Consistency of long-term elemental carbon trends from thermal and optical measurements in the IMPROVE network

Decreasing trends of elemental carbon (EC) have been reported at US Interagency Monitoring of PROtected Visual Environments (IMPROVE) network from 1990 to 2004, consistent with the phase-in of cleaner engines, residential biomass burning technologies, and prescribed burning practices. EC trends for the past decade are examined due to an upgrade of IMPROVE carbon instruments and the thermal/optical analysis protocol since 2005. Filter reflectance (tau(R)) values measured as part of the carbon analysis were retrieved from archived data and compared with EC for 65 sites with more complete records within 2000-2009. EC-tau(R) relationships suggest minor changes of EC quantified by the original and upgraded instruments for most IMPROVE samples. EC and tau(R) show universal decreasing trends across the US. The EC and tau(R) trends are correlated, with national average downward rates (relative to the 2000-2004 baseline medians) of 4.5% yr(-1) for EC and 4.1% yr(-1) for tau(R). The consistency between independent EC and tau(R) measurements adds to the weight of evidence that EC reductions are real rather than an artifact of changes to the measurement process.</p

Wintertime particulate pollution episodes in an urban valley of the Western US: a case study

This study investigates the causes of elevated PM2.5 episodes and potential exceedences of the US National Ambient Air Quality Standards (NAAQS) in Truckee Meadows, Nevada, an urban valley of the Western US, during winter 2009/2010, an unusually cold and snowy winter. Continuous PM2.5 mass and time-integrated chemical speciation data were acquired from a central valley monitoring site, along with meteorological measurements from nearby sites. All nine days with PM2.5 &gt; 35 mu g m(-3) showed 24-h average temperature inversion of 1.5-4.5 degrees C and snow cover of 8-18 cm. Stagnant atmospheric conditions limited wind ventilation while highly reflective snow cover reduced daytime surface heating creating persistent inversion. Elevated ammonium nitrate (NH4NO3) and water associated with it are found to be main reasons for the PM2.5 exceedances. An effective-variance chemical mass balance (EV-CMB) receptor model using locally-derived geological profiles and inorganic/organic markers confirmed secondary NH4NO3 (27-37 %), residential wood combustion (RWC; 11-51 %), and diesel engine exhaust (7-22 %) as the dominant PM2.5 contributors. Paved road dust and de-icing materials were minor, but detectable contributors. RWC is a more important source than diesel for organic carbon (OC), but vice versa for elemental carbon (EC). A majority of secondary NH4NO3 is also attributed to RWC and diesel engines (including snow removal equipment) through oxides of nitrogen (NOx) emissions from these sources. Findings from this study may apply to similar situations experienced by other urban valleys.</p

Standards and Traceability for Air Quality Measurements: Flow Rates and Gaseous Pollutants

Accurate and precise flow rate and gas concentration measurement standards are needed for comparable air quality measurements. Transfer standards are most often used for calibration, performance testing, and auditing of field monitors. These must be traceable to primary standards that are in turn derived from fundamental units of length, mass, temperature, and time. Flow rates and volumes are measured by devices based on positive displacement, pressure differences, and temperature increases or decreases. Stable gas concentrations are prepared in non-reactive pressurized containers by gravimetric and dilution methods. Reactive gases are generated from photochemistry and permeation devices. These standards are used to determine the accuracy, precision, and validity of air quality measurements, and these attributes should be reported with the measurement values.</p

Impact of biomass burning on haze pollution in the Yangtze River delta, China: a case study in summer 2011

Open biomass burning is an important source of air pollution in China and globally. Joint observations of air pollution were conducted in five cities (Shanghai, Hangzhou, Ningbo, Suzhou and Nanjing) of the Yangtze River delta, and a heavy haze episode with visibility 2.9-9.8 km was observed from 28 May to 6 June 2011. The contribution of biomass burning was quantified using both ambient monitoring data and the WRF/CMAQ (Weather Research and Forecasting (WRF) and Community Multiscale Air Quality (CMAQ)) model simulation. It was found that the average and maximum daily PM2.5 concentrations during the episode were 82 and 144 mu gm(-3), respectively. Weather pattern analysis indicated that stagnation enhanced the accumulation of air pollutants, while the following precipitation event scavenged the pollution. Mixing depth during the stagnant period was 240-399 m. Estimation based on observation data and CMAQ model simulation indicated that biomass open burning contributed 37% of PM2.5, 70% of organic carbon and 61% of elemental carbon. Satellite-detected fire spots, back-trajectory analysis and air quality model simulation were integrated to identify the locations where the biomass was burned and the pollutants transport. The results suggested that the impact of biomass open burning is regional, due to the substantial inter-province transport of air pollutants. PM2.5 exposure level could be reduced 47% for the YRD region if complete biomass burning is forbidden and significant health benefit is expected. These findings could improve the understanding of heavy haze pollution, and suggest the need to ban open biomass burning during post-harvest seasons.</p

Indoor/Outdoor Relationships for Organic and Elemental Carbon in PM2.5 at Residential Homes in Guangzhou, China

