIS AOD agrees with AATS AOD within the expected MODIS over-land AOD uncertainty in 60% of the retrieval grid cells at 10 km resolution and 69% at 3 km resolution. These values improve to 65 % and 74%, respectively, when the cloud-affected case with the strongest plume is excluded. We find that the standard MODIS dark-target over-land retrieval algorithm fails to retrieve AOD for thick smoke, not only in cloud-contaminated regions but also in clear sky. We attribute this to deselection, by the cloud and/or bright surface masks, of 0.5 km resolution pixels that contain smoke.

Air quality modeling in East Asia: present issues and future directions

The rapid economic growth has increased trace gas emissions in East Asia, resulting in various environmental issues, including acid deposition, regional haze, air quality degradation, and climate change, which are critical to the human existence. In particular, air quality degradation became an object of rising concern in East Asian countries. In order to understand sources, transport, and chemical transformation of air pollutants, scientists have widely used atmospheric chemical transport models (CTMs) in East Asia. Here we review our knowledge related to the present air quality issues and their modeling, focusing on O3 and particulate matter in East Asia. We finally suggest a few recommendations for the next generation of air quality models to improve their capability and use in this region.

Determination of organic matter and organic matter to organic carbon ratios by infrared spectroscopy with application to selected sites in the IMPROVE network

Mass of ambient particulate organic matter (OM) is often estimated by multiplying the organic carbon (OC) mass by a fixed factor that typically ranges from 1.4 to 1.8. In this paper, we develop a non-destructive, mid-infrared spectroscopic (MIR) technique to measure OM in PM2.5 collected on PTFE filters (commonly called “teflon” filters). MIR techniques measure absorption by functional groups within organic molecules; that is, carbon atoms bonded to oxygen (O) or hydrogen (H), O bonded to H and other elements bonded together in organic molecules that comprise OM. We developed laboratory standards of atmospherically relevant organic compounds as the basis for calibrating the MIR absorption to the moles of functional groups. A multivariate regression technique was used to develop calibrations for quantifying alkane CH, alcohol OH, carboxylic acid OH, and carbonyl, which likely comprise the bulk of OM in most ambient samples. OM is estimated as the sum of masses attributed to these functional groups. The precision of the OM measurement is 6.9 μg (relative precision is 7%) and the minimum detection limit is 4.8 μg, corresponding to an ambient concentrations of 0.21 μg m−3 and 0.15 μg m−3 respectively, for the sampling protocol used here.The method was employed to estimate OM, OC (estimated as the sum of the mass of carbon in the alkane CH and carbonyl functional groups) and OM/OC from one year of routinely collected filters at seven Interagency Monitoring of Protected Visual Environments (IMPROVE) sites. In the IMPROVE network, OC is measured using a thermal optical method and OM is estimated for regional haze tracking simply as 1.8 × OC. Using the MIR technique on one year of samples from 7 IMPROVE sites, the median OM/OC ratio was 1.69 with the 10th and 90th percentiles of 1.46 and 2.01. Phoenix, AZ had the lowest annual-median value of 1.56 and Mesa Verde, CO had the highest of 1.83. For more than half of the sites, the lowest monthly-median OM/OC ratio occurred in winter. The sample, site median and seasonal median OM/OC ratios obtained from MIR analysis indicate that a single estimate of OM/OC does not represent the observed variability in OM/OC.