Variations of Particle Size Distribution, Black Carbon, and Brown Carbon during a Severe Winter Pollution Event over Xi'an, China

Real-time particulate matter (PM) size distributions, 4-hour time resolution, PM2.5, carbonaceous materials, and their optical properties were measured during a severe pollution event in Xi'an, China High PM2.5 /PM10 ratios were observed on both pollution (0.83) and non-pollution (0.73) days, emphasizing the abundance of fine particles during sampling days. The particle number (PN) first peaked with a wide size range (30-100 nm) before morning rush hours (approximately 01:00-05:00) on pollution and non-pollution days, demonstrating that PN was governed by the accumulation of freshly emitted diesel particles and characterized by distinct aerosol condensation growth. By contrast, the second peak time and size range differed between pollution and non-pollution days because of different formation mechanisms The light-absorbing coefficients of both black carbon (BC, b(abs-880nm,BC)) and brown carbon (BrC, b(abs-370nm, BrC)) were high on pollution days and decreased to approximately half of those values on non-pollution days, indicating that the degree of light absorption is reduced by rain. The diurnal variation in b(abs-880nm, BC) pollution peaked with traffic on January 1 and 2. By contrast, it remained in relatively stable and high ranges (120-160 Mm(-1)) in the second period (January 3-5) without traffic peaks, illustrating that the dominant sources changed even during the same pollution period. High values of both b(abs-370nm, BrC) and b(abs-880nm,) (BC )coincided in the afternoon and evening due to emissions from primary sources, and abundant aqueous secondary organic carbon, respectively. A highly variable mass absorption coefficient of BrC also indicated the variety of fuel combustion sources of primary BrC in Xi'an

Optical characteristics and source apportionment of brown carbon in winterPM2.5 over Yulin in Northern China

In this study, daily PM2.5 samples were collected at an urban site in Yulin of Northern China during a winter season. Eight carbon fractions, 13 kinds of polycyclic aromatic hydrocarbons (PAHs), and nine water-soluble ions in PM2.5 were measured. The light-absorption characteristics of brown carbon (BrC) both in water and in methanol extracts were evaluated and quantified. The total quantified PAHs exhibited high concentrations (228.4 ± 52.6 ng m−3), contributing 0.2% of the PM2.5 mass. High indeno[1,2,3-cd]pyrene/(indeno[1,2,3-cd]pyrene + benzo[ghi]-perylene) ratio but low NO3−/SO42− ratio revealed the important contribution of coal combustion to PM2.5. The absorption coefficient (babs) for methanol extracts measured at 365 nm averaged 27.5 ± 12.0 Mm−1. Light absorption by methanol extracts exhibited strong wavelength dependence, with an average absorption Ångström exponent of 5.2 in the 330–400 nm range. The mass absorption cross section (for methanol extracts averaged 1.4 ± 0.4 m2 g−1 by normalizing babs measured at 365 nm to organic carbon mass. A relatively strong positive relationship between babs, methanol and benzo[a]pyrene as well as with six carbon fractions indicated the important contribution of coal burning to BrC. Source apportionment based on the positive matrix factorization receptor model and multiple linear regression showed that residential coal combustion accounted for 37.4% of babs365,methanol. The estimated relative radiative forcing by methanol-soluble organic carbon relative to elemental carbon was 36.9% at 300–400 nm

Characteristics of surface O-3 over Qinghai Lake area in Northeast Tibetan Plateau, China

Surface 03 was monitored continuously during Aug. 12, 2010 to Jul. 21, 2011 at a high elevation site (3200 m above sea level) in Qinghai Lake area (36 58&#39;37 &#39;&#39; N, 99 degrees 53&#39;56 &#39;&#39; E) in Northeast Tibetan Plateau, China. Daily average O-3 ranged from 21.8 ppbv to 653 ppbv with an annual average of 41.0 ppbv. Seasonal average of O-3 followed a decreasing order of summer &gt; autumn &gt; spring &gt; winter. Diurnal variations of O-3 showed low concentrations during daytime and high concentrations during late night and early morning. An intensive campaign was also conducted during Aug. 13-31, 2010 to investigate correlations between meteorological or chemical conditions and O-3. It was found that O-3 was poorly correlated with solar radiation due to the insufficient NOx in the ambient air, thus limiting O-3 formation under strong solar radiation. In contrast, high O-3 levels always coincided with strong winds, suggesting that stratospheric O-3 and long range transport might be the main sources of O-3 in this rural area. Back-trajectory analysis supported this hypothesis and further indicated the transport of air masses from northwest, northeast and southeast directions.</p