PM10 Observed at a Meteorological Station in Beijing: Historical Trend and Implications

Inhalable particles (PM10), with aerodynamic equivalent diameters that are generally 10 micrometers or smaller, are basic pollutants in many areas, especially in northern China, and thus the pollution from PM10 inhalable particulate matter is a growing concern for public health. Independent long-term observations are necessary to evaluate the efficacy of PM10 reduction actions. Variations in the PM10 concentration from 2006 to 2017 at an observation station (NJ) in Beijing were recorded and analyzed. The average value ±1 standard deviation of daily mean PM10 concentrations was 138.8 ±96.1 μg m-3 for 1307 days (accounting for 34.7% of the total days), showing PM10 concentration exceeding the National Ambient Air Quality Standard (NAAQS) 24-h average of 150 μg m-3. Particulate concentration depended upon various meteorological conditions as also observed in this work: at low wind speed (<4 m s-1), the concentrations of PM10 revealed a downward trend with -19 μg m-3 per unit of wind speed, but when wind speed rose (>4 m s-1), the values increased by 49 μg m-3 per unit of wind speed. In Beijing, air masses from northwest China, especially from the Gobi Desert and other desert areas, had net contributions to long-range transport of natural dust, enhancing the PM10 concentrations by up to 29%. Overall, PM10 mass concentration showed a significant downward trend with -8.0 μg/m3/yr from 2006 to 2017. Although with higher fluctuations in recorded data, similar downward trends derived from the ) in 2017 still exceeded the NAAQS standard. The results showed that there is still a long way to go to reduce PM10 in Beijing.     

Characteristics of Elemental Composition of PM2.5 in the Spring Period at Tongyu in the Semi-arid Region of Northeast China

Continuous observations of mass concentration and elemental composition of aerosol particles （PM2.5） were conducted at Tongyu, a semi-arid site in Northeast China in the spring of 2006. The average mass concentration of PM2.5 at Tongyu station was 260.9±274.4 μg m^-3 during the observation period. Nine dust events were monitored with a mean concentration of 528.0±302.7 μgm^-3. The PM2.5 level during non- dust storm （NDS） period was 111.65±63.37 μg m^-3. High mass concentration shows that fine-size particles pollution was very serious in the semi-arid area in Northeast China. The enrichment factor values for crust elements during the dust storm （DS） period are close to those in the NDS period, while the enrichment factor values for pollution elements during the NDS period are much higher than those in the DS period, showing these elements were from anthropogenic sources. The ratios of dust elements to Fe were relative constant during the DS period. The Ca/Fe ratio in dust aerosols at Tongyu is remarkably different from that observed in other source regions and downwind regions. Meteorological analysis shows that dust events at Tongyu are usually associated with dry, low pressure and high wind speed weather conditions. Air mass back-trajectory analysis identified three kinds of general pathways were associated with the aerosol particle transport to Tongyu, and the northwest direction pathway was the main transport route.     

Comparative inverse analysis of satellite (MODIS) and ground (PM10) observations to estimate dust emissions in East Asia

Soil dust aerosol is the largest contributor to aerosol mass concentrations in the troposphere and has considerable effects on air quality and climate. Arid and semi-arid areas of East Asia are one of the important dust source regions thus it is crucial to understand dust mobilization and accurately estimate dust emissions in East Asia. However, present dust models still contain large uncertainties with dust emissions that remain a significant contributor to the overall uncertainties in the model. In this study, we attempt to reduce these uncertainties by using an inverse modeling technique and obtain optimized dust emissions. We use Moderate Resolution Imaging Spectrometer (MODIS) aerosol optical depths (AODs) and groundbased mass concentrations of particles less than 10 μm in aerodynamic diameter (PM₁₀) observations over East Asia in May 2007. The MODIS AODs are validated with AErosol RObotic NETwork (AERONET) AODs. The inversion uses the maximum a posteriori method and the GEOS-Chem chemical transport model (CTM) as a forward model. The model error is large over dust source regions including the Gobi Desert and Mongolia. We find that inverse modeling analyses from the MODIS and PM₁₀ observations consistently result in decrease of dust emissions over Mongolia and the Gobi Desert. Whereas over the Taklamakan Desert and Manchuria, the inverse modeling analyses from both observations yield contrast results such as increase of dust sources using MODIS AODs, while decrease of those using PM₁₀ observations. We discuss some limitations of both observations to obtain the optimized dust emissions and suggest several strategies for the improvement of dust emission estimates in the model.     

