Dui Wu

Determination of Elemental and Organic Carbon in PM2.5 in the Pearl River Delta Region: Inter-Instrument (Sunset vs. DRI Model 2001 Thermal/Optical Carbon Analyzer) and Inter-Protocol Comparisons (IMPROVE vs. ACE-Asia Protocol)

Organic carbon (OC) and elemental carbon (EC) are operationally defined due to the lack of definitive standards. Consequently, their quantification is protocol dependent. IMPROVE and NIOSH are the two widely used thermal/optical protocols for OCEC analysis, differing in temperature programs and in the optical method for charring correction. The IMPROVE protocol is often implemented on a DRI analyzer while the NIOSH protocol is often implemented on a Sunset Laboratory Analyzer. Evaluation of the implementation of the IMPROVE protocol on the Sunset Laboratory analyzer or implementation of the NIOSH or NIOSH-derived protocols on the DRI analyzer has rarely been reported. We analyzed OC and EC in about 100 ambient samples collected in the Pearl River Delta in China by implementing the IMPROVE protocol and a NIOSH-derived (ACE-Asia) protocol on both a DRI Model 2001 analyzer and a Sunset Laboratory analyzer. The total carbon (TC) and EC filter loading as determined by the ACE-Asia protocol on the Sunset analyzer varied from 2.6 to 67.0 and 0.2 to 7.4 μg cm−2, respectively. Inter-instrument comparison indicates that the implementation of the IMPROVE protocol on the Sunset analyzer reports TC, EC, and OC measurements to be in good agreement with those made on the DRI analyzer. EC and OC analyzed using the ACE-Asia protocol are also in good agreements for measurements implemented on the Sunset and DRI analyzers. Inter-protocol comparison indicates consistency in TC determination but discrepancies in OC and EC, with the IMPROVE protocol reporting much higher EC than the ACE-Asia protocol. An analysis of different comparison scenarios reveals that the cause of the EC difference could be quantitatively attributed to temperature protocol (thermal effect) and optical pyrolysis correction method (reflectance vs. transmittance). The variation in EC concentrations was more pronounced in samples that produced more charred OC during thermal analysis. Copyright 2012 American Association for Aerosol Research

A vertical sounding of severe haze process in Guangzhou area

We detected a severe haze process in Guangzhou area with lidar and microwave radiometer, performed an inversion to get boundary layer height by wavelet covariance transform, and analyzed the correlation between meteorological factors of boundary layer and visibility from the perspective of dynamical and thermodynamic structures. Our results indicate that the boundary layer height shows significant daily changes, consistent with ground visibility variation. During the cleaning process, the boundary layer height exceeded 1 km; during severe haze, the height was only 500 m. Temperature gradient of 50–100 m, which was 30 h lag, was remarkably correlated with visibility, with the correlation coefficient of 0.77. High layer visibility (255 m) and low layer stability were significantly anticorrelation, and the maximum anticorrelation coefficient was up to −0.76 in cleaning days and −0.49 in haze days. In the related boundary layer meteorological factors, surface ventilation coefficient was linearly correlated with ground visibility, with the greatest correlation coefficient of 0.88. The correlation coefficients of boundary layer height, ground wind velocity, relative humidity and ground visibility were 0.76, 0.67, and −0.77, respectively. There was a strong correlation between different meteorological factors. The dominant meteorological factor during this haze process was surface ventilation coefficient. In the area without boundary layer height sounding, ground visibility and wind velocity could be used to estimate boundary layer height.

Characterization of Secondary Aerosol and its Extinction Effects on Visibility over the Pearl River Delta Region, China

