Regression Analyses between Recent Air Quality and Visibility Changes in Megacities at Four Haze Regions in China

The Chinese government has put forward a series of aggressive control measures to tackle environmental problems, such as poor visibility, since the first year of its 11th five-year plan (2006-2010). Recently recorded visibility, air quality and meteorological data in four major megacities (Beijing, Shanghai, Guangzhou and Chengdu) in different haze regions (and climatic zones) of China were analyzed with the aim of evaluating the extent to which the control actions have affected these measures. The ambient concentrations of three major air pollutants (SO2, NO2 and PM10) in these cities all decreased in the years 2005-2009. However, improved visibility was observed only in Beijing and Guangzhou; it remained steady in Shanghai, and showed a decreasing trend in Chengdu. The results highlight the fact that the correlation between air quality and visibility is complex. Optimal empirical regression models were developed, based on measured air quality and meteorological parameter data, to better isolate possible causal correlations between visibility and air quality, as well as meteorological conditions. Our results show that the improvement in visibility in both Beijing and Guangzhou was mainly due to the reduced PM10 concentration. In Guangzhou, improved atmospheric visibility was also helped by a reduction in SO2 concentration in winter. In contrast, lower wind speed, together with possible changes in fine particle concentration and composition, could explain why no improvement in visibility trend was found in Shanghai or Chengdu.</p

Reconstructed Light Extinction Coefficients Using Chemical Compositions of PM2.5 in Winter in Urban Guangzhou, China

The objective of this study was to reconstruct light extinction coefficients (b(ext)) according to chemical composition components of particulate matter up to 2.5 mu m in size (PM2.5). PM2.5 samples were collected at the monitoring station of the South China of institute of Environmental Science (SCIES, Guangzhou, China) during January 2010, and the online absorbing and scattering coefficients were obtained using an aethalometer and a nephelometer. The measured values of light absorption coefficient by particle (b(ap)) and light scattering coefficient by particle (b(sp)) significantly correlated (R-2 &gt; 0.95) with values of b(ap) and b(sp) that were reconstructed using the Interagency Monitoring of Protected Visual Environments (IMPROVE) formula when RH was &lt;70%. The measured b(ext) had a good correlation (R-2 &gt; 0.83) with the calculated bext under ambient RH conditions. The result of source apportionment of bext showed that ammonium sulfate [(NH4)(2)SO4] was the largest contributor (35.0%) to b(ext), followed by ammonium nitrate (NH4NO3, 22.9%), organic matter (16.1%), elemental carbon (11.8%), sea salt (4.7%), and nitrogen dioxide (NO2, 9.6%). To improve visibility in Guangzhou, the effective control of secondary particles like sulfates, nitrates, and ammonia should be given more attention in urban environmental management.</p

Chemical characteristics of PM2.5 during dust storms and air pollution events in Chengdu, China

Daily fine particulate (PM2.5) samples were collected in Chengdu from April 2009 to February 2010 to investigate their chemical profiles during dust storms (DSs) and several types of pollution events, including haze (HDs), biomass burning (BBs), and fireworks displays (FDs). The highest PM2.5 mass concentrations were found during DSs (283.3 mu g/m(3)), followed by FDs (212.7 mu g/m(3)), HDs (187.3 mu g/m(3)), and BBs (130.1 mu g/m(3)). The concentrations of most elements were elevated during DSs and pollution events, except for BBs. Secondary inorganic ions (NO3-, SO42-, and NH4+) were enriched during HDs, while PM2.5 from BBs showed high K+ but low SO42-. FDs caused increases in K+ and enrichment in SO42-. Ca2+ was abundant in DS samples. Ion-balance calculations indicated that PM2.5 from HDs and FDs was more acidic than on normal days, but DS and BB particles were alkaline. The highest organic carbon (OC) concentration was 26.1 mu g/m(3) during FDs, followed by BBs (23.6 mu g/m(3)), HDs (19.6 mu g/m(3)), and DSs (18.8 mu g/m(3)). In contrast, elemental carbon. (EC) concentration was more abundant during HDs (10.6 mu g/m(3)) and FDs (9.5 mu g/m(3)) than during BBs (6.2 mu g/m(3)) and DSs (6.0 mu g/m(3)). The highest OC/EC ratios were obtained during BBs, with the lowest during HDs. SO42-/K+ and TCA/SO42- ratios proved to be effective indicators for differentiating pollution events. Mass balance showed that organic matter, SO42-, and NO3- were the dominant chemical components during pollution events, while soil dust was dominant during DSs.</p