A Modeling Study of Seasonal Variation of Atmospheric Aerosols over East Asia

In this study, a regional air quality model system (RAQMS) was applied to investigate the spatial distributions and seasonal variations of atmospheric aerosols in 2006 over East Asia. Model validations demonstrated that RAQMS was able to reproduce the evolution processes of aerosol components reasonably well. Ground-level PM₁₀ (particles with aerodynamic diameter ≤10 μm) concentrations were highest in spring and lowest in summer and were characterized by three maximum centers: the Taklimakan Desert (～1000 μg m^-3), the Gobi Desert (～400 μg m^-3), and the Huabei Plain (～300 μm^-3) of China. Vertically, high PM₁₀ concentrations ranging from 100 μg m^-3 to 250 μg m^-3 occurred from the surface to an altitude of 6000 m at 30^o--45^oN in spring. In winter, the vertical gradient was so large that most aerosols were restricted in the boundary layer. Both sulfate and ammonium reached their highest concentrations in autumn, while nitrate reached its maximum level in winter. Black carbon and organic carbon aerosol concentrations reached maximums in winter. Soil dust were strongest in spring, whereas sea salt exerted the strongest influence on the coastal regions of eastern China in summer. The estimated burden of anthropogenic aerosols was largest in winter (1621 Gg) and smallest in summer (1040 Gg). The sulfate burden accounted for ～42% of the total anthropogenic aerosol burden. The dust burden was about twice the anthropogenic aerosol burden, implying the potentially important impacts of the natural aerosols on air quality and climate over East Asia.     

Long-term size-segregated particle (PM10, PM2.5, PM1) characterization study at Melpitz -- influence of air mass inflow, weather conditions and season

Size-segregated high-volume (HV) quartz filter samples were collected daily at the Melpitz rural site in Germany for PM₁₀ (November 1992 until April 2012), and for PM_2.5 and PM₁ (January 2003 until April 2012, PM₁ sampled every sixth day). The samples were analysed for mass concentration (gravimetrically), water-soluble ions (ion-chromatography) and since 2003 for organic carbon (OC) and elemental carbon (EC) (thermography). The long-term measurements first show a decreasing trend for PM₁₀ (1993–2000) followed by a second period (2001–2011) with a mean mass concentration of about 22.4 μgm^?3 and an inter-annual variation of about?±?2.9 μgm^?3 (13% fluctuation margin). The absolute sulphate and calcium concentration (for the full period), as well as the EC concentration (time after 2003) decrease by about 50, 75 and 30% for PM₁₀, respectively. The nitrate concentration remains constant all the time. For the daily objective weather type classification (OWTC, 1993–2002) the highest PM₁₀ concentration was found for South-East (SE) and the lowest for North-West (NW) wind direction with 44 and 24 μgm^?3, respectively. These concentrations decrease for 2003–2011 in comparison to 1993–2002 by about 21% and 26%, respectively. The highest PM₁₀, PM_2.5 and PM₁ concentrations (2003–2011) were found for SE and the lowest for NW wind direction with about 34 and 17 μgm^?3 (PM₁₀), 28 and 19 μgm^?3 (PM_2.5) and 22 and 11 μgm^?3 (PM₁), respectively. The relative content of sulphate, OC and EC was the highest for SE wind direction. A differentiation into four categories for winter (Wi) and summer (Su) and air mass inflow from West (W) and East (E) was carried out. The highest PM concentrations were observed for WiE with the highest inter-annual fluctuation. In this category sulphate contents are largest. The lowest concentrations where found for SuW. The means for WiE show the strongest relative decreases, e.g. in PM₁₀ sulphate (1993–2011) and EC (2003–2011) by about 60% and 40%, respectively. Nitrate is an indicator for NO_x motor-car emissions. It shows a typical variation with maximum values in the middle of the week_, especially for air mass inflow from West. In contrast, chloride mostly originating from sea spray doesn’t show such a concentration pattern. The PM_2.5/PM₁₀ as well the PM₁/PM₁₀-ratio have the highest median (0.878 and 0.654) during WiE and the lowest (0.718 and 0.578) during SuW, respectively. For the ratio PM_2.5/PM₁₀ a slightly increasing trend was found (about 0.71 and 0.83 for 1995 and 2011, respectively). The increase is stronger in summer than in winter.     

