Renjian Zhang

Model study on particle size segregation and deposition during Asian dust events in March 2002

[1] A size-segregated aerosol model that includes most of the major physical processes (generation, transport, and dry and wet deposition) is developed. This model is coupled with a Regional Air Quality Model (RAQM) and is applied to simulate Asian dust storms during the 10-day period of 15-24 March 2002. A nonhydrostatic mesoscale model (MM5) is used to provide meteorological fields. Model results are verified by available observational data including surface weather observations and size-segregated particle concentrations. The validation demonstrates a good capability of this model system in capturing most of the key features of dust evolution and reproducing the particle mass size distribution along the transport pathway of soil dust. An apparent feature has been both observed and reproduced by the model, showing a shift of size range with peak mass concentration from coarse mode to finer mode on the pathway from source regions to distant downwind areas. The maximum dust concentration averaged over 10 days is simulated to be 3000 μg m over the southern China-Mongolia border. Total dry deposition of soil dust for 10 days is up to 30 g m -2 in the Gobi desert along the southern China-Mongolia border. Distribution and magnitude of particle deposition are strongly dependent on both concentration and size-segregated dry deposition velocity and scavenging rate. While dry deposition dominates the removal of dust particles in or in the vicinity of source regions, the influence of wet deposition increases along the transport pathway of soil dust, with high removal efficiency for coarser particles (>2 μm) and very low efficiency for particles in the accumulation mode. Of the total dust emission (43.2 megatons), about 71% is redeposited onto the underlying surface by the dry deposition process, 6% is removed by the wet deposition process, and the remaining 23% is suspended in the atmosphere or subject to long-range transport.

Seasonal Variations and Evidence for the Effectiveness of Pollution Controls on Water-Soluble Inorganic Species in Total Suspended Particulates and Fine Particulate Matter from Xi'an, China

Abstract Total suspended particulate (TSP) and particulate matter less than 2.5 μm in aerodynamic diameter (PM2.5) sam ples were collected over Xi’an for a 1-yr period to characterize the seasonal variations of water-soluble inorganic ions and to evaluate the effectiveness of the pollution policies and controls during the past 10 yr. Mass concentrations of five cations (sodium [Na+], potassium [K+], ammonium [NH4 +]], calcium [Ca2+], and magnesium [Mg2+) and four anions (fluoride [F−], chloride [Cl−], nitrate [NO3 −], and sulfate [SO4 2−]) were determined by ion chromatography. The yearly arithmetic-mean mass concentrations of the total measured water-soluble ions in TSP and PM2.5 were 83.9 ± 58.4 and 45 ± 34.3 μg∙m-3. The most abundant ions in TSP were SO4 2−, NO3 −, Ca2+, and NH4 +; whereas in PM2.5 the dominant ions were SO4 2−, NH4 +, and NO3 −. Most of the ions were more concentrated in the PM2.5 than in TSP, but two exceptions were Ca2+ and Mg2+. Comparisons of the molar ratios of Mg2+/Ca2+ in TSP indicated that fugitive dust was the main source for these two ions, and the influence of soil dust from outside of the city was most evident during dust storms. The mass concentrations of SO4 2−, NO3 −, NH4 +, and K+ in TSP were highest in winter and lowest in spring, but Ca2+ was much higher in spring than other seasons because of suspended mineral dust. In PM2.5, NO3 − and K+ also showed winter maxima, but SO4 2− and NH4 + were highest in summer. Calculations of ion equivalents showed that TSP samples were more alkaline than PM2.5, the latter being weakly acidic in winter and autumn. High sulfur and nitrogen oxidation ratios occurred in summer and autumn, and there was evidence for the formation of ammonium bisulfate in TSP, ammonium sulfate in PM2.5, and ammonium nitrate in both fractions. Comparisons with the results of prior studies indicate that pollution controls in Xi’an have reduced the levels of air pollution over the past 10 yr. The SO4 2− concentration during the heating season in 2006 was only about one-eighth of that in 1996, and NH4 + decreased to one-ninth of that in 1996. Seasonal variations in the NO3 −/SO4 2− ratio are different than the patterns observed 10 yr ago, suggesting that emission sources have changed, with those from motor vehicles becoming increasingly important.