Chemical composition of PM2.5 in an urban environment in Chengdu, China: Importance of springtime dust storms and biomass burning

Daily PM2.5 samples were collected in Chengdu, a megacity in southwest China, for a period of one month in every season during 2009-2010. Mass concentrations of water-soluble inorganic ions, organic carbon (OC), elemental carbon (EC), levoglucosan (LC), water soluble organic carbon (WSOC), and elements were determined to identify the chemical characteristics and potential sources of PM2.5. The data obtained in spring were discussed in detail to explore the impacts of dust storms and biomass burning on the chemical aerosol properties. The daily PM2.5 mass concentrations ranged from 49.2 to 425.0 mu g m(-3) with an annual average of 165.1 +/- 85.1 mu g m(-3). The highest seasonal average of PM2.5 concentrations was observed in the winter (225.5 +/- 73.2 mu g m(-3)) and the lowest in the summer (113.5 +/- 39.3 mu g m(-3)). Dust storm influence was observed only during the spring, while biomass burning activities occurred frequently in late spring and early summer. In the spring season, water-soluble ions, total carbonaceous aerosols, and the sum of the dominant elements (Al, Si, Ca, Ti, Fe, Mn, Zn, Pb, and Cu) accounted for 30.0 +/- 9.3%, 38.6 +/- 11.4%, and 6.2 +/- 5.3%, respectively, of the total PM2.5 mass. Crustal element levels evidently increased during the dust storm episode and LG, OC, WSOC, Cl- and K+ concentrations increased by a factor of 2-7 during biomass burning episodes. Using the Positive Matrix Factorization (PMF) receptor model, four sources for spring aerosols were identified, including secondary sulfate and nitrate, motor vehicle emissions, soil dust, and biomass burning. The four sources were estimated to contribute 24.6%, 18.8%, 23.6% and 33.0%, respectively, to the total PM2.5 mass.</p

Characterization and source apportionment of aerosol light extinction in Chengdu, southwest China

To investigate aerosol properties in the Sichuan Basin of China, field aerosol sampling was carried out in Chengdu, China during four one-month periods, each in a different season in 2011. Aerosol scattering coefficient (b(sp)) at dry (RH&lt;40%) and wet (40% &lt; RH&lt;90%) conditions and aerosol absorption coefficient (b(ap)) were measured. Additionally, daily PM2.5 and PM10 samples were also collected. PM2.5 samples were subject to chemical analysis for various chemical components including major water-soluble ions, organic and elemental carbon (OC and EC), trace elements, as well as anhydrosugar Levoglucosan (LG) and Mannosan (MN). A multiple linear regression analysis was applied to the measured dry b(sp) against (NH4)(2)SO4, NH4NO3, organic mass (OM), fine soil (FS), and coarse mass (CM, PM2.5-10), and to the measured b(ap) against EC in all the four seasons to evaluate the impact of individual chemical components of PM2.5 and CM on aerosol light extinction (b(ext) = b(sp) + b(ap)). Mass scattering efficiency (MSE) and mass absorption efficiency (MAE) of the individual chemical components of PM2.5 were estimated based on seasonal regression equations and were then used for estimating b(ext). The annual b(sp), b(ap) and single scattering albedo (SSA) at dry conditions were 456 +/- 237 Mm(-1), 96 +/- 48 Mm(-1) and 0.82 +/- 0.05, respectively. The annual average b(sp) at ambient conditions estimated through hygroscopic curve of aerosol (f(RH)) was 763 +/- 415 Mm(-1), which was 1.7 times of the dry b(sp). The annual average SSA at ambient conditions also increased to 0.88 +/- 0.04. The estimated dry b(ext) was only 2 +/- 9% higher than the measurements and the estimated ambient bext from individual chemical components was only 1 +/- 10% lower, on an annual basis, than that estimated from using f(RH). Secondary inorganic aerosols, coal combustion, biomass burning, iron and steel industry, Mo-related industry, soil dust, and CM to b(ext) were estimated to account for 41 +/- 19%, 18 +/- 12%, 14 +/- 13%, 13 +/- 11%, 5 +/- 4%, 5 +/- 7% and 4 +/- 3%, respectively, of the estimated ambient b(ext).</p