Impact of a dust storm on characteristics of particle matter (PM) in Guangzhou, China

A strong dust-storm (23–25 April, 2009) occurred in the provinces of Inner Mongolia, Gansu, and Shanxi, North China. Cities along the storm path (from north to south: Xi’ning, Lanzhou, Chengdu, Changsha, and Guangzhou) all experienced a sharp increase in particle matter (PM₁₀) concentration. This is the first case that an Asian dust storm hit Guangzhou in Southern China. The impacts of dust storm on the characteristics of PM were investigated using samples collected in Guangzhou during 27–29 April, 2009. In addition, the mass concentration and chemical composition during a normal non-dust period (12–14 May, 2009) were compared with those in dust period. The results show that the concentration of PM₁₀ during the dust episode (0.231 mg m^?3) was twice higher than that in the non-dust episode (0.103 mg m^?3). Chemical analysis showed that concentrations of metal elements, enrichment factors of metal elements, and soluble ions during the dust episode were very different from those of non-dust. The total concentration of metal elements content in PM₁₀ was 53.5 μg m^?3 in the dust episode, which is about two times higher than that in non-dust episode (28.5 μg m^?3). Increases in concentrations of Na, Ti, Zn, Cu, and Cr ranged from zero to 100% during the dust episode. However, the enrichment factors in non-dust episode were higher than that in dust-storm period, indicating that the above five chemicals originated mainly from local sources in Guangzhou. The concentrations of K, Mg, Al, Fe, Mn, V, and Co increased by over 100% in the dust episode, indicating their origins of remote sources. In the dust period, some water-soluble ions increased in PM₁₀, but the main components in PM₁₀ were SO₄ ^?, NO₃ ^? and NH₄ ⁺. At last, we assessed the sources of dusts by analyzing synoptic situation and back trajectories of air mass in Guangzhou, and demonstrated that the main source of the dust storm was from Mongolia.     

Stable carbon and nitrogen isotopic characteristics of PM2.5 and PM10 in Delhi,India

This study presents the chemical composition (carbonaceous and nitrogenous components) of aerosols (PM_2.5 and PM₁₀) along with stable isotopic composition (δ¹³C and δ¹⁵N) collected during winter and the summer months of 2015–16 to explore the possible sources of aerosols in megacity Delhi, India. The mean concentrations (mean?±?standard deviation at 1σ) of PM_2.5 and PM₁₀ were 223?±?69 µg m^?3 and 328?±?65 µg m^?3, respectively during winter season whereas the mean concentrations of PM_2.5 and PM₁₀ were 147?±?22 µg m^?3 and 236?±?61 µg m^?3, respectively during summer season. The mean value of δ¹³C (range: ??26.4 to ??23.4‰) and δ¹⁵N (range: 3.3 to 14.4‰) of PM_2.5 were ??25.3?±?0.5‰ and 8.9?±?2.1‰, respectively during winter season whereas the mean value of δ¹³C (range: ??26.7 to ??25.3‰) and δ¹⁵N (range: 2.8 to 11.5‰) of PM_2.5 were ??26.1?±?0.4‰ and 6.4?±?2.5‰, respectively during the summer season. Comparison of stable C and N isotopic fingerprints of major identical sources suggested that major portion of PM_2.5 and PM₁₀ at Delhi were mainly from fossil fuel combustion (FFC), biomass burning (BB) (C-3 and C-4 type vegitation), secondary aerosols (SAs) and road dust (SD). The correlation analysis of δ¹³C with other C (OC, TC, OC/EC and OC/WSOC) components and δ¹⁵N with other N components (TN, NH₄⁺ and NO₃^?) are also support the source identification of isotopic signatures.

     

