Seasonal and Regional Variations of Primary and Secondary Organic Aerosols over the Continental United States: Semi-Empirical Estimates and Model Evaluation
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- 作者：Shaocai Yu ; Prakash V. Bhave ; Robin L. Dennis ; Rohit Mathur
- 刊名：Environmental Science & Technology
- 出版年：2007
- 出版时间：July 1, 2007
- 年：2007
- 卷：41
- 期：13
- 页码：4690 - 4697
- 全文大小：611K
- 年卷期：v.41,no.13(July 1, 2007)
- ISSN：1520-5851
文摘
Seasonal and regional variations of primary (OCpri) andsecondary (OCsec) organic carbon aerosols across thecontinental United States for the year 2001 were examinedby a semi-empirical technique using observed OC andelemental carbon (EC) data from 142 routine monitoringsites in mostly rural locations across the country, coupledwith the primary OC/EC ratios, obtained from a chemicaltransport model (i.e., Community Multiscale Air Quality (CMAQ)model). This application yields the first non-mechanisticestimates of the spatial and temporal variations in OCpri andOCsec over an entire year on a continental scale. Thereis significant seasonal and regional variability in the relativecontributions of OCpri and OCsec to OC. Over the continentalUnited States, the median OCsec concentrations are0.13, 0.36, 0.63, 0.44, and 0.42 
g C m-3 in winter (DJF),spring (MAM), summer (JJA), fall (SON), and annual,respectively, making 21, 44, 51, 42, and 43% contributionsto OC, respectively. OCpri exceeds OCsec in all seasonsexcept summer. Regional analysis shows that the southeasternregion has the highest concentration of OCpri (annualmedian = 1.35 g C m-3), whereas the central region hasthe highest concentration of OCsec (annual median =0.76 g C m-3). The mechanistic OCsec estimates from theCMAQ model were compared against the independentlyderived semi-empirical OCsec estimates. The results indicatethat the mechanistic model reproduced the monthlymedians of the semi-empirical OCsec estimates well overthe northeast, southeast, midwest, and central regions in allmonths except the summer months (June, July, andAugust), during which the modeled regional monthlymedians were consistently lower than the semi-empiricalestimates. This indicates that the CMAQ model is missingOCsec formation pathways that are important in the summer.
g C m-3 in winter (DJF),spring (MAM), summer (JJA), fall (SON), and annual,respectively, making 21, 44, 51, 42, and 43% contributionsto OC, respectively. OCpri exceeds OCsec in all seasonsexcept summer. Regional analysis shows that the southeasternregion has the highest concentration of OCpri (annualmedian = 1.35 g C m-3), whereas the central region hasthe highest concentration of OCsec (annual median =0.76 g C m-3). The mechanistic OCsec estimates from theCMAQ model were compared against the independentlyderived semi-empirical OCsec estimates. The results indicatethat the mechanistic model reproduced the monthlymedians of the semi-empirical OCsec estimates well overthe northeast, southeast, midwest, and central regions in allmonths except the summer months (June, July, andAugust), during which the modeled regional monthlymedians were consistently lower than the semi-empiricalestimates. This indicates that the CMAQ model is missingOCsec formation pathways that are important in the summer.