Carbonaceous aerosols in PM10 and pollution gases in winter in Beijing

An intensive observation of organic carbon (OC) and elemental carbon (EC) in PM10 and gaseous materials (SO2, CO, and O3) was conducted continuously to assess the characteristics of wintertime carbonaceous aerosols in an urban area of Beijing, China. Results showed that the averaged total carbon (TC) and PM10 concentrations in observation period are 30.2 +/- 120.4 and 172.6 +/- 198.3 microg/m3, respectively. Average OC concentration in nighttime (24.9 +/- 19.6 microg/m3) was 40% higher than that in daytime (17.7 +/- 10.9 microg/m3). Average EC concentrations in daytime (8.8 +/- 15.2 microg/m3) was close to that in nighttime (8.9 +/- 15.1 microg/m3). The OC/EC ratios in nighttime ranging from 2.4 to 2.7 are higher than that in daytime ranging from 1.9 to 2.0. The concentrations of OC, EC, PM10 were low with strong winds and high with weak winds. The OC and EC were well correlated with PM10, CO and SO2, which implies they have similar sources. OC and EC were not well correlated with 03. By considering variation of OC/EC ratios in daytime and night time, correlations between OC and O3, and meteorological condition, we speculated that OC and EC in Beijing PM10 were emitted as the primary particulate form. Emission of motor vehicle with low OC/EC ratio and coal combustion sources with high OC/EC ratio are probably the dominant sources for carbonaceous aerosols in Beijing in winter. A simple ratio method was used to estimate the relative contribution of sources to carbonaceous aerosols in Beijing PM10. Motor vehicle source accounts for 80% and 68%, while coal combustion accounts for 20% and 32% in daytime and nighttime, respectively in Beijing. Averagely, the motor vehicle and coal combustion accounted for 74% and 26%, respectively, for carbonaceous aerosols during the observation period. It points to the motor vehicle is dominant emission for carbonaceous aerosols in Beijing PM10 in winter period, which should be paid attention to control high level of PM10 in Beijing effectively.

Visual range trends in the Yangtze River Delta Region of China, 1981-2005.

ABSTRACT Visual range (VR) data from 1981 to 2005 were examined for 20 meteorological monitoring sites in the Yangtze River Delta Region of China. Cumulative percentile analysis was used to construct VR trend. The 25-yr average domain-average 50% VR was approximately 21.9 ±1.9 km. Domain-average 50% VR decreased from 1981 to 2005 with a trend of −2.41 km/decade. The worst 20% and 50% and best 20% VR and variation rates for the 20 sites were analyzed. The 50% VR of the town, county-level city, and prefecture-level city sites were 24.1, 21.5, and 19.4 km, respectively. The best 20% VR decreased fastest with a rate of −3.5 km/decade. Regional median VR decreased from the coastal sites to the inland sites. Ridit analysis and cumulative percentile were adopted to study the VR variation properties between economically developed areas (e.g., Nanjing and Hangzhou) and remote areas (e.g., Lvsi). The two analyses show that VR decreased in Nanjing and Hangzhou but remained constant in Lvsi from 1981 to 2005. IMPLICATIONS Decreasing VR corresponds to greater industrialization and particulate concentrations. Moving pollution sources from the coastal to inland locations only moves the decreasing visibility elsewhere. This work offered a good opportunity to comprehend the VR variation in the most developed region of China over the last 2 decades.