2010年民勤沙地近地面沙尘气溶胶浓度特征

为了更好地研究沙尘气溶胶起沙和输送特征,2010年4—5月,在民勤周边沙地利用EZ LIDAR ALS300&ALS450型激光雷达和 GRIMM 180型颗粒物采样器进行了大气气溶胶的外场连续观测,取得了晴天、浮尘、扬沙和沙尘暴天气条件下沙尘气溶胶总后向散射垂直剖面图和PM₁₀、PM_2.5、PM_1.0质量浓度采样资料,其中包含“0424”特强沙尘暴过程资料。结果表明：春季民勤近地层大气中沙尘气溶胶浓度较高,且随气象要素的变化很大;在整个观测期内,PM₁₀、PM_2.5、PM_1.0的平均质量浓度分别为202.3、57.4 μg/m³、16.7 μg/m³。在不同天气条件下,PM₁₀、PM_2.5、PM_1.0质量浓度的变化有很好的相关性,但变化趋势有所不同。在沙尘暴天气条件下,PM₁₀的日平均质量浓度高达2469.1μg/m³,是背景天气条件下PM10日平均质量浓度的100多倍,是浮尘天气条件下PM10日平均质量浓度的8倍,是扬沙天气条件下PM₁₀日平均质量浓度的2倍。PM_2.5在沙尘暴天气下日平均质量浓度为460.3 μg/m³,是背景天气条件下PM_2.5日平均质量浓度的45倍,是浮尘天气条件下PM_2.5日平均质量浓度的6倍,是扬沙天气条件下PM_2.5日平均质量浓度的1.4倍。PM_1.0在沙尘暴天气条件下的日平均浓度为92.7 μg/m³,是背景天气条件下PM_1.0日平均浓度的13倍,是浮尘天气条件下PM_1.0日平均浓度的7倍,是扬沙天气条件下PM_1.0日平均浓度的1.3倍。可见,风速增大时沙尘粒子浓度的增加对粒子粒径是有选择的,小粒子比重随沙尘浓度增加而相对减小,大粒子比重随沙尘浓度增加而相对增多;通过对“0424”特强沙尘暴过程的研究表明,一次沙尘暴过程往往包括沙尘暴、扬沙和浮尘天气中的两种类型;通过对激光雷达数据分析发现,在强沙尘暴发生过程当中,民勤沙地发生了非常严重的风蚀起沙现象。     

Numerical simulation and evaluation of Asian dust events observed in Mongolia in spring 2011

The Asian dust forecasting model, Mongolian Asian Dust Aerosol Model (MGLADAM), has been operated by the National Agency for Meteorology and Environmental Monitoring of Mongolia since 2010, for the forecast of Asian dust storms. In order to evaluate the performance of the dust prediction model, we simulated Asian dust events for the period of spring 2011. Simulated features were compared with observations from two sites in the dust source region of the Gobi desert in Mongolia, and in the downstream region in Korea. It was found that the simulated wind speed and friction velocity showed a good correlation with observations at the Erdene site (one of the sites in the Gobi desert). The results show that the model is proficient in the simulation of dust concentrations that are within the same order of magnitude and have similar start and end times, compared with PM₁₀ observed at two monitoring sites in the Gobi regions. Root Mean Square Error (RMSE) of the dust simulation ranges up to 200 μg m^?3 because of the high concentrations in source regions, which is three times higher than that in the downstream region. However, the spatial pattern of dust concentration matches well with dust reports from synoptic observation. In the downwind regions, it was found that the model simluated all reported dust cases successfully. It was also found that the RMSE in the downwind region increased when the model integration time increased, but that in the source regions did not show consistent change. It suggests that MGLADAM has the potential to be used as an operational dust forecasting model for predicting major dust events over the dust source regions as well as predicting transported dust concentrations over the downstream region. However, it is thought that further improvement in the emission estimation is necessary, including accurate predictions in surface and boundary layer meteorology. In the downwind regions, background PM₁₀ concentration is considerably affected by other aerosol species, suggesting that a consideration of anthropogenic pollutants will be required for accurate dust forecasting.     

The aerosol radiative effect on a severe haze episode in the Yangtze River Delta

Due to increased aerosol emissions and unfavorable weather conditions, severe haze events have occurred frequently in China in the last 10 years. In addition, the interaction between the boundary layer and the aerosol radiative effect may be another important factor in haze formation. To better understand the effect of this interaction, the aerosol radiative effect on a severe haze episode that took place in December 2013 was investigated by using two WRF-Chem model simulations with different aerosol configurations. The results showed that the maximal reduction of regional average surface shortwave radiation, latent heat, and sensible heat during this event were 88, 12, and 37 W m^–2, respectively. The planetary boundary layer height, daytime temperature, and wind speed dropped by 276 m, 1°C, and 0.33 m s^–1, respectively. The ventilation coefficient dropped by 8%–24% for in the central and northwestern Yangtze River Delta (YRD). The upper level of the atmosphere was warmed and the lower level was cooled, which stabilized the stratification. In a word, the dispersion ability of the atmosphere was weakened due to the aerosol radiative feedback. Additional results showed that the PM_2.5 concentration in the central and northwestern YRD increased by 6–18 μg m^–3, which is less than 15% of the average PM_2.5 concentration during the severely polluted period in this area. The vertical profile showed that the PM_2.5 and PM₁₀ concentrations increased below 950 hPa, with a maximum increase of 7 and 8 μg m^–3, respectively. Concentrations reduced between 950 and 800 hPa, however, with a maximum reduction of 3.5 and 4.5 μg m^–3, respectively. Generally, the aerosol radiative effect aggravated the level of pollution, but the effect was limited, and this haze event was mainly caused by the stagnant meteorological conditions. The interaction between the boundary layer and the aerosol radiative effect may have been less important than the large-scale static weather conditions for the formation of this haze episode.     