Nine residential areas were selected in this study (three homes in urban areas, three homes near roadsides, and three homes in industrial zones) to evaluate the indoor and outdoor relationship and carbonaceous species characteristics of PM2.5 in Guangzhou, China, during summer and winter 2004. Daily (24 h) average PM2.5 samples were collected on pre-fired quartz-fiber filters with low-volume samplers and analyzed by the thermal optical reflectance (TOR) method following the Interagency Monitoring of PROtected Visual Environments (IMPROVE) protocol. The average indoor and outdoor concentrations of PM2.5 were 88.8 mu g/m(3) and 99.1 mu g/m(3), respectively. The average indoor OC and EC concentrations were 21.7 mu g/m(3), and 7.6 mu g/m(3), respectively, accounting for an average of 25.5% and 8.9% indoor PM2.5 mass, respectively. The average indoor and outdoor OC/EC ratios were 3.4 and 3.0, respectively. The average I/O ratios of PM2.5, OC and EC were 0.91, 1.02 and 0.96, respe! ctively. Poor indoor-outdoor correlations were observed for OC in the summer (R-2 = 0.18) and winter (R-2 = 0.33), while strong correlations (R-2 &gt; 0.8) were observed for EC during summer and winter. OC and EC were moderately correlated (R-2 = 0.4) during summer, while OC and EC correlated well during winter, with a correlation coefficient of 0.64 indoors and 0.75 outdoors. Similar distributions of eight carbon fractions in indoor and outdoor TC pointed to the contributions of motor vehicle exhaust and coal-combustion sources. A simple estimation indicates that about ninety percent of carbonaceous particles in indoor air result from penetration of outdoor pollutants, and indoor sources contribute only ten percent of the indoor carbonaceous particles.</p

Quality assurance and quality control for thermal/optical analysis of aerosol samples for organic and elemental carbon

Accurate, precise, and valid organic and elemental carbon (OC and EC, respectively) measurements require more effort than the routine analysis of ambient aerosol and source samples. This paper documents the quality assurance (QA) and quality control (QC) procedures that should be implemented to ensure consistency of OC and EC measurements. Prior to field sampling, the appropriate filter substrate must be selected and tested for sampling effectiveness. Unexposed filters are pre-fired to remove contaminants and acceptance tested. After sampling, filters must be stored in the laboratory in clean, labeled containers under refrigeration (&lt; 4 A degrees C) to minimize loss of semi-volatile OC. QA activities include participation in laboratory accreditation programs, external system audits, and interlaboratory comparisons. For thermal/optical carbon analyses, periodic QC tests include calibration of the flame ionization detector with different types of carbon standards, thermogram inspection, replicate analyses, quantification of trace oxygen concentrations (&lt; 100 ppmv) in the helium atmosphere, and calibration of the sample temperature sensor. These established QA/QC procedures are applicable to aerosol sampling and analysis for carbon and other chemical components.</p

Characteristics of fine particulate non-polar organic compounds in Guangzhou during the 16th Asian Games: Effectiveness of air pollution controls

The concentrations of organic compounds, including n-alkanes and polycyclic aromatic hydrocarbons (PAHs), in fine particles (PM2.5) were measured in an urban area of Guangzhou before, during, and after the 16th Asian Games (9-30 November 2010). Higher average concentrations of n-alkanes and PAHs occurred in the nighttime, presumably due to a restriction on motor vehicle operation during the day and the accumulation of pollutants due to temperature inversions at night. The carbon preference index, contributions of wax n-alkanes, and PAHs diagnostic ratios indicated that the main sources of n-alkanes and PAHs were anthropogenic, especially motor vehicle emissions. The CMAQ model was used to estimate the percentages of biogenic organic aerosol in the total organic aerosol, then the ratios of source marker PAHs to biogenic organic carbon were used to evaluate the air pollution control policies effectiveness during the Asian Games.</p

Lead concentrations in fine particulate matter after the phasing out of leaded gasoline in Xi’an, China

Daily concentrations of lead (Pb) were determined for PM2.5 samples collected from an urban location in Xi&rsquo;an, China from 2007 to 2009 to assess the effects of the phasing out of leaded gasoline in 2000. The Pb concentrations (annual average: 0.306 &mu;g m&minus;3, range: below detection limit to 2.631 &mu;g m&minus;3) have declined after the phasing out of leaded gasoline, but the concentrations were still higher than those reported in many other cities. Seasonal variations of Pb were significant, with high concentrations in winter, presumably due to the burning of coal, and low concentrations in summer, due to a deep mixed layer and scavenging of aerosols by precipitation. Correlation analyses and enrichment factor calculations both indicated that anthropogenic sources had a large influence on atmospheric Pb. The lead isotope ratios were low in winter (the average 207Pb/206Pb ratio was 0.843 &plusmn; 0.032; 208Pb/206Pb was 1.908 &plusmn; 0.058) and high in summer (207Pb/206Pb was 0.860 &plusmn; 0.032; 208Pb/206Pb was 2.039 &plusmn; 0.057), suggesting that coal combustion was the major Pb source in winter and vehicular emission was the major Pb source in summer. Positive Matrix Factorization receptor model indicated that there were five major sources for Pb in PM2.5. Coal combustion was the major contributor, accounting for 39.0% PM2.5 mass, followed by vehicular emissions (30.4%). Other contributors included 17.8% from industrial emissions, 11.6% from biomass burning, and 1.2% from fugitive dust.</p