Aerosol samples collected from July 2007 to March 2008 were used to obtain major aerosol constituents in an urban location in the Pearl River Delta Region (PRD), China. The minimum organic carbon (OC)/elemental carbon (EC) ratio was used to calculate the primary and secondary organic carbon and the extinction effect of the secondary aerosol on visibility was estimated. As indicated in the analysis, the mass of secondary aerosol takes up 50% of the total mass of PM2.5; the OC/EC ratio is larger than 2 and there are significant characteristics of secondary aerosol generation; the levels of secondary OC are comparable with those of sulfate; and there is obvious enrichment of secondary aerosol on more polluted days. In a dry environment, the extinction weight is 59% for the secondary aerosol, while it is as high as 82% if the environment is highly humid (relative humidity [RH] = 95%). The hygroscopic growth of the aerosol can reduce visibility greatly; the secondary aerosol shares much larger quotas on more polluted days. For the Pearl River Delta (PRD), secondary aerosol and carbonaceous aerosol, especially secondary organic carbon (SOC), are a very acute problem; the study of the generating mechanism and sources for secondary aerosol is the key to the effort of controlling visibility in this region. The equation set forth in IMPROVE experiments can only be referenced but is not applicable to evaluate the extinction effect of individual aerosol components on visibility in the PRD region. Implications: The extinction effects on visibility by different constituents are studied in this work using compositional data derived from the measurements, with special efforts on examining the extinction of secondary aerosol and the enrichment and extinction contributions of the constituents with the variation of pollution level and relative humidity, so as to provide a scientific basis for the mitigation of atmospheric aerosol pollution and improving visibility in the PRD of China.

A Study of a Retrieval Method for Temperature and Humidity Profiles from Microwave Radiometer Observations Based on Principal Component Analysis and Stepwise Regression

Abstract This paper discusses the application of principal component analysis and stepwise regression in the retrieval of vertical profiles of temperature and humidity based on the measurements of a 35-channel microwave radiometer. It uses the radiosonde data of 6 yr from Hong Kong, China, and the monochromatic radiative transfer model (MonoRTM) to calculate the brightness temperatures of the 35 channels of the radiometer. The retrieval of the atmospheric profile is then established based on principal component analysis and stepwise regression. The accuracy of the retrieval method is also analyzed. Using an independent sample, the root-mean-square error of the retrieved temperature is less than 1.5 K, on average, with better retrieval results in summer than in winter. Likewise, the root-mean-square error of the retrieved water vapor density reaches a maximum value of 1.4 g m−3 between 0.5 and 2 km, and is less than 1 g m−3 for all other heights. The retrieval method is then applied to the actual measured ...

Nonpolar organic compounds as PM2.5 source tracers: Investigation of their sources and degradation in the Pearl River Delta, China

A group of nonpolar organic compounds (NPOCs) in five compound classes including alkanes, polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes, and 1,3,5-triphenylbenzene (TPB), were quantified in PM2.5 samples collected at four sites in the Pearl River Delta (PRD) region, China over a two-year period from 2011 to 2012. The four sites include industrial (Nanhai), urban (Guangzhou), urban outskirt (Dongguan) and suburban (Nansha) locations. Some NPOCs are uniquely emitted from particular combustion sources, and thereby serving as markers in source apportionment. Based on this multi-year and multi-site NPOC data set, spatial and seasonal variations, correlation analysis and ratio-ratio plots were used to investigate the source information and degradation of NPOC tracers. In summer, NPOCs showed distinct local emission characteristics, with urban sites having much higher concentrations than suburban sites. In winter, regional transport was an important influence on NPOC levels, driving up concentrations at all sampling sites and diminishing an urban-suburban spatial gradient. The lighter NPOCs exhibited more prominent seasonal variations. Such spatiotemporal features suggest their particle-phase abundance is more influenced by temperature, which is a critical factor in controlling the extent of semi-volatile organics partitioned into the aerosol phase. The heavier NPOCs, especially PAHs, showed negligible correlation among the four sites, suggesting more influence from local emissions. Ratio-ratio plots indicate photo-degradation and mixing of various sources for the NPOCs in the PRD. A positive matrix factorization (PMF) analysis of this large NPOC data set suggests that heavier NPOCs are more suitable source indicators than lighter NPOCs. Incorporating particle-phase light NPOC concentrations in PMF produces a separate factor, which primarily contains those light NPOCs and likely is not a source factor. Total NPOC concentrations predicted using Pankow partitioning theory were explored as PMF inputs, however, the PMF solution is not able to fully explain the input total concentrations or to give reasonable source profiles, suggesting the need for reliable gas-phase NPOC data before their use in source apportionment studies. In addition, degradation of NPOCs needs to be considered to avoid misinterpretation of PMF source apportionment results.