A simulation of Asian dust events observed from 20 to 29 December 2009 in Korea by using ADAM2

The Asian dust Aerosol Model 2 (ADAM2) with the MM5 meteorological model has been employed to study long-range transport process of Asian dust and to estimate dust emission, deposition (wet and dry) and concentration over the Asian dust source region and the downwind regions for dust events observed in Korea during the period of 20–29 December 2009, which is one of the dust events chosen by the 3^rd Meeting of Working Group for Joint Research on Dust Sand Storm among Mongolia, China, Japan and Korea to study intensively for the development of an early warning system in Asia. It is found that the model simulates quite well the starting and ending times of dust events and the peak dust concentrations with their occurrence times both in the source region and downwind regions. The dust emission in the dust source region is found to be associated with a developing synoptic weather system accompanied with strong surface winds over the source region that usually travels east to southeastward across the source region and then turns to move northeastward toward the north western Pacific Ocean. The dust emitted in the source region is found to be split into two parts: one is transported southeastward to the East China Sea in front of the surface high pressure system and experiencing enhanced deposition due to the sinking motion induced by the southeastward traveling the surface high pressure system whereas, the other moves northeastward toward the surface low pressure system and then lifted upward to form a upper-level high dust concentration layer that results in a favorable condition for the long-range transport of dust. It is also found that the maximum ten-day total dust emission of about 23 t km^?2 occurs in the domain Northwestern China (NWC). However, the maximum ten-day total dust deposition of 21 t km^?2 with the maximum mean surface concentration of 555 μg m^?3 and the column integrated mean concentration of 2.9 g m^?2 occurs in the domain Central-northern China (CNC). The column-integrated PM₁₀ concentration is found to increase toward northeastward especially in the domain North northeastern China (NNEC) due to the upper-level transported high PM₁₀ concentration. The ten-day total dust deposition, mean surface PM₁₀ and column integrated PM₁₀ concentrations in the downwind domains are found to decrease away from the source region from 2.44 t km^?2, 112 μg m^?3 and 1.68 g m^?2, respectively in the domain YES to 0.06 t km^?2, 2.1 μg m^?3 and 0.4 g m^?2, respectively in the domain Northwestern Pacific 1 (NWP1). Much of the total dust deposition is largely contributed by wet deposition in the far downwind region of the seas while that is contributed by dry deposition in the source region.     

Seasonal variation of water-soluble inorganic components in aerosol size-segregated at the puy de D?me station (1,465?m?a.s.l.), France

The size-segregated chemical composition of aerosol particles was investigated during 1?year at the puy de D?me (1,465?m?a.s.l.), France. These measurements aimed to a better understanding of the influence of the air mass origin on the size-segregated chemical composition of the aerosol at an altitude site. Mountain site measurements are important because they are representative of long range transport and useful for model validation. PM₁ mass concentration exhibits a seasonal variability with a summer maximum. The composition of PM₁ did not change significantly in terms of relative contribution of water soluble inorganic ions but is rather variable in term of total mass concentrations. For the PM_10-1, a different seasonal behaviour was found with maxima concentrations in autumn-winter. Aerosols were classified into four different categories according to their air mass origin: marine, marine modified, continental and Mediterranean. The PM₁₀ aerosol mass at 50?% relative humidity was close to 2.5???g?m^?3 in the marine, 4.3???g?m^?3 in the marine modified, 10.3???g?m^?3 in the continental and 7.7???g?m^?3 in the Mediterranean sectors. We noted that the influence of the air mass origin (on the chemical properties) could be seen especially on the PM_10-1. A significant PM_10-1 mode was found in marine, modified marine, and Mediterranean air masses, and PM₁ dominated in the continental air masses samples. As a result, the aerosol chemical composition variability at the puy de D?me is a function of both the season and air mass type and we provide a chemical composition of the aerosol as a function of each of these environmental factors.     