Inorganic chemical composition and source signature of PM2.5 in Beijing during ACE-Asia period

Aerosol samples for PM2.5 were collected in Beijing for 38 consecutive days from March to April 2001 using an IMPROVE Sampler. Concentrations of w0 elements in PM2.5 were determined using a PIXE method. Results show that he average mineral dust concentration of PM2.5 was 14.6 μg/m3 during the observation period. On the sanddust event days of March 21 and April 10, dust PM2.5 mass concentrations were 62.4 and 54.1 μg/m3, respectively. These demonstrate that fine particle pollution by dust event in Beijing was very severe. The enrichment factors of S and Cu reached minimums on the dusty days and were high on the non-dusty days. It is considered that enrichment factors of elements in PM2.5, which are associated with human activities, can probably provide an effective method to distinguish local sources from external sources of dust. Factor analysis on the chemical composition in PM2.5 shows that sources of crustal matters, anthropogenic emission, and oil combustion contributed to PM2.5 levels in air in the springtime of 2001 in Beijing.

Impacts of biogenic emissions of VOC and NOx on tropospheric ozone during summertime in eastern China.

This study is intended to understand and quantify the impacts of biogenic emissions of volatile organic compounds (VOC) and nitrogen oxides (NO(x)) on the formation of tropospheric ozone during summertime in eastern China. The model system consists of the non-hydrostatic mesoscale meteorological model (MM5) and a tropospheric chemical and transport model (TCTM) with the updated carbon-bond chemical reaction mechanism (CBM-IV). The spatial resolution of the system domain is 30 km x 30 km. The impacts of biogenic emissions are investigated by performing simulations (36 h) with and without biogenic emissions, while anthropogenic emissions are constant. The results indicate that biogenic emissions have remarkable impacts on surface ozone in eastern China. In big cities and their surrounding areas, surface ozone formation tends to be VOC-limited. The increase in ozone concentration by biogenic VOC is generally 5 ppbv or less, but could be more than 10 ppbv or even 30 ppbv in some local places. The impacts of biogenic NO(x) are different or even contrary in different regions, depending on the relative availability of NO(x) and VOC. The surface ozone concentrations reduced or increased by the biogenic NO(x) could be as much as 10 ppbv or 20 ppbv, respectively. The impacts of biogenic emissions on ozone aloft are generally restricted to the boundary layer and generally more obvious during the daytime than during the nighttime. This study is useful for understanding the role of biogenic emissions and for planning strategies for surface ozone abatement in eastern China. Due to limitations of the emission inventories used and the highly non-linear nature of zone formation, however, some uncertainties remain in the results.

Source apportionment of PM2.5 at urban and suburban areas of the Pearl River Delta region, south China - With emphasis on ship emissions

Daily PM2.5 samples were collected at an urban site in Guangzhou in 2014 and at a suburban site in Zhuhai in 2014-2015. Samples were subject to chemical analysis for various chemical components including organic carbon (OC), element carbon (EC), major water-soluble inorganic ions, and trace elements. The annual average PM2.5 mass concentration was 48±22μgm-3and 45±25μgm-3 in Guangzhou and Zhuhai, respectively, with the highest seasonal average concentration in winter and the lowest in summer at both sites. Regional transport of pollutants accompanied with different air mass origins arriving at the two sites and pollution sources in between the two cities caused larger seasonal variations in Zhuhai (>a factor of 3.5) than in Guangzhou (<a factor of 2.0). Positive matrix factorization (PMF) analysis identified six and five major source factors for PM2.5 in Guangzhou and Zhuhai, respectively. Ship emissions, a source factor previously ignored in making emission control policies in the Pearl River Delta region of south China, were among the top contributors to PM2.5 at both sites, accounting for >17% of PM2.5 mass concentrations.

