J Air Waste Manag Assoc. 2014 Mar;64(3):265-71. doi: 10.1080/10962247.2013.852636.
The U.S. Environmental Protection Agency (EPA), state and local agencies have focused their efforts in assessing secondary fine particulate matter (aerodynamic diameter < or = 2.5 microm; PM2.5) formation in prevention of significant deterioration (PSD) air dispersion modeling. The National Association of Clean Air Agencies (NACAA) developed a method to account for secondary PM2.5 formation by using sulfur dioxide (SO2) and nitrogen oxides (NOx) offset ratios. These ratios are used to estimate the secondary formation of sulfate and nitrate PM2.5. These ratios were first introduced by the EPA for nonattainment areas in the Implementation of the New Source Review (NSR) Program for Particulate Matter Less than 2.5 Micrometers (PM2.5), 73 FR 28321, to offset emission increases of direct PM2.5 emissions with reductions of PM2.5 precursors and vice versa. Some regulatory agencies such as the Minnesota Pollution Control Agency (MPCA) have developed area-specific offset ratios for SO2 and NOx based on Comprehensive Air Quality Model with Extensions (CAMx) evaluations for air dispersion modeling analyses. The current study evaluates the effect on American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) predicted concentrations from the use of EPA and MPCA developed ratios. The study assesses the effect of these ratios on an electric generating utility (EGU), taconite mine, food processing plant, and a pulp and paper mill. The inputs used for these four scenarios are based on common stack parameters and emissions based on available data. The effect of background concentrations also evaluates these scenarios by presenting results based on uniform annual PM2.5 background values. This evaluation study helps assess the viability of the offset ratio method developed by NACAA in estimating primary and secondary PM2.5 concentrations. An alternative Tier 2 approach to combine modeled and monitored concentrations is also presented.
On January 4, 2012, the EPA committed to engage in rulemaking to evaluate updates to the Guideline on Air Quality Models (Appendix W of 40 CFR 51) and, as appropriate, incorporate new analytical techniques or models for secondary PM2.5. As a result, the National Association of Clean Air Agencies (NACAA) developed a screening method involving offset ratios to account for secondary PM2.5 formation. The use of this method is promising to evaluate total (direct and indirect) PM2.5 impacts for permitting purposes. Therefore, the evaluation of this method is important to determine its viability for widespread use.
美国环境保护署（EPA）、州和地方机构一直在努力评估次要细颗粒物（空气动力学直径<或=2.5 微米；PM2.5）在防止显著恶化（PSD）空气扩散模型中的形成。全国清洁空气协会（NACAA）开发了一种方法，通过使用二氧化硫（SO2）和氮氧化物（NOx）抵消比来考虑二次 PM2.5 的形成。这些比率用于估计硫酸盐和硝酸盐 PM2.5 的二次形成。这些比率是由 EPA 首次引入的，用于未达标地区的新源审查（NSR）计划中对小于 2.5 微米的颗粒物（PM2.5）的实施，73 FR 28321，以抵消直接 PM2.5 排放的增加，同时减少 PM2.5 前体的排放，反之亦然。一些监管机构，如明尼苏达州污染控制机构（MPCA），根据综合空气质量模型扩展版（CAMx）对空气扩散模型分析进行评估，为 SO2 和 NOx 制定了特定区域的抵消比率。本研究评估了使用 EPA 和 MPCA 开发的比率对美国气象学会/环境保护局监管模型（AERMOD）预测浓度的影响。该研究评估了这些比率对发电设施（EGU）、铁矿、食品加工厂和纸浆和造纸厂的影响。这四个场景的输入基于常见的烟囱参数和基于现有数据的排放。还通过基于均匀年度 PM2.5 背景值的结果来评估背景浓度对这些场景的影响。这项评估研究有助于评估 NACAA 开发的用于估计一次和二次 PM2.5 浓度的抵消比率方法的可行性。还提出了一种替代的二级方法，将模型化和监测浓度相结合。
2012 年 1 月 4 日，EPA 承诺进行法规制定，以评估空气质量模型指南（40 CFR 51 的附录 W）的更新，并酌情纳入新的二次 PM2.5 分析技术或模型。因此，全国清洁空气协会（NACAA）开发了一种涉及抵消比率的筛选方法，用于考虑二次 PM2.5 的形成。该方法的使用有望用于评估许可目的的总（直接和间接）PM2.5 影响。因此，评估该方法对于确定其广泛使用的可行性非常重要。