Characteristics of carbonaceous particles in Beijing during winter and summer 2003

Campaigns were conducted to measure Organic Carbon (OC) and Elemental Carbon (EC) in PM2.5 during winter and summer 2003 in Beijing. Modest differences of PM2.5 and PM10 mean concentrations were observed between the winter and summer campaigns. The mean PM2.5/PM10 ratio in both seasons was around 60%, indicating PM2.5 contributed significantly to PM10. The mean concentrations of OC and EC in PM2.5 were 11.2±7.5 and 6.0±5.0μg m-3 for the winter campaign, and 9.4±2.1 and 4.3±3.0 μg m-3 for the summer campaign, respectively. Diurnal concentrations of OC and EC in PM2.5 were found high at night and low during the daytime in winter, and characterized by an obvious minimum in the summer afternoon. The mean OC/EC ratio was 1.87±0.09 for winter and Z39±0.49 for summer. The higher OC/EC ratio in summer indicates some formation of Secondary Organic Carbon (SOC). The estimated SOC was 2.8 μg m-3 for winter and 4.2μg m-3 for summer.     

塔里木盆地沙尘气溶胶的柱质量密度特性

气溶胶质量密度是气溶胶重要的参数,它影响着大气中复杂的化学反应,也与气溶胶的传输过程和空间分布息息相关.基于MERRA-2再分析资料提供的气溶胶柱质量密度数据,研究了我国塔里木盆地1980—2018年长时间序列的沙尘气溶胶柱质量密度的时空分布特征.结果表明,沙尘气溶胶和沙尘PM_2.5气溶胶柱质量密度有很大的变化范围,平均值分别为0.33和0.086 g/m²,同时具有明显的年际、月和季节变化特征.沙尘气溶胶和沙尘PM_2.5气溶胶柱质量密度的年平均值在0.24~0.41和0.06~0.11 g/m²范围内变化;春季最大,其平均值分别为0.47和0.12 g/m²,冬季最小,其平均值分别为0.13和0.04 g/m²;月平均值最大出现在5月,分别为0.57和0.14 g/m²,最小在1月,分别为0.1和0.03 g/m².     

Study of seasonal variation of PM2.5 concentration associated with meteorological parameters at residential sites in Delhi,India

The seasonal variation of particulate matter and its relationship with meteorological parameters were measured at five different residential sites in Delhi. Sampling was carried out for one year including all three seasons (summer, monsoon, and winter). The yearly average concentration of particulate matter (PM_2.5) was 135.16 ± 41.34 µg/m³. The highest average values were observed in winter (208.44 ± 43.67 µg/m³) and the lowest during monsoon season (80.29 ± 39.47 µg/m³). The annual average concentration of PM_2.5 was found to be the highest at the Mukherjee Nagar site (242.16 µg/m³ ) during the winter and lowest at (Jawaharlal Nehru University) JNU (35.65 µg/m³) during the monsoon season. The strongest correlation between PM mass and a meteorological parameter was a strong negative correlation with temperature (R2=0.55). All other parameters were weakly correlated (R2<0.2) with PM mass.

     

The Asian Dust Aerosol Model 2 (ADAM2) with the use of Normalized Difference Vegetation Index (NDVI) obtained from the Spot4/vegetation data