Characterization of atmospheric organic and elemental carbon of PM2.5 in a typical semi-arid area of northeastern China

In the spring of 2006, daily particulate matter (PM2.5) aerosol samples were collected in Tongyu, a semi-arid area in northeastern China. The concentrations of organic carbon (OC) and elemental carbon (EC) were determined with a thermal/optical carbon analyzer in the filter samples. The average concentrations of OC and EC in PM2.5 were 14.1 &plusmn; 8.7 and 2.0 &plusmn; 1.3 &mu;g/m3, respectively. A good correlation between OC and EC was observed during the spring season, suggesting that they might be derived from similar sources. The correlation between OC and K+ was high (R = 0.74), and the K+/OC ratio, as determined from their linear regression slope, reached 2.57. The good correlation and high K+/OC ratio indicated that biomass-burning was probably one of the major sources of OC in this region. The concentrations of estimated secondary organic carbon (SOC) in PM2.5 in Tongyu ranged from below the detection limit to 26.1 &mu;g/m3 (mean, 5.9 &mu;g/m3). The percentages of SOC in OC and in PM2.5 mass were 42.0% and 2.1%, respectively. The SOC concentrations during dust storm (DS) periods were higher than those during non-dust storm (NDS) ones, suggesting that chemical reaction processes involving gas-particle conversion occurred during the long-distance transport of aerosol particles.</p

Impact of PM2.5 chemical compositions on aerosol light scattering in Guangzhou - the largest megacity in South China

Daily PM2.5 samples were collected in Guangzhou - the largest megacity in South China, for a period of one month in each season during 2009-2010. Mass concentrations of water-soluble inorganic ions, organic carbon (OC) and elemental carbon (EC) in PM2.5 were determined, and aerosol scattering coefficient (b(sp)) was synchronously measured. The daily PM2.5 mass concentrations ranged from 21.0 to 213.6 mu g m(-3) with an annual average of 76.8 +/- 41.5 mu g m(-3). The highest seasonal average PM2.5 was observed in winter (103.3 +/- 50.1 mu g m(-3)) and the lowest in summer (38.6 +/- 15.7 mu g m(-3)). Annual average PM2.5 mass scattering efficiency (MSE) was 3.5 +/- 0.9 m(2) g(-1), with obvious seasonal variations in sequence of autumn (4.5 +/- 0.2 m(2) g(-1)) &gt; winter (3.9 +/- 0.5 m(2) g(-1)) &gt; spring (3.0 +/- 0.4 m(2) g(-1)) &gt; summer (2.3 +/- 0.3 m(2) g(-1)). To determine the relationship between b and the chemical components of PM2.5, b(sp) was reconstructed in each season using the original IMPROVE formula with a modification of including sea salt aerosols. The estimated bsp using this method was 22 +/- 28% smaller on annual average compared to the measurements. Multiple linear regression of measured b(sp) against (NH4)(2)SO4, NH4NO3, OM (Organic Mass), SS (Sea Salt), FS (Fine Soil), and CM (Coarse Mass) were also performed in all the four seasons. The estimated b(sp) from using the regression equation was 4 +/- 12% larger than the measured values. On average, (NH4)(2)SO4, NH4NO3, OM, SS, FS and CM accounted for 50 +/- 11%, 18 +/- 10%, 19 +/- 5%, 5 +/- 4%, 3 +/- 2% and 5 +/- 6%, respectively, of the estimated b(sp).</p