Seasonal characterization of dust days, mass concentration and dry deposition of atmospheric aerosols over qingdao, china

The seasonal characterization of dust days, mass concentration and dry deposition of atmospheric aerosols were investigated using the historical data of dust days observed over Qingdao during the period from 1961 to 2001 and ground-based aerosol sampling data collected in the period from May 2001 to November 2002. In Qingdao most of the dust days occurred in spring and in winter and no dust days existed in summer. The seasonal variation of the uplifting dust day over Qingdao was in phase with that analyzed over North China. The mean mass concentration of the total suspended particles (TSP) in spring, summer, autumn and winter was respectively 300, 110, 113 and 185 μg·m−3. The values and phase of the seasonal oscillation for fine particles were very similar to those for coarse particles except for the month March, during which the concentration of the coarse particles was about 4 times as high as that of the fine particles. Comparison between seasonal variation of mass concentration of aerosols and dust days indicated that high frequency of uplifting dust day was accompanied by high TSP mass concentration. The TSP mass concentration measured by the low-volume instrument was about 30% lower than that measured by high-volume instrument, though the two data sets are highly correlated (correlation coefficient=0.89). The dry deposition flux during the observation period from May 2001 to November 2002 ranged from 0.06 to 0.2 g·m−2·d−1 with a mean value of 0.13 g·m−2·d−1, which was about 1/3 as that over Beijing.

Control of PM2.5 in Guangzhou during the 16th Asian Games period: Implication for hazy weather prevention

To evaluate the effectiveness of the integrated control measures for reducing PM2.5 (aerosol particles with an aerodynamic diameter of less than 2.5 μm) and hazy weather, day- and night-time PM2.5 samples were collected at an urban site in Guangzhou during the 16th Asian Games period in November 2010. PM2.5 samples were subject to chemical analysis for major water-soluble ions, organic carbon (OC), element carbon (EC), and biomass burning tracers-anhydrosugar levoglucosan (LG). In addition, aerosol scattering coefficient (bsp) at dry condition and aerosol absorption coefficient (bap) and visibility at ambient condition were measured. The seven major control measures were effective for reducing PM2.5 mass concentration and improving visibility during the Asian Games period. All monitored air pollutants except PM2.5 satisfied the National Ambient Air Quality Standards (NAAQS). However, daily PM2.5 concentrations still exceeded the NAAQS on 47% of the days and hazy weather also occurred on 80% of the days during this period. One factor causing the high frequency of hazy weather occurrence was the increased relative humidity during the Asian Games period. To avoid hazy weather occurrence, new PM2.5 standard was recommended based on visibility calculations using three available aerosol hygroscopic curves previously obtained for this city. The recommended PM2.5 standard was 63 μgm(-3) under dry condition and lower than 42 μg m(-3) under humid condition (RH ≥ 70%). These recommended value s were much stricter than the NAAQS value of 75 μg m(-3). To reach the new standard, more rigorous control measures for coal industries should be established in the Pearl River Delta (PRD) region.

Black carbon in a continental semi‐arid area of Northeast China and its possible sources of fire emission

[1] Surface continuous measurements on black carbon (BC) were performed at Tongyu (44.42°N, 122.87°E) from March to December 2008. Tongyu is an international reference site of semi-arid climate and environment researches, located in a continental semi-arid area of northeastern China. Mass concentrations and potential contributing sources of BC are discussed for the sampling site. Hourly BC concentrations ranged from 77.61 ng m-3 to 59.55 μg m -3 with an average of 2.52 μg m -3 , showing a clear seasonal pattern with high values in spring, fall, and winter and low values in summer. Events of high BC concentrations occurred frequently in spring as a result of long-range transport of polluted air masses from the north, northwest, and south in the atmosphere over the Asian continent. The Yangtse River Delta (YRD) and China Anhui Province, the North China Plain (NCP), Northeast China, the Mongolian boundary near China and Russia, Middle Asia, and some areas of Russian Far East were major potential contribution sources for the observed pollutants. The region between Jiangsu Province and Anhui Province of China and the boundary regions between China and Russian Primorskiy and Khabarovskiy were possible source areas of fire emissions having great contributions to high BC levels at Tongyu. The region between Jiangsu Province and Anhui Province of China was the most important anthropogenic fire source of agricultural residue burning outflows.