The operational Asian Dust Aerosol Model (ADAM)1 in Korea Meteorological Administration has been modified to the ADAM2 model to be used as an operational forecasting model all year round not only in Korea but also in the whole Asian domain (70-160°E and 5-60°N) using the routinely available World Meteorological Organization (WMO) surface reporting data and the Spot/vegetation Normalized Difference Vegetation Index (NDVI) data for the period of 9 years from 1998 to 2006. The 3-hourly reporting WMO surface data in the Asian domain have been used to re-delineate the Asian dust source region and to determine the temporal variation of the threshold wind speed for the dust rise. The dust emission reduction factor due to vegetation in different surface soil-type regions (Gobi, sand, loess, and mixed soil) has been determined with the use of NDVI data. It is found that the threshold wind speed for the dust rise varies significantly with time (minimum in summer and maximum in winter) and surface soil types with the highest threshold wind speed of 8.0 m?s^?1 in the Gobi region and the lowest value of 6.0 m?s^?1 in the loess region. The statistical analysis of the spot/vegetation NDVI data enables to determine the emission reduction factor due to vegetation with the free NDVI value that is the NDVI value without the effect of vegetation and the upper limit value of NDVI for the dust rise in different soil-type regions. The modified ADAM2 model has been implemented to simulate two Asian dust events observed in Korea for the periods from 31 March to 2 April 2007 (a spring dust event) and from 29 to 31 December 2007 (a winter dust event) when the observed PM₁₀ concentration at some monitoring sites in the source region exceeds 9,000 μg m^?3. It is found that ADAM2 model successfully simulates the observed high dust concentrations of more than 8,000 μg m^?3 in the dust source region and 600 μg m^?3 in the downstream region of Korea. This suggests that ADAM2 has a great potential for the use of an operational Asian dust forecast model in the Asian domain.     

The comparison of two severe Hwangsa (Asian dust) cases of spring and winter in Seoul, Korea

This study investigated meteorological, physical, and chemical characteristics of 2 severe Hwangsa (Asian dust, maximum average of PM₁₀ above 1000 μg m^?3) observed in Seoul, the capital city of Korea, during 30～31^st May, 2008 (DSS2008) and 25～26^th December, 2009 (DSS2009). DSS2008 and DSS2009 had a same source region and route. However, they have different meteorological conditions. DSS2009 had a shorter travel time from the source region to Korea and shorter duration time in Korea than DSS2008 due to a strong winter Siberian anticyclone. One of DSS2008 sample was affected by not only Asian dust but also a long-range transported haze due to consecutive influx after low pressure passed while DSS2009 sample collected only dust aerosol. For both cases, the mass concentration of coarse particles (PM_10-1) increased by 3～14 times compared to that during non Asian dust period, however, that of fine particles (PM₁) increased only in DSS2008. For DSS2008 water-soluble ion balance between anions and cations in fine mode was close to 1:1 while cations were higher than anions in coarse mode. NH₄ ⁺ and Ca²⁺ were found to be the main contributing factors for the neutralization. Cl^? loss was observed about 60% indicating an active interaction of Na⁺ with pollutants. Reconstruction of chemical compositions showed relatively high concentrations of secondary pollutants (NH₄NO₃ and (NH₄)₂SO₄), CaCO₃, and Ca(NO₃)₂ compared to that during non Asian dust period. DSS2009 exhibited the typical characteristics of Asian dust having a high concentration of Ca²⁺ with higher equivalent concentration of cations than anions in all size bins. Cl^? loss was hardly observed. The secondary pollutants were lower than that of non Asian dust cases. The result of reconstruction of ionic components indicated the CaCO₃ derived from soil particle, CaSO₄, and Ca (NO₃)₂ were dominant in DSS2009.     

Atmospheric ionic species in PM2.5 and PM1 aerosols in the ambient air of eastern central India

This study elucidates the characteristics of ambient PM_2.5 (fine) and PM₁ (submicron) samples collected between July 2009 and June 2010 in Raipur, India, in terms of water soluble ions, i.e. Na⁺, NH ₄ ⁺ , K⁺, Mg²⁺, Ca²⁺, Cl^?, NO ₃ ^? and SO ₄ ^2? . The total number of PM_2.5 and PM₁ samples collected with eight stage cascade impactor was 120. Annual mean concentrations of PM_2.5 and PM₁ were 150.9?±?78.6 μg/m³ and 72.5?±?39.0 μg/m³, respectively. The higher particulate matter (PM) mass concentrations during the winter season are essentially due to the increase of biomass burning and temperature inversion. Out of above 8 ions, the most abundant ions were SO ₄ ^2? , NO ₃ ^? and NH ₄ ⁺ for both PM_2.5 and PM₁ aerosols; their average concentrations were 7.86?±?5.86 μg/m³, 3.12?±?2.63 μg/m³ and 1.94?±?1.28 μg/m³ for PM_2.5, and 5.61?±?3.79 μg/m³, 1.81?±?1.21 μg/m³ and 1.26?±?0.88 μg/m³ for PM₁, respectively. The major secondary species SO ₄ ^2? , NO ₃ ^? and NH ₄ ⁺ accounted for 5.81%, 1.88% and 1.40% of the total mass of PM_2.5 and 11.10%, 2.68%, and 2.48% of the total mass of PM₁, respectively. The source identification was conducted for the ionic species in PM_2.5 and PM₁ aerosols. The results are discussed by the way of correlations and principal component analysis. Spearman correlation indicated that Cl^? and K⁺ in PM_2.5 and PM₁ can be originated from similar type of sources. Principal component analysis reveals that there are two major sources (anthropogenic and natural such as soil derived particles) for PM_2.5 and PM₁ fractions.     