Long-Term Trends in Visibility and at Chengdu, China

Long-term (1973 to 2010) trends in visibility at Chengdu, China were investigated using meteorological data from the U.S. National Climatic Data Center. The visual range exhibited a declining trend before 1982, a slight increase between 1983 and 1995, a sharp decrease between 1996 and 2005, and some improvements after 2006. The trends in visibility were generally consistent with the economic development and implementation of pollution controls in China. Intensive PM2.5 measurements were conducted from 2009 to 2010 to determine the causes of visibility degradation. An analysis based on a modification of the IMPROVE approach indicated that PM2.5 ammonium bisulfate contributed 27.7% to the light extinction coefficient (bext); this was followed by organic mass (21.7%), moisture (20.6%), and ammonium nitrate (16.3%). Contributions from elemental carbon (9.4%) and soil dust (4.3%) were relatively minor. Anthropogenic aerosol components (sulfate, nitrate, and elemental carbon) and moisture at the surface also were important determinants of the aerosol optical depth (AOD) at 550 nm, and the spatial distributions of both bext and AOD were strongly affected by regional topography. A Positive Matrix Factorization receptor model suggested that coal combustion was the largest contributor to PM2.5 mass (42.3%) and the dry-air light-scattering coefficient (47.7%); this was followed by vehicular emissions (23.4% and 20.5%, respectively), industrial emissions (14.9% and 18.8%), biomass burning (12.8% and 11.9%), and fugitive dust (6.6% and 1.1%). Our observations provide a scientific basis for improving visibility in this area.</p

Characteristics and applications of size-segregated biomass burningtracers in China's Pearl River Delta region

Biomass burning activities in China are ubiquitous and the resulting smoke emissions may pose considerable threats to human health and the environment. In the present study, size-segregated biomass burning tracers, including anhydrosugars (levoglucosan (LG) and mannosan (MN)) and nonsea-salt potassium (nss-K&thorn;), were determined at an urban and a suburban site in the Pearl River Delta (PRD) region. The size distributions of biomass burning tracers were generally characterized by a unimodal pattern peaking in the particle size range of 0.44e1.0 mm, except for MN during the wet season, for which a bimodal pattern (one in fine and one in coarse mode) was observed. These observed biomass burning tracers in the PRD region shifted towards larger particle sizes compared to the typical size distributions of fresh biomass smoke particles. Elevated biomass burning tracers were observed during the dry season when biomass burning activities were intensive and meteorological conditions favored the transport of biomass smoke particles from the rural areas in the PRD and neighboring areas to the sampling sites. The fine mode biomass burning tracers significantly correlated with each other, confirming their common sources. Rather high DLG/DMN ratios were observed at both sites, indicating limited influence from softwood combustion. High Dnss-K&thorn;/DLG ratios further suggested that biomass burning aerosols in the PRD were predominately associated with burning of crop residues. Using a simplified receptor-oriented approach with an emission factor of 0.075 (LG/TC) obtained from several chamber studies, average contributions of biomass burning emissions to total carbon in fine particles were estimated to be 23% and 16% at the urban and suburban site, respectively, during the dry season. In contrast, the relative contributions to total carbon were lower than 8% at both sites during the wet season.</p

Saccharides in summer and winter PM2.5 over Xi'an, Northwestern China: Sources, and yearly variations of biomass burning contribution to PM2.5

Saccharides are important constituents in atmospheric aerosols but studies in northwestern China are still very limited. Here, we have measured anhydrosugars (levoglucosan, mannosan and galactosan), primary sugars (glucose, fructose, sucrose and trehalose), and sugar alcohols (arabitol, mannitol, sorbitol and inositol) in ambient PM2.5 samples during summer and winter in Xi&#39;an city, northwestern China. The abundance of total saccharides showed no clear seasonal variation, but apparent distinctions on the levels of the three categories and individual saccharide compounds were found. Primary sugars and particularly sucrose were dominant in summer. In contrast, levoglucosan was the predominant species in winter, contributing 60% of total saccharides. Source apportionment by positive matrix factorization revealed that airborne pollen was a major source of PM2.5 associated-saccharides in summer, accounting for 35% of total saccharides; while biomass burning activities contributed to 60% of the winter saccharides. Furthermore, an increasing trend of biomass/biofuel burning contribution to winter PM2.5 was observed in comparison with previous studies in Xi&#39;an, suggesting a change in emission sources may be underway in northwestern China.</p