Specific Emission Mode Input Data in LOD 2#

For specific emission modes under LOD 2, emissions can be explicitly provided at a cell level. The LOD 2 emissions data are stored in a separate netCDF file in die model INPUT directory, and are read automatically. These input files are prefixed with the model name, followed by the keyword emis, then by the specific emission mode. For instance, the LOD 2 input for traffic emissions will be called [model]_emis_traffic, while that for the all-purpose generic mode will be called [model]_emis_generic, etc..

Please note that all emissions are to be expressed in SI units, i.e. kg, mol, m, and s. Further, unless otherwise indicated, reactive gas phase emission species, such as NO₂ or O₃ are to be provided in moles. On the other hand, tracer or inert species, such as PM₁₀ or pollen (in the pollen module), are to be specified in kilograms.

Temporal Emission Profiles#

Temporal profiles of emission are stored using the following format:

YYYY-MM-DD HH:mm:ss +ZZ

where YYYY-MM-DD represents the date in full numeric format, HH:mm:ss represents the local time in 24-hour format, ZZ is the time zone. It is generally recommended that the profiles are specified in coordinated universal time (UTC) to maximize reusability.

The user can specify profile with arbitrary start and end times, as well as intervals, in chornological order. Emissions data defined at the time closest but not later than the current model time will be used as input. Should the model start (as defined in the origin_date_time option in the _p3d file) prior to the earliest defined emission data, the earliest emission data will be used.

netCDF File Format#

Although the netCDF 4 API can be used to create the LOD 2 emisisons input files, storage of the emission data follow the netCDF 3 convention to maintain compatibility with other netCDF files used in the model. In particular, only the time dimension can be used as the UNLIMITED dimension, and strings are to be stored as arrays of characters, as opposed to the STRING variable type. User-defined data structures are not used.

Dimensions#

The definition of the LOD 2 emissions variables are predicated on the following mandatory dimensions:

Dimension name	Value	Description
ntime	at least 1	Designated UNLIMITED dimension
field_length	64	Fixed length of all string variables
nspecies	at least 1	Number of emissions species
nvsrc	at least 1	Number of volumetric emission sources

Note that the field_length dimension must be set to 64. Other dimensions must be greater than zero.

Variables#

The mandatory variables for storage of emissions can then be defined using the above dimensions:

Variable name	netCDF data type	Dimension(s)	Description
timestamp	NC_CHAR	(ntime, field_length)	Individual time stamps for each set of emission data
species	NC_CHAR	(nspecies, field_length)	Names of individual chemical species
vsrc_i, vsrc_j, vsrc_k	NC_INT	nvsrc	Cell coordinates (i,j,k) of individual emission sources
vsrc_[species]	NC_FLOAT	(ntime, nvsrc)	Volumetric emission of chemical species at each source location

The volumetric emission sources of each species are stored in separate variables with the prefix vsrc_, followed by the species name specified in the species variable. They are defined for all source cell locations (i,j,k) defined in the varibles vsrc_i, vsrc_j, and vsrc_k. As such, species not emitting at a particular location on a given time stamp must be given a emission value zero. The species indicated in the variable species can be of any name, but in general they should appear in the active kinetic mechanism used in the chemistry model. Species names not appeared in said mechanism and corresponding emissions will be ignored. NOTE: All volumetric emission sources are expressed in terms of mol/(m³s) for gas-phase species and kg/(m³s) for particulate matter (PM).

Example#

The following is the header of an example netCDF emission input file under LOD 2:

dimensions:
        ntime = UNLIMITED ; // (1 currently)
        nvsrc = 3 ;
        nspecies = 6 ;
        field_length = 64 ;
variables:
        char timestamp(ntime, field_length) ;
                timestamp:description = "Time stamps" ;
        char species(nspecies, field_length) ;
                species:description = "Emission species" ;
        int vsrc_i(nvsrc) ;
                vsrc_i:description = "i grid indices for volume source location" ;
        int vsrc_j(nvsrc) ;
                vsrc_j:description = "j grid indices for volume source location" ;
        int vsrc_k(nvsrc) ;
                vsrc_k:description = "k grid indices for volume source location" ;
        float vsrc_O3(ntime, nvsrc) ;
                vsrc_O3:description = "volume source values for O3" ;
        float vsrc_NO(ntime, nvsrc) ;
                vsrc_NO:description = "volume source values for NO" ;
        float vsrc_NO2(ntime, nvsrc) ;
                vsrc_NO2:description = "volume source values for NO2" ;
        float vsrc_PM10(ntime, nvsrc) ;
                vsrc_PM10:description = "volume source values for PM10" ;
        float vsrc_PM25(ntime, nvsrc) ;
                vsrc_PM25:description = "volume source values for PM25" ;
        float vsrc_SO2(ntime, nvsrc) ;
                vsrc_SO2:description = "volume source values for SO2" ;

While not shown, it should be apparent to the user that the species defined in the netCDF files correspond to the volumetric source variables present.