Asian dust depositions over the Asian region during March 2010 estimated by ADAM2

The Asian Dust Aerosol Model 2 with the MM5 meteorological model has been employed to estimate the dust emission, dust concentration, and wet and dry deposition of dust in the Asian region for the month of March in 2010. It is found that the model simulates quite reasonably the dust (PM₁₀) concentrations both in the dust source region and the downstream region of Korea. The starting and ending times of most dust events and their peak concentration occurrence times are well simulated. The monthly mean maximum surface dust concentration (PM₁₀) is found to be 267???g?m^?3 in the domain of central northern China (CNC). Monthly total maximum dust emission of more than 32?t km^?2 and that of deposition of more than 25.4?t km^?2 (dry deposition of 24?t km^?2 and wet deposition of 1.4?t km^?2) are found to occur in the domain CNC, whereas the monthly mean minimum surface dust concentration (PM₁₀) is found to be 0.2???g?m^?3 in the domain of the Tibetan Plateau, where the monthly total dust emission (4?kg?km^?2) and the monthly total dust deposition (9?kg?km^?2) are found to be minimum. This monthly total dust deposition of 9?kg?km^?2 (dry deposition of 7?kg?km^?2 and wet deposition of 2?kg?km^?2) is as large as 2.25 times of that of emission (4?kg?km^?2), suggesting net dust influx toward the Tibetan Plateau from the surrounding dust source regions. It is also found that the ratio of the total dust deposition to the total dust emission in the source region increases toward the downstream direction from 0.4 in the upstream source region of Taklimakan to 0.80 in the downstream source region of northeastern China. More than 90% of the total dust deposition is found to be contributed by dry deposition due to the lack of precipitation in the dust source region. The monthly mean dust concentration (PM₁₀) is found to decrease with distance away from the dust source region. The monthly mean dust concentration of 62???g?m^?3 over the Yellow Sea (YES) decreases to 4.3???g?m^?3 over the Northwestern Pacific Ocean (NWP). The monthly total dust deposition in the downstream region is also found to decrease away from the source region from 2.33?t km^?2 (dry deposition of 1.36?t km^?2 and wet deposition of 0.97?t km^?2) over the domain YES to 1.45?t km^?2 (dry deposition of 0.16?t km^?2 and wet deposition of 1.30?t km^?2) over the domain NWP. A large amount of the total dust deposition over the seas is contributed by wet deposition (more than 90%), causing a small decreasing rate of the total dust deposition with distance from the source region. The estimated dust deposition could adversely impact the eco-environmental system significantly in the downstream regions of the Asian dust source region, especially over the seas.     

Trace gases and PM2.5-bound metal abundance over a tropical urban environment,South India

Pre and Post-Monsoon levels of ambient SO₂, NO₂, PM_2.5 and the trace metals Fe, Cu, etc. were measured at industrial and residential regions of the Kochi urban area in South India for a period of two years. The mean PM_2.5, SO₂ and NO₂ concentrations across all sites were 38.98?±?1.38 µg/m³, 2.78?±?0.85 µg/m³ and 11.90?±?4.68 µg/m³ respectively, which is lower than many other Indian cities. There was little difference in any on the measured species between the seasons. A few sites exceeded the NAAQS (define acronym and state standard) and most of the sites exceeded WHO (define acronym and state standard) standard for PM_2.5. The average trace metal concentrations (ng/m³) were found to be Fe (32.58)?>?Zn (31.93)?>?Ni (10.13)?>?Cr (5.48)?>?Pb (5.37)?>?Cu (3.24). The maximum concentration of trace metals except Pb were reported in industrial areas. The enrichment factor, of metals relative to crustal material, indicated anthropogenic dominance over natural sources for the trace metal concentration in Kochi’s atmosphere. This work demonstrates the importance of air quality monitoring in this area.