VOCs与非甲烷总烃

VOCs与非甲烷总烃

1、定义

VOC是挥发性有机化合物(volatile organic compounds)的英文缩写。其定义有好几种：

世界卫生组织(WHO,1989)对总挥发性有机化合物（TVOC）的定义为，熔点低于室温而沸点在50～260℃之间的挥发性有机化合物的总称。

国标《室内装饰装修材料内墙涂料中有害物质限量》中VOC含量的定义是：“涂料中总挥发物含量扣减水分含量，即为涂料中挥发性有机化合物含量。”

美国ASTM D3960-98标准将VOC定义为任何能参加大气光化学反应的有机化合物。

美国联邦环保署(EPA)的定义：挥发性有机化合物是除CO、CO2、H2CO3、金属碳化物、金属碳酸盐和碳酸铵外，任何参加大气光化学反应的碳化合物。

炼油与石油化学工业大气污染物排放标准DB11/ 447-2007定义为在20℃条件下蒸气压大于或等于0.01 kPa，或者特定适用条件下具有相应挥发性的全部有机化合物的统称

室内空气质量标准GB/T18883-2002总挥发性有机化合物定义为：利用T enax GC或Tenax TA采样，非极性色谱柱（极性指数小于<=3）进行分析，保留时间在正己烷和正十六烷之间的挥发性有机化合物。

VOC的定义分为二类，一类是普通意义上的VOC定义，只说明什么是挥发性有机物，或者是在什么条件下是挥发性有机物；另一类是环保意义上的定义，也就是说，是活泼的那一类挥发性有机物，即会产生危害的那一类挥发性有机物。

我们通常参考世界卫生组织中的定义。

非甲烷总烃（NMHC）指除甲烷以外的碳氢化合物C其中主要是（C2～C8）的总称。（也有资料指C2-C12），在规定的条件下所测得的NMHC是于气相色谱氢火焰离子化检测器有明显响应的除甲烷外碳氢化合物总量，以碳计。

非甲烷总烃主要包括烷烃、烯烃、芳香烃和含氧烃等组分。烃类物质在通常条件下，除甲烷基化为气体外多以液态或固态存在，并依据其分子师大小结构形式的差别具有不同的蒸气压，因而作为大气污染物质非甲烷总烃，实际上是指具有C2-C12的烃类物质。

2、分析方法：

VOC：

2．1空气和废气监测分析方法(四)中《固体吸附热脱附气相色谱-质谱法》或《用采样罐采样气相色谱-质谱法》

2．2 ISO 16017-1 Indoor, ambient and workplace air -- Sampling and analysis of volatile organic compounds by sorbent tube/thermal desorption/capillary gas chromatography 2．3参考民用建筑工程室内环境污染控制规范GB 50325-2001附录E：室内空气中总挥发性有机化合物(TVOC)的测定

非甲烷总烃（NMHC）

2．4空气和废气监测分析方法(四)中《总烃和非甲烷总烃测定方法一》《总烃和非甲烷总烃测定方法二》《气相色谱法测定非甲烷烃》

2.5固定污染源排气中非甲烷总烃的测定气相色谱法HJ/T38-1999

两者分析方法中各有侧重，VOC常用的方法是吸附剂吸附，因为吸附剂的选择性，所以没有一种吸附剂是适用于所有VOC，而GB 50325-2001附录E选择的tenax，有较广的吸附范围和较强的吸附能力。VOC另一种方法是直接用罐采样，在实验室里用通过冷阱冷凝-快速加热解析，进样，这种方法理论上可达到无损采样，对仪器设备要求较高。非甲烷总烃一般采用直接进样，通过做出总烃再减甲烷得出结果，不过在空气和废气监测分析方法(四)中第三种方法《气相色谱法测定非甲烷烃》也是通过吸附剂吸附-解析，再通过折算得非甲烷总烃。可见由于实验的操作不同，会决定所测量的VOC和NMHC的范围。

节选：

Introduction

Hydrocarbon emissions can be reported in a variety of styles depending on the en d use of the emission estimates and the measurement technique used in the under lying data. Not all emissions are measured for all engines, so a conversion from th e most common measurement type to others is needed to supply an estimate in te rms required by the user.

Most hydrocarbon emissions data from mobile sources is measured as total hydroc arbon (THC). THC is the measured hydrocarbon emissions using a Flame Ionizatio n Detector (FID) calibrated with propane. The FID is assumed to respond to all hy drocarbons identically as it responds to propane in determining the concentration of carbon atoms in a gas sample. Most hydrocarbons respond nearly identically as p ropane with notable exceptions being oxygenated hydrocarbons such as alcohols a nd aldehydes commonly found in engine exhaust.

Because alcohols and especially aldehydes are chemically reactive and therefore oz one-forming hydrocarbons, the California Air Resources Board defined a measurem ent that adds the THC and the oxygenated components into a new measurement c alled total organic gas (TOG).

[1] The oxygenated components are measured by collecting aldehydes on dinitro- p henylhydrazine impregnated filter traps and alcohols in chilled water impingers. The aldehydes and alcohols are extracted and measured using chromatography to dete rmine emission rates. Each mole of aldehydes and alcohols is added by weight as formaldehyde and methanol.

Methane is an organic gas that is orders of magnitude less reactive than other hyd rocarbons, so it is often excluded from emission estimations. The methane is meas ured by chromatographically separating the methane from the THC and analyzing t he concentrations using a FID calibrated specifically for methane. The methane emi ssions are subtracted from the THC and TOG emission estimations to produce a n onmethane hydrocarbon (NMHC) and a nonmethane organic gas (NMOG) emission estimate. Some newer instruments can measure the NMHC directly however leadi ng to lower uncertainty.

Some hydrocarbons are less ozone-forming than other hydrocarbons, so EPA has officially excluded them from the definition of regulated hydrocarbons called volatile organic compounds (VOC). This definition excludes methane, ethane, acetone, and compounds not commonly found in large quantities in engine exhaust like chlorohyd rocarbons from consideration as VOC. For this work, the definition of VOC is the r esult of subtracting methane and ethane from the TOG emission estimates. Althoug h acetone is not subtracted, it is present in smaller quantities compared to methan e and ethane, and will have a negligible effect on the results.