Mishra 2014_Volatile Organic Compounds-Characteristics, distribution and...

                                                          N. Mishra et al. / Atmospheric Environment xxx (2014) 1e7                                                              5

Table 1
PCA Analysis of outdoor VOCs.

 Factor        Sources                        Major compounds                              Comments/references

 1             Petrol Vehicle Exhaust         2- methyl hexane, 3-methyl hexane,           (Liu et al., 2008a), (Han and Naeher, 2006) reported similar compounds
                                              methylcyclohexane, heptanes,                 from petrol vehicle exhaust.
                                              2- methyl butane, toluene
 2             Fuel evaporation               2- methyl pentane, 3- methyl                 (Geng et al., 2010) suggested that these alkanes are also emitted from
               (petrol and diesel)            pentane, hexane, pentane                     fuel evaporation (petrol, LPG/NG and diesel). (Morikawa et al., 1998)
                                                                                           reported pentane as a tracer of petrol evaporation.
 3             Industrial sources             xylenes(m,-p-,xylene),benzene                (Liu et al., 2008b), (Guo et al., 2004) reported similar results in their research.
                                              benzaldehyde
 4             Solvent usage                  o-xylene                                     (Guo et al., 2004) found that o- xylene is one of the constituents of paints and
                                                                                           have also been associated with solvent use.
 5             Photochemical process          Acetone                                      (Atkinson, 2000; Vlasenko et al., 2009) mentioned that acetone is released as a
                                                                                           secondary product and has a long residence time in atmosphere.




factors to be retained (i.e. only factors with an eigenvalue >1)                         from the application of PCA to the indoor data (Table S8). Again,
(Kaiser, 1958). Marker compounds for specific sources were deter-                         Kaiser's criteria were adopted to identify the appropriate number of
mined based on published chemical composition profiles (Vega-                             factors to be retained (with only factors having eigenvalues >1
Baudrit et al., 2007; Shinohara et al., 2009; Kim et al., 2010;                          retained) (Kaiser, 1958). Altogether seven factors, representing
Yrieix et al., 2010; Yuan et al., 2010) as well as some prior knowl-                     seven different source categories, were identified, namely: 1. Out-
edge regarding the sources of VOC species. The five components in                         door traffic emissions; 2. Off-gassing of building materials and
Table S6 of Supplementary Information represent the following                            stationaries; 3. Decorating materials and computers, printers; 4.
source categories: 1. Petrol vehicle exhaust; 2. Fuel evaporation                        Personal care products; 5. Art and craft activities; 6. air fresheners;
(petrol and diesel); 3. Industrial sources; 4. Solvent usage; and 5.                     and 7. Cleaning products. All of these factors explained 88% of total
Photochemical process. Altogether, 84% of data variability was                           data variance.
explained by these five factors.                                                              The characteristics of the seven source categories obtained from
   The characteristics of the five factors representing the five                           the indoor dataset are summarized in Table 2.
source categories for the data are summarized in Table 2.                                    The source contribution from each factor is mentioned in the
   The contribution from each of the outdoor sources are described                       following section while the detailed description of these indoor
in section 3.4 while the detailed descripton of each factors are                         sources is included in S9 of the Supplementary information.
included in S7 of supplementary information.                                                 The main purpose of the PCA was to reduce the number of inter-
                                                                                         related variables in the original data to fewer number of factors,
3.4.2. Indoor VOCs                                                                       which are orthogonal to each other. The first factor accounts for the
    PCA was applied to indoor VOC data in the same way as the                            highest variability in the data and subsequent factors account for
outdoor data. Twenty two out of the 60 measured VOCs were                                progressively less amount of data variance. As it is a qualitative
selected for the PCA analysis. Seven components were extracted                           analysis, it provides the variance and pattern in the data set but the


Table 2
PCA analysis of indoor VOCs.

 Factor         Sources                                                    Major compounds                                     Comments/References

 1              Outdoor Traffic Emissions                                   2- methyl butane, 2- methyl pentane,                The outdoor concentrations of these
                                                                           3- methyl pentane, hexane,                          compounds were much higher than
                                                                           3- methyl hexane, heptanes, toluene                 indoor and the I/O ratio for these
                                                                                                                               compounds varied from 0.1 to 0.5,
                                                                                                                               so they could have penetrated inside
                                                                                                                               from outdoor air.
 2              Off- gassing of building materials and stationaries        a- pinene, benzaldehyde, m-, p-,o-xylene,           (Weisel et al., 2005)
                                                                                                                               reported the emission of a- pinene from
                                                                                                                               plywood. DSEWPC, 2001 mentioned xylenes
                                                                                                                               as a major solvent in pens/inks and coatings
 3              Decorating materials and computers, printers               2-ethyl 1-hexanol, phenol,n-nonanal,                Edwards et al., 2001) reported a similar
                                                                           styrene                                             result in their study of VOCs in Finland.
                                                                                                                               (Kagi et al., 2007) reported that styrene
                                                                                                                               is produced indoor air from printers,
                                                                                                                               computers
 4              Personal care products                                     Acetone, siloxane                                   (Bernstein et al., 2008) reported that
                                                                                                                               siloxanes are widely used in personal
                                                                                                                               care products. Acetone is also used as
                                                                                                                               one of the ingredients in such products.
 5              Art and craft activities                                   Acetic acid                                         (Colak and Colakoglu, 2004) found that
                                                                                                                               wood based materials elevated the level
                                                                                                                               of acetic acid.
 6              Air fresheners                                             Decanal                                             (Pluschke, 2004; Fukuda et al., 2010)
                                                                                                                               reported decanal as one of the compounds
                                                                                                                               in air fresheners.
 7              Cleaning products                                          Limonene                                            (Nazaroff and Weschler, 2004) reported
                                                                                                                               limonene as an active ingredient in cleaning
                                                                                                                               products.



 Please cite this article in press as: Mishra, N., et al., Volatile Organic Compounds: Characteristics, distribution and sources in urban schools,
 Atmospheric Environment (2014), http://dx.doi.org/10.1016/j.atmosenv.2014.10.052